1. Introducing
Physical
Geography
Alan Strahler
Chapter 2
The Earth’s Global Energy Balance
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2. The Earth’s Global Energy
Balance
Chapter 2
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3. Chapter Outline
1. Electromagnetic Radiation
Ozone Layer
2. Insolation over the Globe
3. Composition of the Atmosphere
4. Sensible Heat & Latent Heat Transfer
5. The Global Energy System
CERES – Clouds &
Earth’s Radiant Energy
Systems
6. Net Radiation, Latitude, &
Energy Balance
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4. 1. Electromagnetic Radiation
RADIATION AND TEMPERATURE
SOLAR RADIATION
CHARACTERISTICS OF SOLAR ENERGY
LONGWAVE RADIATION FROM THE
EARTH
THE GLOBAL RADIATION BALANCE
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5. 1. Electromagnetic Radiation
All surfaces emit radiation.
•Hot objects - radiation in the form
of light
•Cooler objects - emit heat
radiation.
Earth emits exactly as much energy
as it absorbs from the sun - energy
balance
Electromagnetic Radiation collection of waves, wide range of
wavelengths, travel away from the
surface of an object.
Wavelength is the distance separating one
wave crest from the next wave crest
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6. 1. Electromagnetic Radiation
Gamma rays and X rays – short wavelength, high energies,
hazardous to health.
Ultraviolet - 10 nm to 0.4 μm. Can damage living tissues.
Visible light - 0.4 to 0.7 μm. from violet blue, green, yellow,
orange, to red.
Near-infrared - 0.7 to 1.2 μm. Similar to visible light. From the
Sun. Cannot be seen because eyes not sensitive to radiation
beyond 0.7 μm.
Shortwave infrared - 1.2 and 3.0 μm. From the sun
Middle-infrared - 3.0 μm to 6 μm. From Sun or hot sources on
Earth (forest fires, gas well flames)
Thermal infrared – 6 μm to 300 μm. Given off by bodies at
temperatures found at the Earth’s surface.
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7. 1. Electromagnetic Radiation
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8. RADIATION AND
TEMPERATURE
Hot objects radiate more energy that cool
Hotter object, shorter wavelength
Suburban scene at night.
Black and violet tones - lower temperatures
Yellow and red tones – higher temperatures.
Ground and sky - coldest, windows of the heated homes warmest.
1. Electromagnetic Radiation
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9. SOLAR RADIATION
Sun - ball of constantly churning gases
heated by continuous nuclear reactions
(hydrogen to helium at high temperatures
and pressures)
•Surface temperature 6000°C (11,000°F)
•Rays of solar radiation spread apart as they
move away from the Sun
•Rate of incoming energy, solar constant
about 1367 W/m2
•Intensity of received (or emitted) radiation
= power of the radiation and the surface
area being hit by (or giving off) energy
1. Electromagnetic Radiation
Intensity of solar
radiation is greatest in
the visible portion of
the spectrum.
Most of the solar
radiation in the visible
spectrum penetrates
the Earth’s atmosphere
to reach the surface.
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10. CHARACTERISTICS OF
SOLAR ENERGY
Sun emits shortwave
radiation (ultraviolet,
visible and shortwave
infrared)
Earth emits longwave
radiation (infrared) - much
is absorbed by the Earth’s
atmosphere before it
leaves (e.g. by carbon
dioxide)
Radiation intensity is shown on a
logarithmic scale.
1. Electromagnetic Radiation
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11. LONGWAVE RADIATION
FROM THE EARTH
Earth radiates less
energy that the sun
•Energy radiated by
Earth is Longwave
•Wavelengths are
absorbed by gases in
the atmosphere, such as
water vapor and carbon
dioxide
1. Electromagnetic Radiation
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12. THE GLOBAL RADIATION
BALANCE
Shortwave radiation from the Sun transmitted through space,
intercepted by the Earth.
Absorbed radiation is then emitted as Longwave radiation to
outer space.
1.
1. Electromagnetic Radiation
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13. THE GLOBAL RADIATION
BALANCE
Incoming solar radiation is either:
• reflected (scattered) back to space, or
• absorbed by the atmosphere or surface
1. Electromagnetic Radiation
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14. THE GLOBAL RADIATION
BALANCE
Absorption of
shortwave radiation by
the Earth and
atmosphere provides
energy that the Earth –
atmosphere system
radiates away in all
directions.
