The first and second laws of Thermodynamics

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Last Class
The first and second laws of Thermodynamics The
laws that cover how energy can be used and how It
flows through the earth system
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The 2nd Law of Thermodynamics No transformation
of energy can be 100 efficient
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Energy Flow
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Today - Global Energy Balance What
transformations occur as energy flows through
the earth system. Relationship between
distance from the source and amount of energy
available. What are the characteristics of the
earth that allow an environmental temperature
that supports life as we know it.
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The r2 Law How much energy one receives depends
on how far you are from the source
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Energy Flow
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Energy Balance - No Atmosphere
apR2 S
4pR2 sT4
pR2 S
Incoming SW Radiation Reflected SW Radiation
Outgoing Longwave


pR2 S
apR2 S
4pR2 sT4
R Earths radius S 1370 Wm-2 a 0.3 s
5.67 x10-8 Wm-2 T 255oK
S (1 - a) 4?Tp4
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Our sun is really hot and emits most of its
energy at shorter wavelengths. The earth is
relatively cool and emits energy at longer
wavelengths
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Blackbody Radiation
255?K
5780?K
Normalized blackbody spectra representative of
the sun (left) and the earth (right).
Wallace and Hobbs, p. 288
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Energy comes to earth in these wavelengths
Energy leaves the earth in these wavelengths
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Energy comes to earth in these wavelengths
Energy leaves the earth in these wavelengths
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Effect of Clouds
Clear sky conditions
Cloudy conditions
Ahrens 3rd Edition, p. 63
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Absorption Spectra of Atmospheric Gases
WAVELENGTH (micrometers)
Anthes, p. 55
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http//www.ems.psu.edu./Courses/earth002/0402G_M.h
tm
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Global Water Balance
Precipitation
Precipitation
Evaporation
Runoff
Ocean
Land
Earths annual water balance, (original) units
are 105 km3 of water per year. Huge quantities
of water are cycled through the atmosphere each
year. On the continents, precipitation exceeds
evaporation and the reverse is true for oceans.
Runoff from the continents balances the deficit
of the oceans.
Anthes, p. 47 (modified)
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Global Energy Balance
Incoming Solar Radiation
100
100
SPACE
Reflected Solar Radiation
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20
4
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ATMOSPHERE
Back-Scattered by Air
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Absorbed by H2O, Dust, O3
Reflected by Clouds
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Absorbed in Clouds
Reflected by Surface
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OCEAN and LAND
Based on Wallace and Hobbs, p. 321
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