Energy: Warming the Earth & the Atmosphere This chapter discusses: 1. The role of solar energy (e.g.
Download ReportTranscript Energy: Warming the Earth & the Atmosphere This chapter discusses: 1. The role of solar energy (e.g.
Slide 1
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 2
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 3
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 4
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 5
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 6
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 7
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 8
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 9
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 10
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 11
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 12
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 13
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 14
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 15
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 16
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 17
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 18
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 19
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 20
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 21
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 22
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 23
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 24
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 25
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 26
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 27
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 28
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 29
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 30
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 31
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 32
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 33
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 34
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 35
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 36
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 37
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 38
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 39
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 40
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 41
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 42
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 43
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 44
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 45
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 46
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 47
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 48
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 49
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 2
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 3
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 4
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 5
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 6
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 7
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 8
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 9
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 10
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 11
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 12
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 13
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 14
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 15
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 16
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 17
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 18
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 19
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 20
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 21
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 22
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 23
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 24
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 25
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 26
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 27
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 28
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 29
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 30
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 31
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 32
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 33
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 34
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 35
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 36
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 37
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 38
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 39
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 40
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 41
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 42
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 43
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 44
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 45
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 46
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 47
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 48
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.
Slide 49
Energy: Warming the Earth & the Atmosphere
This chapter discusses:
1. The role of solar energy
(e.g. short wave radiation) in
generating temperature & heat
2. Earth's processes for heat
transfer in the atmosphere,
including long wave radiation,
to maintain an energy balance
What is Energy?
• Energy is the ability or capacity to do work
on some form of matter.
• Work is done by pushing, pulling, or lifting
of matter.
• Since the size of the atmosphere is
undefined, the size of the atmosphere is
handled on a case-to-case basis.
• Two types of energy
– Potential Energy (PE) = mass × gravity × height
– Kinetic Energy (KE) = ½ × mass × velocity2
PE = mass × gravity × height
• Defines as the total amount of energy stored in
any object determines how much work that object
is capable of doing.
• Can be thought of as an internal energy.
• Also called gravitational potential energy.
• Since this course only deals with the earth's
atmosphere and gravity changes in the troposphere
are very minimal, gravity is held as a constant.
• Example: a volume of air aloft has more PE than
the same size volume of air just above the surface.
Why?
KE = ½ × mass × velocity2
• Once an object is set in motion then it is said to acquire
“energy of motion” or KE
• KE of an object is equal to ½ of its mass times the velocity
squared
• So mass and velocity of an object plays an critical role in
determining the KE
• Does an identical volume of air and water have the same
KE?
• Commonly refers to as heat energy
• A 75 miles per hour (mph) wind (minimal hurricane-force)
is likely to knock someone over than a strong breeze of 20
mph due to the minimal hurricane-force wind having more
energy. Now let's take this example further, a 75 mph wind
at Boulder, CO versus a 75 mph over Miami, FL have
different KE values. Why?
Energy
• Energy comes in many forms and can
change form from one to another.
• Energy cannot be created or destroyed.
• Energy is conserved during a change in
form.
• First law of thermodynamics
Temperature
• When solar radiation collides with atmospheric gas molecules, the gas molecules move.
This produces:
a) temperature, defined as the moving molecules average speed
b) kinetic energy
• Total energy increases with greater molecule volumes.
• The figure shows that how the average speed of the molecules can be the same but the internal
energy can be different.
Heat
• Defines as the process of energy being
transferred from one object to another
because of the temperature difference
between them.
• After the transfer, the heat is return to a
state of internal energy
• Heat can be transferred by:
– conduction
– convection
– radiation
Temperature Scales
•Thermometers detect the
movement of molecules to register
temperature.
• Fahrenheit and Celsius scales are
calibrated to freezing and boiling
water at sea-level, but the Celsius
range is about 1.8 times more
compact.
•While the Kelvin scale does not go
below 0K.
•The image below show how these
scales compare with one another
with respect to specific points and
events.
Specific Heat
• Defines as how much heat is needed to raise the
temperature of a substance that weights one gram
by one degree Celsius.
– Heat capacity is the ratio of the amount of heat
absorbed by a substance to the corresponding
temperature change
• Example:
– One gram of water would take one calorie to raise its
temperature by 1°C
– One calorie = 4.186 Joules
– Calorie (Cal) is the amount of heat required to raise the
temperature of 1 g of water from 14.5°C to 15°C.