1. Electromagnetic Radiation
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15. 2. Insolation over the Globe
DAILY INSOLATION THROUGH THE
YEAR
ANNUAL INSOLATION BY LATITUDE
WORLD LATITUDE ZONES
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16. 2. Insolation over the Globe
Insolation – the flow rate of incoming solar
radiation. It is high when the Sun is high in the sky.
• Angle of the solar beam striking the
Earth varies with latitude
• Insolation is strongest near the
equator and weakest near the poles.
• The intensity of the solar beam
depends on the angle between the
beam and the surface.
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17. 2. Insolation over the Globe
• Most intense when the beam is vertical.
• Beam at an angle of 45° covers a larger surface, less intense.
• At 30° beam covers greater surface, even weaker.
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18. DAILY INSOLATION
THROUGH THE YEAR
Daily insolation depends on:
1) Angle that the sun’s rays
strike
2) How long a place is exposed
to those rays
Midlatitude, mid summer –
days are long, sun’s position is
high – maximum heating
2. Insolation over the Globe
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19. DAILY INSOLATION
THROUGH THE YEAR
2. Insolation over the Globe
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20. DAILY INSOLATION
THROUGH THE YEAR
Equator - Sun’s path across the sky varies in position and
height above the horizon. Sun is always in the sky for 12
hours, but its noon angle varies through the year.
2. Insolation over the Globe
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21. DAILY INSOLATION
THROUGH THE YEAR
North Pole
Sun moves
in a circle in
the sky at an
elevation
that changes
with the
seasons.
2. Insolation over the Globe
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22. DAILY INSOLATION
THROUGH THE YEAR
Tropic of Capricorn the Sun is in the sky
longest and reaches
its highest elevations
at the December
solstice.
2. Insolation over the Globe
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23. ANNUAL INSOLATION BY
LATITUDE
Tilted Axis
• Annual insolation
varies smoothly from
equator to pole
• Insolation greater at
lower latitudes
• High latitudes receive
flow of solar Energy
• Insolation at poles 40
percent of equator.
2. Insolation over the Globe
Axis Perpendicular
• No seasons
• Annual insolation high
at the Equator, Sun
directly overhead at
noon every day
throughout year
• Annual insolation zero
at the poles,
• Sun’s below horizon.
Tilt redistributes
significant portion of
insolation from equator
to poles.
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24. WORLD LATITUDE ZONES
Globe divided into
broad latitude zones
based on the seasonal
patterns of daily
insolation observed
globally
2. Insolation over the Globe
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25. 3. Composition of the Atmosphere
Constant gases in
the Troposphere
Nitrogen 78%
(converted by bacteria
into a useful form in
soils)
Oxygen 21%
(produced by green
plants in
photosynthesis and
used in respiration)
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26. 4. Sensible Heat & Latent Heat
Transfer
Sensible heat – the quantity of heat held by an
object that can be sensed by touching or feeling
Latent heat - heat that is used and stored when a
substance changes state from a solid to liquid (or
directly to a gas) or liquid to gas (e.g. evaporation of
water)
Latent heat transfer – the transfer of heat from an
evaporating surface to the atmosphere
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27. 4. Sensible Heat & Latent Heat
Transfer
Sensible heat transfer refers to the flow
of heat between the Earth’s surface and
the atmosphere by conduction or
convection.
Latent heat transfer refers to the flow of
heat carried by changes of state of
water.
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28. 5. The Global Energy System
SOLAR ENERGY LOSSES IN THE
ATMOSPHERE
ALBEDO
COUNTERRADIATION AND THE
GREENHOUSE EFFECT
GLOBAL ENERGY BUDGETS OF THE
ATMOSPHERE AND SURFACE
CLIMATE AND GLOBAL CHANGE
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29. SOLAR ENERGY LOSSES IN THE
ATMOSPHERE
Clear Sky
80% of insolation reaches Earth’s surface
20% of insolation reflected back to space (3%
by scatter, 17% by molecules and dust)
Cloudy Sky
30 to 60% reflected by clouds
5 to 20% absorbed in Clouds
45 to 10% reaches Earth’s
surface
5. The Global Energy System
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30. ALBEDO
Albedo - percentage of solar radiation reflected
Snow and Ice – 0.45-0.85 (also expressed as
45 to 85%)
Black Pavement – 0.03
Water - 0.02
Fields, forests, bare ground - 0.03 to 0.25.
