Download An introduction to the atmosphere

An introduction to the
atmosphere
Dr. Aldo Compagnoni
Postdoc research associate
Rice University (Houston, Texas, USA)
Layers of the atmosphere
High atmosphere
(heterosphere)
Low atmosphere
(homosphere)
Chemical composition of the lower
atmosphere
Atmosphere layers
The Earth’s energy budget: the Solar Constant
Solar constant: 1,366 W/m 2
Solar heating is uneven
•Different amounts fall on different parts of the earth
•Depends on the angle of the sun
The earth’s energy budget
The surface energy budget
The atmosphere energy budget
The earth’s energy budget
The greenhouse effect
The greenhouse gases
Climate change
Observed changes
IPCC 2007
Greenhouse gases are increasing
Global circulation models say: it is humans
Consensus?
Projections
IPCC 2007
The troposphere
Air temperature
1. Inclination of incoming radiation.
2. Altitude.
3. Presence of large water bodies.
4. Aspect.
5. Type of surface.
6. Clouds and dust.
7. Urbanization.
Atmospheric pressure
• The force exerted on a unit of
surface by the column of air
above it.
• Unit of measure: the millibar
(mb).
• Average atmospheric pressure:
1013.2 (mb).
• Measured with barometer
Isobaric maps
Winds and high/low pressure systems
General circulation of the atmosphere
Puzzle: Why are so many deserts found near 30° latitude?
Solar heating is uneven
•Different amounts fall on different parts of the
earth
•Depends on the angle of the sun
Uneven heating leads to uneven air pressure
Cold air sinks,
creating HIGH
pressure
Hot air rises,
creating LOW
pressure
Simplified circulation
But the earth is spinning too...
More on Coriolis forces...
Landmasses play a role as well
Warm air holds more moisture than cold air
Evaporation (add
energy)
Liquid
Gas
Condensation (release
energy)
Saturation vapor pressure
•“The saturation vapor pressure is the static pressure of a vapor when
the vapor phase of some material is in equilibrium with the liquid
phase of that same material.”
(Wickipedia)
•rate of condensation = rate of evaporation
•often occurs right at the surface of liquid water (or of a water droplet)
Hadley cell moves air
away from tropics up
here
Very cold up
here, moisture
has been
“squeezed out”
Cold air
sinks
Little moisture
left to begin
with
Upper
atmosphere
(COLD)
Sinking air
warms &
evaporation
increases
More cooling &
condensation
leads to rain
Air cools and
condensation
increases
cloud
Sea level (WARM)
Low
pressure
area
Hot air
rises
Tropics
Hadley cell
circulation
Warm air has
“sucked” all the
water out of the
clouds
High
pressure
area
Subtropics (30º)
The Big Picture
Subpolar low:
Cool and wet
Subtropical high:
Sunny and dry
Equatorial low:
Warm, cloudy, rainy
Polar
cell
Ferrel
cell
Hadley
cell
Elevation also influences climate
Orographic effects and rain
shadows
Latitude
Subpolar low 60°N
Westerlies
Subtropical high 30°N
In the winter, the westerly flow dominates all
of western and central North America
Westerly flow
Pacific winter storm
In the summer, SW and SE flow become
important
Westerly flow
SW
SE
Summer
thunderstorm
s in the
Great Plains
cm
Very cold and dry
H
Cold & wet
L
L
Cold
& wet
H
H
Warm & wet
Warm
& wet
continental polar
temperate
shrublands
maritime
polar forests
temperate
grasslands
forests
forests
subtropical
shrublands
maritime
subtropical
subtropical
grasslands
maritime
subtropical
maritime
polar
Climate diagrams
USA
°C 37.87°N / 122.25°W / 105m
BERKELEY
[102-104] +13.7°C 613mm
Years of data
Mean annual
temperature
50
Elevation
400
300
Annual
precipitation
200
100
90
40
80
70
30
60
50
20
40
10
20
10
0
-10
0
J F M A M J J A S O N D mm
Precipitation
Mean temperature
30
USA
°C 43.58°N / 118.95°W / 1265m
BURNS,OR.
[44-44] +7.8°C 277mm
50
400
300
USA
°C 40.65°N / 73.78°W / 4m
NEW YORK/JOHN F. KENN
[10-10] +12.3°C 1087mm
200
100
90
40
50
80
40
80
70
50
30
40
60
50
30
10
20
20
40
30
10
0
10
0
mm
20
10
0
-10
0
J F M A M J J A S O N D mm
-10
USA
°C 37.87°N / 122.25°W / 105m
BERKELEY
[102-104] +13.7°C 613mm
50
400
300
200
100
90
40
80
USA
°C 32.12°N / 110.93°W / 802m
TUCSON/INT., AZ.
[47-123] +20.2°C 288mm
50
60
40
40
30
20
20
-10
0
J F M A M J J A S O N D mm
100
50
80
60
40
10
20
-10
0
J F M A M J J A S O N D mm
300
200
100
80
70
30
60
50
20
40
30
10
20
10
10
0
400
90
40
30
10
0
200
USA
°C 39.20°N / 96.58°W / 325m
MANHATTAN
[130-132] +12.3°C 819mm
50
30
10
300
70
50
20
400
90
70
30
200
90
60
20
300
100
70
30
400
0
-10
0
mm
Periodic winds: monsoons
Sea breeze
Mountain breeze
Humidity
1. Absolute humidity
2. Relative humidity
3. Hygrometer
4. Dew point
Absolute versus relative humidity
Evaporation (add
energy)
Liquid
Gas
Condensation (release
energy)
Condensation and inverse sublimation
Condensation
Dew
Fog and clouds
Inverse sublimation
Hoar
Cloud types
Latent heat
Cloud formation: adiabatic cooling
Adiabatic cooling is cooling without heat transfer
Convective cooling
Convective cooling
Synoptic cooling
Cold front
Warm front
Orographic cooling
How does rain form?
Inverse sublimation
Coalescence
Hail formation
Precipitation regimes
1. Equatorial: high precipitation,
uniformly throughout year
2. Tropical: maximum
precipitation at summer
solstice
3. Temperate: precipitation is not
uniform in time and space
4. Polar: low precipitation
Weather in the tropics: cyclones
Cyclones move from East to West
The “sides” of a cyclone
Mediterranean tropical cyclones