The Earth’s Energy Balance
Principles of Physical Geography
The Earth’s Energy Balance
Aims
To understand the Greenhouse effect
To understand the temperature profile in the atmosphere
To understand the energy balance of earth and its components
To understand the global patterns of sea level temperature
To understand the basic reason for air pressure
Objectives
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To distinguish between solar and terrestrial radiation
To explain how the lower atmosphere is heated
To define the Greenhouse effect and give a value for its magnitude
To discuss the role of clouds
To describe the general characteristics of the layers in the earth's atmosphere based
upon the vertical variation in air temperature.
To identify the causes responsible for this temperature profile.
To identify the cause for the vertical change in air pressure
To explain hear transport mechnism within the atmosphere
To explain the overall energy budget of Earth and its atmosphere
To explain the hemispheric energy budgets of Earth and its atmosphere
To identify the major periodicities in air temperature and their reasons
To define the daily mean, daily range, monthly mean, annual mean and annual range
of temperature and to compute them at a locale from a provided data set.
To recognize the influence of the major controls of temperature upon the world temperature distribution
To define an isotherm and explain their major global features throughout the year
The Earth’s Energy Balance
Outline
Introduction
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Sea level temperatures
Emission and absorption of terrestrial radiation
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Heating of the lower atmosphere
The Greenhouse effect
Clouds
The temperature profile and its causes
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Radiation absorption at different heights in the atmosphere
Heat transfer within the atmosphere
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Radiation
Conduction
Convection
Latent heat
Energy budget of Earth and its atmosphere
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Contributions of different energy transfer mechanisms
Energy recycling via long wave radiation between atmosphere and Earth’s surface
Temperature patterns
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Mean temperatures
Global and regional pattern
Differential heating of land and water
Cycles of surface temperature and their causes
Latitudinal energy budgets
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Impact of the global circulation
Energy transfers and the global circulation
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Oceanic heat transport
Heat transport by the atmosphere
The Earth’s Energy Balance
Aims
• Greenhouse effect
• Temperature profile in the atmosphere
• Energy balance of earth and its components
• Global patterns of sea level temperature
• Basic reason for air pressure
Outline
Introduction
Emission and absorption of terrestrial radiation
The temperature profile and its causes
Heat transfer within the atmosphere
Energy budget of Earth and its atmosphere
Temperature patterns
Latitudinal energy budgets
Energy transfers and the global circulation
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The Earth’s Energy Balance
Bullets
Introduction
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Sea level termperatures
About 15oC - much higher than expected from blackbody temperature
Bands according to insolation
Land/ocean contrast
ocean currents
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heating of the lower atmosphere mainly through backradiation of Earth's surface and
absorption of long wave
hardly any heating of the troposphere by short wave
short wave <-> long wave
the atmospheric window for longwave radiation
more CO2 might decrease long wave loss through the atmospheric window and thus
lead to a warmer atmosphere and consequently a warmer surface, too
delicate balance of absorption and emission maintains current climate; important to
understand it
during days more sun light reflected from clouds - cooler
during nights more long wave radiation radiated back to the surface (water!) - warmer
Emission and absorption of terrestrial radiation
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The temperature profile and its causes
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Long wave absorption near the ground leads to decreasing temperature with height
Short wave/UV absorption in the stratosphere leads to increasing temperature with
height
Heat transfer within the atmosphere
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conduction - transfer of heat by molecular activity, one molecule pushing the other
convection - transfer of heat by movement of warm air; in meteorology upward or
downward
transfer of heat by evaporation of water in one place and the condensation of the
water vapor in another
evaporation of water requires energy thus water vapor has a higher energy content
than liquid water (first law of thermodynamics!) This energy is released again, when
the water condensates
Energy budget of Earth and its atmosphere
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30% of solar radiation reflected
19% absorbed by atmosphere and 51% by Earth’s surface
long wave radiation emission and absorption heats lower atmosphere
heat recycling via long wave radiation between atmosphere and Earth’s surface most
important
latent heat transfer is very important
most of Earth’s surface is covered by water and ice, thus a lot of radiation is absorbed
by water and used for evaporation
condensation transfers all this energy to the atmosphere
conduction and convection
Temperature patterns
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Diurnal cycles of radiation and temperature, driven by Earth’s rotation
Daily maximum temperature normally lags radiation
Temperature increases as long as the input is larger than the output
The Earth’s Energy Balance
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Only after solar input is smaller then the long wave loss, temperature decreases
Diurnal amplitude depends on: sun-angle variation, winds, cloudiness
Seasonal cycle of radiation and temperature, driven by Earth revolution around the
sun and the Sun-Earth relationships, mainly the tilt of the axis
Minimum and maximum radiation at the Solstices
Latitudinal energy budgets
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Transport of heat by water and air warmed near the tropics towards the poles.
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Ocean currents.
Warm water releases heat to the atmosphere by conduction and evaporation
Transport of heat in warm air
Transport of water vapour and heat release when condensations occurs
Tansport of heat in warm air.
Energy transfers and the global circulation
Links
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http://cwx.prenhall.com/bookbind/pubbooks/aguado2/chapter3/deluxe.html
The Earth’s Energy Balance
Sea level
temperatures
25o
15o
5o
January
January
July
July
Source: Lutgens, F.K. and E.J. Tarbuck, 1998. The Atmosphere
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The Earth’s Energy Balance
Emission and Absorption of terrestrial radiation
Global picture
Heating of the lower atmosphere
Source: Lutgens, F.K. and E.J. Tarbuck, 1998. The Atmosphere
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The Earth’s Energy Balance
Radiation absorption in the atmosphere
Blackbody
curves
6000oK
255oK
solar,
short-wave
Absorption (%)
Ground
level
O2 , O 3
11 km
terrestrial,
long-wave
Atmospheric
window for
CO2, H2O, CH4, N2O longwave
radiation
The atmosphere is heated from below!