Earth and atmosphere system - 0.29 and 0.34.
Planet sends back to space slightly less than
one-third
5. The Global Energy System
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31. ALBEDO
Fresh snow has a high albedo,
reflecting most of the sunlight
it receives. Only a small portion
is absorbed
5. The Global Energy System
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32. ALBEDO
Asphalt paving
reflects little light, so
it appears dark or
black and has a low
albedo. It absorbs
nearly all of the solar
radiation it receives.
5. The Global Energy System
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33. ALBEDO
Water absorbs
solar radiation
and has a low
albedo unless the
radiation strikes
the water surface
at a low angle. In
that case, Sun
glint raises the
albedo.
5. The Global Energy System
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34. COUNTERRADIATION AND THE
GREENHOUSE EFFECT
Shortwave radiation passes
through atmosphere, absorbed
and warms surface.
5. The Global Energy System
Surface emits
longwave radiation
which goes
(A) directly to
space, or,
(B) absorbed by
atmosphere
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35. COUNTERRADIATION AND THE
GREENHOUSE EFFECT
Atmosphere radiates
longwave energy
back to the surface
and also to space as
counterradiation
(C & D)
Counterradiation
produces the
greenhouse effect.
5. The Global Energy System
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36. COUNTERRADIATION AND THE
GREENHOUSE EFFECT
Water vapor and carbon dioxide act
like glass allowing shortwave radiation
through but absorbing and radiating
longwave radiation.
5. The Global Energy System
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37. GLOBAL ENERGY BUDGETS OF THE
ATMOSPHERE AND SURFACE
5. The Global Energy System
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38. 6. Net Radiation, Latitude, &
Energy Balance
Net radiation difference between
incoming and
outgoing radiation
At high latitudes
there is an energy
deficit
Poleward - heat
transfer moves
surplus energy from
low to high latitudes
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39. Ozone Layer
Ozone Layer – Shield to Life
Ozone – form of oxygen with 3 oxygen
atoms (O3)
• Shelters Earth's surface from ultraviolet radiation
• Attacked by synthetic chemical components –
Chlorine, fluorine and carbons –
Chlorofluorocarbons (CFC’s)
• 1980’s hole in ozone discovered over Antarctica
• Ozone layer thins during the spring in the Southern
Hemisphere (September, October)
• 1987 – 23 nations signed treaty to cut CFC’s
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40. Ozone Layer
Ozone Layer – Shield to Life
The Antarctic ozone hole of 2006 was the largest on record 29.5 million square miles.
•Low values of ozone –purple, ranging through blue, green,
and yellow.
•Ozone concentration is measured in Dobson units
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41. CERES – Clouds &
Earth’s Radiant Energy
Systems
CERES – Clouds & Earth’s Radiant
Energy Systems
NASA study of the Earth’s radiation budget from
space for 20 years
•NASA Experiment—Clouds and the Earth’s
Radiant Energy (CERES)
•New generation of instruments in space that scan
the Earth and measure the amount of shortwave
and longwave radiation leaving the Earth at the
top of the atmosphere.
•Continuous monitoring of the Earth’s radiant
energy flows
•Small, long-term human or natural changes can
be detected
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42. CERES – Clouds &
Earth’s Radiant Energy
Systems
CERES – Clouds & Earth’s Radiant
Energy Systems
Average Shortwave Flux - 0 to
210 W/m2, March 2000
•Equator - thick clouds
reflect solar radiation back to
space.
•Midlatitudes - cloudiness
shows up as light tones.
•Tropical deserts - bright.
•Snow and ice is reflective,
amount of radiation at poles
low – so do not appear
bright.
•Oceans - absorb solar
radiation so low shortwave
fluxes.
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43. CERES – Clouds &
Earth’s Radiant Energy
Systems
CERES – Clouds & Earth’s Radiant
Energy Systems
Average Longwave Flux 100 to 320 W/m2, March
2000
•Equator – low values due
to blanketing of thick
clouds trapping longwave
radiation
•Tropical oceans - clear sky
emits high longwave flux
•Poles - surface and
atmospheric temperatures
drop, longwave energy
emission Low
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44. Chapter Review
1. Water in the Environment
2. Humidity
3. The Adiabatic Process
4. Clouds
Acid
Deposition
5. Precipitation
6. Types of Precipitation
7. Thunderstorms
8. Tornadoes
9. Air Quality
Observing
Clouds from
GOES
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