Therefore, a kilocalorie is 1000 calories and is the heat
required to raise 1 kg of water 1°C.
• Water has special properties such as :
•Heat slowly
•High capacity of storing heat
•Why is this important?
Latent Heat
• Defines as the heat energy requires to
change a substance from state to another.
• This heat source is sometimes referred to as
a hidden warmth.
• Latent heat is released from or absorbed
within the water molecules when phase
change occurs.
Latent & Sensible Heat
•Heat energy, which is a measure of molecular motion, moves
between water's vapor, liquid, and ice phases.
• As water moves toward vapor it absorbs latent heat to keep the
molecules in rapid motion and vice versa.
•
•
•
•
Evaporation has a cooling effect
Condensation is a warming effect
Latent heat can manifest itself as sensible heat
Sensible heat is the heat that we can feel and measure with a
thermometer
• Latent heat of (at room temperature):
– Condensation (heat is added into the environment)
• Vapor to liquid
• 2.5 × 106 J kg−1
– Evaporation (heat is needed from the environment)
• Liquid to vapor
• 2.5 × 106 J kg−1
– Fusion (heat is needed from the environment)
• Ice to liquid
• 3.35 × 105 J kg−1
– Sublimation (heat is needed from the environment)
• Ice to vapor
• 2.83 × 106 J kg−1
– Deposition (heat is added into the environment)
• Vapor to ice
• 2.85 × 106 J kg−1
Heat Energy for Storms
•Latent heat released from the billions of vapor droplets during condensation and cloud
formation fuels storm energy needs, warms the air, and encourages taller cloud growth.
•An average thunderstorm contains several thousand metric tons of water.
•Condensing 1 kg of water releases ~ 2.5 x 106 J of latent heat energy .
•An average thunderstorm containing around 1500 tons of water will release 3.45
billion Joules of energy.
Heat is transferred by:
• Conduction - transfer of heat from molecule to
molecule with in a substance
• Convection - transfer of heat by the mass
movement of a fluid (in the vertical)
– Advection - transfer of heat or some atmospheric
properties from one area to another area (in the
horizontal).
• Radiation - transfer of energy from one object to
another without spaces in between heated
Conduction - Heat Transfer
•Conduction of heat energy occurs
as warmer molecules transmit
vibration, and hence heat, to the
adjacent cooler molecules.
• Warm ground surfaces heat
overlying air by conduction.
•Air is a extremely poor conductor
of heat.
•Heat transferred by conduction
always flows from warmer to
colder regions.
•Typically, the greater the
temperature difference, the faster
the heat transfer.
Heat Conductivity
Poor
Good
Convection - Heat Transfer
•Convection is heat energy moving as a fluid from hotter to cooler areas.
•Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence
cools. This is called convective circulation or a thermal cell.
•Any rising air “bubble” will expand and cool, and any sinking air “bubble” will compress and
warm.
•As the air parcel rises to a a lower pressure region, in order to equalize the pressure on the
inside, the parcel molecules inside push the parcel wall outward and expanding it.
How does radiation transfer energy from one
object to another without spaces in between
heated?
• Radiant energy or radiation travels in the
form of waves.
• Energy is released when they are absorbed
by an object.
• These waves are called electromagnetic
(EM) waves because it has magnetic and
electrical properties.
• In space, void of air molecules, EM waves
travel at 3 x 105 km s-1 or 186,000 miles per
second.
Radiation - Heat Transfer
•Waves can come in different sizes.
•Wavelength (λ) is a measurement of these wave sizes.
• All objects above 0 K release radiation, and its heat energy value increases to the 4th power of
its temperature.
•Stefan-Boltzmann Law: E = σT4 where σ is the Stefan-Boltzmann Constant.
•σ
= 5.67 x 10-8 W m-2 K-4
3 important facts about radiation
• All things emit radiation
– size does not matter.
• The wavelengths of radiation that an object emits are
mainly dependent on the object’s temperature.
– Temperature is inversely proportional to the wavelength -- the
higher the temperature of an object, the shorter the wavelength.
• Objects that have high temperatures emit radiation at a
greater rate, stronger intensity, and wider range than
objects with lower temperatures.