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The Earth’s Energy Balance
Composition of the Atmosphere near the Earth’s Surface
Source: Ahrens, D., 1994. Meteorology Today. West publishing, Minneapolis/ St.Paul
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The Earth’s Energy Balance
The role of clouds
Earth’s short wave reflectivity in January
Equator
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The Earth’s Energy Balance
Source: Lutgens, F.K. and E.J. Tarbuck, 1998. The Atmosphere
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The Earth’s Energy Balance
The greenhouse effect II
Use Stefan Boltzmann law: E=σT4
Now consider atmosphere and albedo:
space
atmosphere
Ω/4
σT14
surface
2 σT14= σTs4 - Fw
Fw
σT14
T1
σTs4
(1-α)*Ω/4 = σT14 + Fw
Fw = 20Wm-2
240= σT14 + 20 => 220= σT14
440= σTs4 - Fw
Ts T =(460/σ)1/4
s
Ts=(460Wm-2/(5.67 x 10-8Wm-2K-4))1/4=(460/5.67)1/4x100oK ≈ 3x100oK=300oK
Too warm! Other energy transfers have to be considered
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The Earth’s Energy Balance
Energy transfer within the atmosphere
• Radiation
Strongly linked to gases in the atmosphere (location and species)
• Conduction (heat transfer during contact)
• Convection (heat transfer by transport of matter - air, water)
• Latent Heat (heat transfer by evaporation/condensation)
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The Earth’s Energy Balance
Latent Heat
Source: Ahrens, D., 1994. Meteorology Today. West publishing, Minneapolis/ St.Paul
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The Earth’s Energy Balance
The energy budget of Earth and its atmosphere
Source: Lutgens, F.K.
and E.J. Tarbuck, 1998.
The Atmosphere
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The Earth’s Energy Balance
Temperature patterns
Patterns in space and cycles in time
Vertical temperature profile in the atmosphere
• important for precipiation and stability
Horizontal spatial patterns
• important for circulation
Cycles of temperature
• important for circulation
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The Earth’s Energy Balance
The temperature profile and its causes
Thermosphere ~80km up
Mesosphere ~50~80km
Stratosphere ~10~50km
Troposphere 0~10km
Source: Ahrens, D., 1994. Meteorology Today
West publishing, Minneapolis/ St.Paul
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The Earth’s Energy Balance
Pressure profile in the atmosphere
Stratosphere
Troposphere
Source: Ahrens, D., 1994.
Meteorology Today. West publishing,
Minneapolis/ St.Paul
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The Earth’s Energy Balance
The vertical temperature gradient of the atmosphere
Get together in groups of four (with people behind or in front of you)
Speculate: What are the causes for the vertical temperature gradient in
the atmosphere up to about 30 km?
Note: causes for some parts of the temperature gradient:
• the decrease with height in the troposphere
• the increase with height in the stratosphere
• the decrease with height in the mesosphere
on a sheet of paper and hand in. No names necessary
Hint: Consider the radiation types coming in and going out through and
from the atmosphere, the properties of the different gases and the energy sources.
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The Earth’s Energy Balance
Cycles of surface temperature and their causes
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The Earth’s Energy Balance
Earth’s
motion
around
the sun
Source: Guyot,
G., 1998. Physics of the Environment and
Climate. After:
Iqbal, 1983
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The Earth’s Energy Balance
Diurnal cycle
Surface
cooling
Surface cooling
Surface warming
Source: Lutgens, F.K. and E.J. Tarbuck, 1998. The Atmosphere
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The Earth’s Energy Balance
Seasonal cycle
Radiation per area under different angles
Summer
Winter
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Causes different
amount of incident
energy at different
times of the year on
same area.
Also:
In winter the path of
sun’s radiation
through atmosphere
longer
The Earth’s Energy Balance
Incoming solar radiation Summer/Winter
NH Summer
Same amount
of radiation
top of atmo.
Distributed
over different
ground areas
Different sun angle causes seasons
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NH Winter
The Earth’s Energy Balance
Seasonal cycle of North-South distribution of solar radiation
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The Earth’s Energy Balance
Summer/
Winter
Continents/
Oceans:
Heat capacity
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The Earth’s Energy Balance
Latitudinal energy budgets
Annual
Radiation budgets
at the top of the
atmosphere
December
June
Source: Lutgens, F.K. and E.J. Tarbuck, 1998. The Atmosphere
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The Earth’s Energy Balance
Heat transfers and the global circulation
Southward
Northward
Total
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Latent Heat
Ocean
Sensible Heat
The Earth’s Energy Balance
Summary
• Atmosphere mainly heated by absorption of terrestrial radiation
• Recycling long wave radiation in lower atmosphere (Greenhouse Effect)
• Greenhouse gases mainly CO2, H2O
• Absorption of solar and terrestrial radiation by different gases and the
direction of the radiation explains atmospheric temperature gradient
• Latent heat
• Long wave radiation and convection most important energy fluxes
leaving Earth’s surface
• Global patterns of sea level temperature
• Diurnal cycle at a location
• Seasonal cycle
• Poleward heat transport by atmosphere and ocean
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