Transcript Document

Meteorology
5.01 Heating and Cooling of the Atmosphere
References:
FTGU pages 123, 124, 136 and 137
5.01 Heating and Cooling
of the Atmosphere
• MTPs:
– Vertical Structure
– Composition
– ICAO Standard Atmosphere
– Temperature Scales
– Atmospheric Properties
– Atmospheric Density
– Temperature Differences
– Heating and Cooling
Vertical Structure
• Troposphere
– Weather happens here
– To 25,000 – 30,000
feet over poles
– To 55,000 – 65,000
feet over equator
– Temperature
decreases with height
• Stratosphere
– Troposphere to
170,000’
– Temperature increases
with height
Vertical Structure
• Mesosphere
– Stratosphere to 270,000’
– Temperature decreases
with height, to -85°C
• Thermosphere
– Tops at 1.1 million to 2.6
million feet (350-800
kilometres)
– Temperature increases with
height, up to 1,500°C
• Exosphere
– Mainly comprised of
hydrogen and helium
– Extends into space
Vertical Structure
Vertical Structure
• Label the layers of
the atmosphere!
• Choose from these:
– Stratosphere
– Thermosphere
– Exosphere
– Troposphere
– Mesosphere
Composition
• The atmosphere is made up of a mixture
of gases
– Nitrogen (78%)
– Oxygen (21%)
– Other (~1%) (Argon, CO2, Water Vapour etc.)
– Although water vapour is less than
1% of the atmosphere, it remains
the most important component
from the standpoint of weather,
based especially on its ability to
change state
Nitrogen
Oxygen
Other
ICAO Standard Atmosphere
• The International Civil Aviation
Organization (ICAO) Standard
Atmosphere:
– Sea Level for North America
– Based on summer and winter averages at
40°N latitude
• The Standard:
– MSL pressure of 29.92” Hg (1013.25 hpa)
– MSL temperature of 15°C
– Air is a “perfectly dry gas”
– Lapse rate of 1.98°C per 1000 feet
Temperature
• Sun heats earth, earth heats atmosphere
• Celsius (nearly worldwide):
– Freezing point of water: 0°C
– Boiling point of water: 100°C
Atmospheric Properties
• Mobility
– The ability for air to move
– Atmosphere like an “ocean of air”
– Wind like “streams of water”
– (Much more freedom of
movement with air than water)
• Compression
– Air is compressed as it descends into greater
pressure
– Occupies less space
Atmospheric Properties
• Expansion
– As air rises, it reaches areas of lower
pressure, causing it expand and cool
– This cooling can be enough to condense
water vapour in the air, forming cloud
– This is why clouds and precipitation are
common in areas of rising air
– From a meteorological standpoint, the
most important property of the air!
– www.youtube.com/watch?v=Li9eyds1Y_g
Atmospheric Properties
Density - mass per unit volume
• Cold air is dense:
– Molecules are move slowly and
are packed close together
– Heavier and tends to sink
• Warm is less dense:
– Molecules are moving rapidly
taking up more space (or less
molecules in the same space)
– Warm air is lighter and is pushed up by the cold air
Atmospheric Density
• Density Relationships:
–Density vs. Temperature:
• Indirectly proportional
–Density vs. Humidity:
• Indirectly proportional
–Density vs. Pressure:
• Directly proportional
Confirmation
• Questions
• 1. What is the most important property of the
atmosphere?
• 2. If the density of the air increases, what
happens to the pressure?
• 3. What gas makes up the majority of the
atmosphere?
– Nitrogen 78%
Temperature Differences
• Horizontal Temperature Differences
– Diurnal Variation
– Seasonal Variation – earth’s tilt
– Latitude- north pole versus equator
– Topography
• Land and water differences
– Clouds
• Clouds reflect large amounts of solar
radiation
• At night, clouds trap the heat radiated off
the earth
Atmosphere Heating
• Types of Atmospheric
Heating:
– Radiation (heating)
• Earth absorbs
sun’s
short wave
radiation
• The lower
atmosphere
is then heated by
the earth
LONG & SHORT WAVE’S
SHORT WAVE
INSOLATION
LONG WAVE
TERRESTRIAL
RADIATION
6
Atmospheric Heating
– Conduction
• If two substances are
in contact, heat will
flow from the warmer
to the colder
substance
• Air is a poor
conductor, so this
usually only occurs in
small layers
• Same as the heat
transferred when
roasting
marshmallows
Cold air
Solar radiation
Cool air
Air warmed by conduction
warm surface
Atmospheric Heating
– Convection
• Air heated
through
conduction
becomes
buoyant and
rises
• This air then
heats the air in
the upper
atmosphere
Convection
COLD AIR
mixing
occurs
COLD AIR
warm
air
rises
COLD AIR
heat is carried
vertically
by convection
WARM SURFACE
9
Atmospheric Heating
– Advection
(heating)
• Occurs when
cold air moves
over a warm
surface and its
lower layer is
heated by
conduction
Advection
COLD
advective warming
WARM SURFACE
WARM
Atmospheric Heating
– Turbulent Mixing
• Turbulent air
mixes a
warmer
surface layer of
air with an
unheated air
aloft, spreading
the heat
upward
TURBULENT MIXING
 WIND CAUSES
TURBULENCE
 MIXES LOW
LEVEL HEAT TO
UPPER LEVELS
Cool air
Turbulent
mixing
warm air
warm surface
11
Atmospheric Heating
–Compression
• As air
descends it
compresses
due to
increased
pressure and
therefore
heats up
Compression
Sinking Air is
compressed by
higher pressure
and its temperature
will increase
Atmospheric Cooling
– Advection cooling
• Lower levels only
• When air is cooled
by moving over a
colder surface
• Cooling occurs as a
result of conduction
between air and
surface
• Some mechanical
turbulence can aid
in spreading cooling
effect
Advection Cooling
Warm Air moving
Over a cooler surface
WARM
advective cooling
COLD
cool surface
Atmospheric Cooling
– Expansion cooling
• The most
important cooling
process of the air
• Air forced to rise
experiences
lower pressure
and is allowed to
expand
• This expansion
causes decrease
in temperature
Expansion Cooling
Lower pressure
AIR
EXPANDS
&
COOLS
WARM
COOL
Lower pressure
Confirmation
Questions
1. Name 2 types of atmospheric heating
2. Name 2 types of atmospheric cooling
3. Describe how the earth is heated and
cooled through radiation.
4. Which layer of the atmosphere contains all
weather?
Soaring