Transcript ENERGY, HEAT AND TEMPERATURE
ENERGY, HEAT AND TEMPERATURE
1 4/30/2020 (c) Vicki Drake, SMC
ENERGY
The ability or capacity to perform work on some form of matter Matter is any substance that takes up space and has mass Earth’s atmosphere is considered ‘matter’ – all the gas molecules and particulates Energy may be considered as either
Kinetic
or
Potential
Source of Energy for Earth: Sun Lecture will describe how the Sun’s energy works on Earth’s atmosphere 4/30/2020 (c) Vicki Drake, SMC 2
Potential Energy
Stored Energy: Value of potential energy (PE) determined by work capability Total amount of stored energy due to position Potential energy examples: A battery Water behind a dam Any object lifted against pull of gravity 4/30/2020 (c) Vicki Drake, SMC 3
Kinetic Energy
Energy in motion Value of Kinetic Energy (KE) is determined by the speed and mass of object Examples of atmospheric KE Heat energy Solar energy Light energy Electrical energy 4/30/2020 (c) Vicki Drake, SMC
E k = ½ mv
energy,
m 2
where
E k
is kinetic is the mass of the object and
v 2
is the square of the velocity of the mass 4
Internal Energy
Internal Energy is the stored PE and KE of atoms and molecules in any kind of matter or substance In theory:
PE = KE
The energy associated with random, disordered motion of molecules 4/30/2020 (c) Vicki Drake, SMC 5
1
st
Law of Thermodynamics (Newton)
Conservation of Energy
: Energy cannot be created or destroyed. It can only change form (i.e., converted to another type of energy).
Energy is a constant in the universe Conversion of Energy examples: Heater/Furnace: Chemical → Heat Automobile Engine: Chemical → Mechanical Nuclear: Heat → Kinetic → Optical Battery: Chemical Sound or Mechanical or Optical or… 4/30/2020 (c) Vicki Drake, SMC 6
Temperature: Measuring Energy
Temperature is a measurement of the
average
kinetic energy of atoms/molecules in a substance Temperature is measured using a Thermometer A thermometer measures the temperature of a system in a quantitative way.
‘Mercury-in-glass’ type has a bulb filled with mercury that expands into a capillary when warmed.
Rate of expansion calibrated on glass scale 4/30/2020 (c) Vicki Drake, SMC 7
Thermometer Scales: Interpreting Energy
Fahrenheit
: developed by Gabriel Fahrenheit in the 1700s.
Boiling point of water: 212 0 Freezing point of water: 32 0
Celsius
measure : developed by Carolus Linnaeus using ‘centrigrade’ Boiling point of water: 100 0 Freezing point of water: 0 0
Kelvin:
An absolute temperature scale, based on Absolute Zero, developed by William Thompson and Lord Kelvin Boiling point of water: 373K Freezing point of water:273K Absolute Zero: 0 degrees K -273 0 C or -459 0 F 4/30/2020 (c) Vicki Drake, SMC 8
What is Heat Energy?
Heat represents energy in the process of being transferred from one object to another because of a temperature difference.
Heat energy transfers are ‘one-way’ in natural environment
Heat energy transfer is from warmer objects to colder objects
4/30/2020 (c) Vicki Drake, SMC 9
What is Heat Capacity?
The ratio of the amount of heat energy absorbed by a substance Heat capacity is measured by a temperature increase in the receiving object that corresponds to the amount of heat energy applied to that object
Rapid temperature increase means the substance has a low heat capacity
Slow temperature increase means the substance has a high heat capacity
4/30/2020 (c) Vicki Drake, SMC 10
What is
Specific Heat
Capacity?
The amount of heat required to raise the temperature of 1 gram (1 g) of any substance by 1 degree Celsius All objects have their own increase
specific heat
capacity – the rate at which they will absorb heat energy and register a temperature The specific heat capacity of
water
all other substances are measured is the baseline against which Water has a baseline
specific heat
capacity of 1.0, while soil has a
specific heat
capacity of 0.2 (as measured against water).
Water can absorb 5 times more heat energy than ‘soil’ before a temperature increase is registered.
Water has a high specific heat capacity
Water heats slowly and releases heat slowly
Soil has a low specific heat capacity
Soil absorbs heat energy quickly and releases heat energy quickly
4/30/2020 (c) Vicki Drake, SMC 11
Latent Heat – “Hidden Heat”
Latent heat is energy absorbed and/or released by a substance during a ‘change of phase’ or ‘change of state of being’.
Latent heat is measured according to
water’s
response to absorbing or releasing energy.