– Sun’s surface temperature is greater than earth’s surface
temperature therefore the sun emits more radiation and at more
wavelengths than the earth’s surface.
Longwave & Shortwave Radiation
•The hot sun radiates at shorter wavelengths that carry more energy.
•The sun maximum radiative wavelength is about 0.5 μm. (visible light)
•The cooler earth only absorbs a small fraction of the sun’s radiation which is then reradiated at longer wavelengths, as predicted by Wein's law.
•The earth maximum radiative wavelength is about 10 μm. (infrared)
How does Wien’s law work?
• Start with:
max
Constant
T
• λmax is the maximum radiation emission (μm)
• T is the temperature of the object
• Constant = 2897 μm K
max
3000 K
6000 K
Sun
0 .5 m
max
3000 K
10 m
288 K
Earth
• Sun emits shortwave radiation (solar radiation)
• Earth emits longwave radiation (terrestrial radiation)
Electromagnetic Spectrum
•Solar radiation is largely found in the shorter wavelengths such as ultraviolet,
visible, and near infrared portions of the EM spectrum.
•Solar radiation also extends at low intensity into longwave regions such as far
infrared, microwaves, and radio waves.
•7% UV + 44% VIS + 37% near IR+ 11% far IR + 1% others = 100%
• Earth’s surface and the sun are considered
blackbody objects. ~ nearly 100%
absorption and emission.
• When the rate of absorption equals the rate
of emission by radiation transfer only, this
is called the radiative equilibrium state.
• So, the temperature at which this state
occurs is known as radiative equilibrium
temperature (RET) ~ the earth’s RET is
about 255 K.
What is a Blackbody?
Any object that is a perfect absorber (to all radiation that strikes it) and a perfect
emitter (where the maximum radiation possible is emitted at its given
temperature).
•Does not have to be black to be considered a blackbody.
•Wein’s law and Stefan-Boltzmann law works well with blackbody objects.
50 % absorption
50 % emission
Therefore, the object is a
blackbody because its
absorption/emission
efficiency is at 100%.
So if the earth ’ s radiative equilibrium
temperature is about 255 K (0°F) why is this
value much lower than the earth’s observed
temperature 288K (59°F)?
• The earth’s atmosphere absorbs and emits
infrared radiation.
• The atmosphere does not behave like the
earth’s surface (blackbody).
• The atmosphere is a “selective” absorber
and emitter of radiation.
Atmospheric Greenhouse Effect
•Earth's energy balance requires that absorbed solar radiation is emitted to
maintain a constant temperature.
•Without natural levels of greenhouse gases absorbing and emitting, this
surface temperature would be 33°C cooler than the observed temperature.
Atmospheric Absorption
•Solar radiation passes rather freely through
earth's atmosphere, but earth's re-emitted
longwave energy either fits through a narrow
window or is absorbed by greenhouse gases and
re-radiated toward earth.
•As these gases absorb infrared radiation from
the earth’s surface, they acquire kinetic energy
(energy of motion).
•The different gas molecules share this energy by
collision with adjacent air molecules, such as O2
and N2 (poor absorbers of IR). These collisions
increase the overall kinetic energy of the air
which results in increase in air temperature
Absorption of Nitrous Oxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Methane
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Oxygen and
Ozone
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Water Vapor
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Absorption of Carbon Dioxide
|------UV--------|--VIS---|----------------------------------IR-------------------------------------|
Total Absorption of the
Atmosphere
• Atmospheric greenhouse effect is associated with the
role of water vapor, CO2, and other greenhouse gases in
maintaining the earth’s averaged surface temperature
higher than the predicted value without an atmosphere.
• Atmospheric Window is the region where IR radiation
(8 – 11μm) is neither absorbed or emitted by water vapor
and CO2 and is freely to pass through the atmosphere.
• Clouds (good absorber of IR but poor absorber of visible
light) can enhance the atmospheric gashouse effect as
well by absorbing radiation between 8 – 11μm, thereby
closing the atmospheric window.
–
–
–
–
Calm, cloudy night = warmer temperature
Calm, clear night = cooler temperature
Cloudy day = cooler temperature
Sunny day = warmer temperature
Warming Earth's Atmosphere from Below
1.
Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface
does it generate sensible heat (heat that we can feel and measure) to warm the ground and generate
longwave energy.
2.
