Global average energy balance
GEO 101, Feb. 11, 2014
Any questions about
Ozone depletion?
Surplus
Greenhouse warming?
Deficit
Tropics
Temperature and pressure
Mid-High latitudes
San Francisco
St. Louis
Washington DC
How can Earth move energy from surplus to
deficit areas? (Methods of heat transfer)
2. Conduction
Only important at Earth/air interface
1. Radiation
All bodies above -460°F (-273°C) (0° Kelvin) radiate
energy.
Lower body temperature, longer wavelength.
Thermal infrared wavelength energy radiated by Earth
heats troposphere.
3. CONVECTION
Vertical currents
4. ADVECTION
Horizontal currents
1
Temperature & phase change
energy requirements for water
100 cal/g
20 cal/g
Temperature (sensible heat / energy)
Temperature depends on …
Depends On Three Things…
2. Reflectivity (albedo) of surface
1. Insolation
Intensity
x
Duration
angle of sun’s rays
latitude
atmospheric
transparency
season
altitude
Temperature depends on …
High albedo:
energy reflected,
surface cool
Low albedo,
energy
absorbed,
surface hot
Most land has low albedo. It absorbs radiation and heats up
3. Whether surface is land or water (continentality)
2
Relative rates of heat flow into soil and water
Temperature varies over time
5°C
10°C
20°C
40°C
Freezing
Summer Solstice
Soil
Winter Solstice
1990 Daily temperature ranges
Minneapolis-St.Paul
Water is transparent, mixes, reflective, evaporates
Water heats up (and cools down) slower than land 
CONTINENTALITY
Temperature varies
vertically. In the
troposphere, it
usually gets colder
as you go up.
This normal change
in temperature is
called the “normal”
or “environmental”
lapse (change) rate.
The normal lapse rate
would be like having
thermometers tied to a
tall tower that reached
to the top of the
troposphere and
taking a temperature
reading at each
thermometer at the
same time.
Troposphere
Temperature inversion: it gets warmer as you go up.
An inversion traps pollutants near the ground level
Altitude in meters
Surface inversion
(starts at surface)
Degrees Celsius
3
Temperature varies horizontally
Based on insolation and continentality
Altitude in meters
Inversion aloft
starts above surface
Degrees Celsius
Temperature varies horizontally
Based on insolation and continentality
Winter
40º
Horizontal variation in temperature
Average sea level temperature °F in July
Summer
0º
Summer
Atmospheric circulation redistributes heat and moisture
(latent heat) across Earth’s surface.
Atmosphere accounts for 87% of heat redistribution.
Ocean circulation moves the remaining 13%.
Atmosphere moves because
temperature differences cause
differences in atmospheric pressure
What is atmospheric pressure?
Can be thought of as weight of
column of air above you
Winter
Atmospheric pressure measured with a barometer
Atmospheric pressure at standard sea level ≈
29.92 inches of Hg
14.7 psi
1013 mb
1 bar = 29.53 inches of Hg at 32°F at 45°N
1000 mb (millibars) = 1 bar
4
500
Atmospheric Pressure varies with:
Atmospheric pressure decreases
with increasing altitude
312 mi
1. Altitude
400
Altitude (km)
Air molecules
300
200
Air density
100
62 mi
Air
pressure
90% in first
10 mi
Cool temperature,
molecules close
together, so more
fit, column is
heavier, pressure
is higher.
Atmospheric Pressure varies with:
2. Temperature
Temperature down, pressure up
10 mi
Warm temperature,
molecules far
apart, so fewer fit,
column is lighter,
pressure is lower.
Temperature up, pressure down
Relative
temperature
of
Season Insolation
Land
Water
Relative
pressure
of
Land
Water
Atmospheric Pressure varies with:
3. Moisture content of air
Moisture up, pressure down
Moisture down, pressure up
Average water molecule weighs less
than average air molecules
Summer
Atomic weight of molecules
N2 = 28 = 78% of air
Winter
O2 = 32 = 21% of air
H2O = 18
5
PRESSURE GRADIENT FORCE determines speed of wind
Differences in atmospheric pressure cause wind.