Water is the only substance that exists in all three ‘states of being’ at the same time at earth’s ambient temperature and air pressure.
Solid (ice Liquid (water) Gas (water vapor) 4/30/2020 (c) Vicki Drake, SMC 12
Latent Heat and Change of Phase: Absorption and Release of Energy
4/30/2020 (c) Vicki Drake, SMC 13
Latent Heat – “Hidden Heat”
’ When change of phase is from a solid to a liquid and then to a gas, heat energy is absorbed.
This heat is ‘latent’ heat and cannot easily be measured as the ice melts into liquid water and then evaporates into water vapor.
When the change of phase is from a gas to a liquid to a solid, heat energy is released into the surrounding atmosphere.
This heat is also ‘latent’ heat, but the resulting increase in temperature of the surroundings can be measured as the water vapors condenses into droplets and then into ice crystals.
4/30/2020 (c) Vicki Drake, SMC 14
Change of Phase: Water
Evaporation
– heat energy absorbed by a substance changing water from a liquid to a gas (vapor) phase Evaporation is a ‘cooling’ process for a surface as heat energy is absorbed by water droplets, converting to a vapor, from surrounding atmosphere – “Latent Heat” (not easily measured)
Condensation
changing from a gas to a liquid phase
–
heat energy released by a water Condensation is a ‘heating’ process for a surface as heat energy is released by water vapor, converting to liquid droplets, into surrounding atmosphere – “Latent Heat” (easily measured as “Sensible Heat”) 4/30/2020 (c) Vicki Drake, SMC 15
Latent Heat’s Role in Energy
Latent heat is an important source of energy in atmosphere Heated water vapor molecules released during evaporation are swept to higher latitudes and altitudes Condensation of vapor to liquid releases heat energy to upper atmosphere Main energy source for: Thunderstorms Hurricanes Other mid-latitude cyclonic storms 4/30/2020 (c) Vicki Drake, SMC 16
Heat Transportation Mechanisms in the Atmosphere
Three processes work together to transport heat energy throughout the atmosphere and around the globe.
Conduction Convection Radiation 4/30/2020 (c) Vicki Drake, SMC 17
Conduction
Molecule-to-molecule transfer of heat energy Heat flows from warm to cold The greater the temperature difference, the more rapid the heat exchange Effective only in lower atmosphere where molecules are ‘compressed’ at the surface 4/30/2020 (c) Vicki Drake, SMC 18
Convection
Transfer of heat by currents in a fluid (liquid or gas) Uneven heating of Earth’s surface sets up conditions of warm air rising and cooler air sinking:
Thermals
Important part of heat transfer by expansion, rising, cooling and sinking of air within the lower atmosphere 4/30/2020 (c) Vicki Drake, SMC 19
Radiation
Radiant energy traveling in waves that release energy when they are absorbed by an object Waves have both magnetic and electric properties: ElectroMagnetic Spectrum Energy travels at the speed of light (C): 300,000 km/sec 186,000 miles/sec EM Spectrum – total amount of solar energy from Sun 4/30/2020 (c) Vicki Drake, SMC 20
Characteristics of Radiant Waves
Crests and troughs Wavelength (
λ
) – Distance from one crest to another Measured in units of meters, centimeters, micrometers (10 -6 ) and nanometers (10 -9 ) Higher energy waves have short wavelengths (higher frequency) 4/30/2020 (c) Vicki Drake, SMC 21
Radiation – Temperature Connection
All objects in universe (above Absolute Zero of -273K) emit radiation The higher the temperature of the object, the greater the amount of radiation emitted Stephen Boltzmann’s law:
E~ σT 4
E
= Maximum rate of radiation emitted per square meter of an object
σ
T
= a constant (5.67 x 10 -8 W/m 2 K 4 ) = Temperature of the object (in Kelvin) 4/30/2020 (c) Vicki Drake, SMC 22
Radiation: Solar Energy vs Earth Energy
Solar energy = 6000 K (10,500 0 F) Earth energy = 288 K (59 0 F, 15 0 C)
λ
max
for the Sun: ~0.5
μ
m (micrometer) the wavelength for “Blue” in the Visible Light portion of EM
λ
max
for the Earth: 10
μ
m (micrometer) the wavelength for Far Infrared (heat energy) in the EM Spectrum 4/30/2020 (c) Vicki Drake, SMC 23
Earth Energy Balance
4/30/2020 (c) Vicki Drake, SMC 24
Daily Temperature Variations
Daily Temperature Lag
Continual warming of air at Earth’s surface after Sun as reached solar peak at Noon Graph depicts the time of maximum insolation at local noon, while the maximum air temperatures occur past local noon 4/30/2020 (c) Vicki Drake, SMC 25
Daytime Heating
Air closest to surface heats through
conduction convection
processes and
Conduction
is not effective – strong temperature differences found just above surface
Convection
vertically of warm rising air (
Thermals
) redistribute air Sun is most intense at local Solar Noon (“local meridian”) Post-meridian (p.m.):
insolation
solar radiation) continues to be greater than outgoing longwave heat energy from Earth (incoming shortwave Energy surplus develops for 2-4 hours after Solar Noon Lag time develops between solar maximum and maximum heating of Earth’s surface 4/30/2020 (c) Vicki Drake, SMC 26
Nighttime Cooling
Lowered Sun angle, initially, spreads energy over wider area, reducing heat available to surface Earth’s surface and lower atmosphere lose more heat energy than gained Ground and air cooling via
radiational cooling
from Earth’s surface over night Night progresses – Earth’s surface and air layer closest to surface are cooler than upper level air Coldest time of 24-hour day? Just before sunrise!