This heat and energy at the surface then warms the atmosphere from below.
3.
Since water vapor decreases with rapidly above the earth, most of the absorption occurs in a layer near
the surface. Therefore, the lower atmosphere is mainly heat from below.
Scattered Light
•Sunlight passing through earth's
atmosphere is deflected by gases,
aerosols, and dusts in all
directions. This distribution of
light is called scattering.
•Air molecules are smaller than
visible light wavelengths,
therefore they are better scatterers
of shorter (blue) wavelengths than
longer (red) wavelengths.
•At the horizon sunlight passes
through more scatterers, leaving
longer wavelengths and redder
colors revealed.
•The midday sun looks white due
to less scattering by the air
molecules.
• At noon, the sun usually appears a bright
white due to less scattering of the blue
lights.
• At sunrise and sunset, sunlight must pass
through a thicker portion of the
atmosphere.
• As the sunlight passes through more of
the atmosphere, much of the blue light is
scattered out of the beam, causing the sun
to appear more red.
• Cloud droplets scatter all wavelengths of
visible white light about equally.
•This type of scattering by millions of tiny
cloud droplets makes clouds appear white.
•Sunlight can be reflected
from objects.
•Albedo – is the percent of
radiation returning from a
given surface compared to
the amount of radiation
initially striking the surface.
(reflectivity of a surface)
•The earth on the average
reflects about 30% of the
sun’s incoming radiation
back into space.
•The colors of the objects
do not play a huge role in
controlling the albedo.
Incoming Solar Radiation
Solar Constant – 1367 W/m2
•Solar radiation is scattered and reflected by the atmosphere, clouds, and
earth's surface, creating an average albedo of 30 (30 units).
•Atmospheric gases and clouds absorb another 19 units, leaving 51 units
of shortwave absorbed by the earth's surface.
Earth-Atmosphere Energy Balance
Earth-Atmosphere Energy Balance (cont.)
•The earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units
from atmospheric gases and clouds.
•These 147 units gained by earth are due to shortwave (sun) and longwave (atmosphere)
greenhouse gas absorption and emittance.
• Earth's surface loses 117 units through emission of IR, therefore producing 30 units of surplus
from the earth’s surface.
•Meanwhile, the atmosphere generates 30 units of deficit at the surface through conduction,
convection and evaporation.
•This 117 units lost from IR emission added with the 30 units lost from other processes equal
147 units.
•Basically, annually the earth is gaining as much energy as it is losing on the surface and
atmosphere. The balance is created from heat transfer processes such as absorption, conduction,
convection, and latent heat release.
•If this balance is shifted where the earth is gaining more energy then this will lead to a warming
trend and vice versa with the cooling trend.
Average annual incoming solar radiation absorbed and
outgoing infrared radiation from the earth and the
atmosphere
Surplus heat is transported from the equator to the pole regions.
Solar Particles and the Aurora
• Solar wind is made up of
charged particles from the
Sun’s atmosphere.
• These charged particles are
formed as a results of high
temperature stripping
electrons away from gases
in a violent collisions.
• Aurora are formed as a
result of the solar wind
interacting with the earth’s
magnetic field.
Earth's Magnetic Field
•Earth's molten metal core in motion creates a magnetic field that covers
earth from the south to north pole.
•This magnetic field forms the magnetosphere which protects the earth
from some of the solar wind bombardments.
Solar Wind
•High energy plasma is
blown from the sun in a
dangerous solar wind,
and the magnetosphere
deflects this wind to
shield the earth.
•This interaction
deforms the
magnetosphere into
teardrop shape.
•Solar wind normally
travels at a velocity of
400 km s-1 but can travel
faster during high solar
activities.
Ions
•Solar winds entering the magnetosphere excite atmospheric gas
electrons.
•The electron jumps into a higher energy orbit when excited by a
charged particle.
•When the electron de-excites it emits visible radiation.
Aurora Belts
•The aurora is created by these solar
winds and de-exciting ions, and has
belts of expected occurrence at both
poles.
•Aurora Borealis (northern lights)
•Aurora Australis (southern lights)
•Solid red light indicates where the
aurora would be best seen on a clear
night.
•The number of aurora events decreases
as you go north and south of the main
belt.
•The NP flag depicts the geographic
north pole and MN flag denotes the
magnetic north pole.