WIND: horizontal movement of air (advection)
Low pressure
Air molecules flow from high pressure to low pressure
Low pressure
960
960
970
970
980
980
990
PRESSURE GRADIENT FORCE determines speed of wind
1000
Difference in surface pressure over given distance
1010
Similar to slope (rise / run)
1020
990
1000
High pressure
Steep gradient =
faster winds
1010
1020
High pressure
PRESSURE GRADIENT FORCE determines speed of wind
High pressure does not move toward low pressure…
Difference in surface pressure over given distance
Air molecules flow from high to low pressure areas
80
60
40
20
0
Winds named by direction they come FROM!
Windward: side the wind blows upon
For us, North wind is cold…comes from the north
Leeward: side the wind blows away from
South wind is warm…comes from the south
6
Local Winds set up by daily temperature variation
Land / sea breeze
Local Winds set up by daily temperature variation
Day
Land / sea breeze
Day
Night
Low
High
Warm
High
Cool
Low
Warm
Cool
Local Winds set up by daily temperature variation
Local Winds set up by daily temperature variation
Day
Mountain / valley breeze
Day
Mountain / valley breeze
Night
Low
Low
Warm
Valley
Breeze
Warm
High
High
Cool
Mountain
Breeze
High
Low
Warm
Cool
Wind is the mechanism by which Earth system…
Balances pressure
Cool
High
Divergence
aloft
Low
Convergence
aloft
Transports moisture onto land
Transports energy toward polar deficit areas
in atmosphere as latent heat
Rising
air
Descending
air
by driving ocean currents
Low
Converging
air
High
Diverging
air
7
Coriolis Force: an apparent force caused by earth’s rotation
that deflects freely moving objects from their path of motion.
To right of path of motion, in northern hemisphere
To left of path of motion, in southern hemisphere
Coriolis Force is strongest near the poles,
weakest near the equator.
The faster the object moves, the greater Coriolis Force
acts upon it.
Rotation
Because wind is a freely moving object,
the Coriolis Force affects it.
Surface air flow
Northern hemisphere
Low
960
970
Surface air flow is
deflected to the right
of its path of motion
and crosses the
isobars at about a
45° angle because
of the Coriolis Force
and friction with the
earth’s surface.
Rotation
North
Pole
980
990
1000
1010
1020
High
Surface air flow
Southern hemisphere
Low
960
970
Surface air flow is
deflected to the left
of its path of motion
and crosses the
isobars at about a
45° angle because
of the Coriolis Force
and friction with the
earth’s surface.
980
990
1000
1010
1020
High
Air flow aloft
Northern hemisphere
Low
960
Air flow aloft is
deflected to the right
of its path of motion
until it flows parallel
to the isobars
because of the
Coriolis Force and
no friction with the
earth’s surface.
970
980
990
1000
1010
1020
Geostrophic winds
High
8
Air flow aloft
Southern
hemisphere
Northern
Hemisphere High
Low
960
970
Air flow aloft is
deflected to the left
of its path of motion
until it flows parallel
to the isobars
because of the
Coriolis Force and
no friction with the
earth’s surface.
980
990
H
1000
In northern
hemisphere,
high pressure
cells rotate
clockwise.
Called anticyclones.
1010
1020
Geostrophic winds
High
Northern
Hemisphere Low
Southern
Hemisphere High
H
L
In southern
hemisphere,
high pressure
cells rotate
counterclockwise.
Called anticyclones.
L
In northern
hemisphere,
low pressure
cells rotate
counterclockwise.
Called
cyclones.
Southern
NECESSARY CONCEPTS
Hemisphere Low
1. Pressure is indirectly related to temperature.
In southern
hemisphere,
low pressure
cells rotate
clockwise.
Called
cyclones.
2. Air flows from areas of high pressure to areas of low
pressure.
3. The Coriolis Force deflects air flow to the right of its path
of motion in the Northern Hemisphere and to the left
of its path of motion in the Southern Hemisphere.
4. Surface low pressure has converging surface air flow,
rising air, and diverging air flow aloft.
5. Surface high pressure has diverging surface air flow,
descending air, and converging air flow aloft.
9