4/30/2020 (c) Vicki Drake, SMC 27
Seasonal Lag time – Northern Hemisphere
Over the year – the Earth’s temperature shows a temperature lag behind the Sun’s insolation 4/30/2020 (c) Vicki Drake, SMC 28
Temperature Data
Diurnal Range of Temperature Difference between daily maximum and daily minimum temperatures Largest diurnal range: Dry, arid regions Low specific heat of soils Smallest diurnal range: Wet, humid regions High specific heat of water 4/30/2020 (c) Vicki Drake, SMC 29
What does diurnal range tell us?
Regions that have a low diurnal range are usually located near a body of water Regions that have a high diurnal range are usually located away from water 4/30/2020 (c) Vicki Drake, SMC 30
Mean and Average Daily Temperature
Average: Add all hourly values/24 Mean: Add Highest hourly value and Lowest hourly value/2 Collecting the average of mean daily temperatures for a particular location on a particular day for a 30-year period is the ‘normal’ or ‘average’ temperature for that place on that day 4/30/2020 (c) Vicki Drake, SMC 31
Average Monthly Temperature
The average of the mean daily temperatures for a month Add all the mean daily temperatures, divide by the total number of days in the month (‘average’) Mean average monthly temperature: Add the highest mean daily temperature for the month to the lowest mean daily temperature for the month and divide by 2 4/30/2020 (c) Vicki Drake, SMC 32
Annual Range of Temperature
The difference between the average temperature of the warmest month and coldest month Largest range – areas dominated by land “Continental” climates Smallest range – areas dominated by water “Maritime” climates 4/30/2020 (c) Vicki Drake, SMC 33
Mean Annual Temperatures
The average temperature for any place for an entire year Add mean temperature for the warmest month to the mean temperature for the coldest month and divide by 2.
Add all the average temperatures for each month (12 months) and divide by 12.
4/30/2020 (c) Vicki Drake, SMC 34
Controls on Temperature
# 1 control: amount of incoming solar radiation (insolation) reaching the Earth Seasonal shift of insolation due to rotation, revolution and tilt of Earth’s axis Latitude: Temperatures near Equator are more consistent year-round Further away from Equator – more variability of temperatures and cooler overall 4/30/2020 (c) Vicki Drake, SMC 35
Latitude as a Temperature Control
4/30/2020 (c) Vicki Drake, SMC 36
Unequal Heating of Land and Water
The difference in the specific heat of soils and water sets up conditions of differential heating and cooling of the land and water Specific heat of water is greater than the specific heat of ‘land’ ‘Land’ heats and cools at a faster rate than large bodies of water 4/30/2020 (c) Vicki Drake, SMC 37
Ocean Currents
Ocean currents move cool polar waters to the tropics as well as moving warm tropical waters to the poles.
Two types of ocean currents: Warm ocean currents Cool ocean currents 4/30/2020 (c) Vicki Drake, SMC 38
Elevation
The lower atmosphere (
troposphere)
cools at a fairly consistent rate from lower to higher elevations Lapse rate: a change in temperature with a change in elevation Environmental lapse rate is the average cooling/heating rate for rising/sinking air ~6 0 C/`1000 meters ~3.3
0 F/1000 feet 4/30/2020 (c) Vicki Drake, SMC 39
Albedo of Earth’s surfaces
Albedo is the amount of energy reflected back to space by different types of surfaces Ice/Snow have the highest albedo – the highest reflectance, low absorbance Vegetation has a low albedo absorbance – low relfectance, high Water has a low albedo, high absorbance 4/30/2020 (c) Vicki Drake, SMC 40