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
The 2nd Law of Thermodynamics
No transformation of energy can be 100% efficient
Energy Flow
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.
The r2 Law
How much energy one
receives depends on how far
you are from the source
Energy Flow
Energy Balance - No Atmosphere
apR
S
2
4pR T
2
pR S
2
4
Incoming SW Radiation = Reflected SW Radiation + Outgoing Longwave
pR2 S
=
S (1 - a) = 4Tp4
apR2 S
+
4pR2 T4
R = Earth’s radius
S = 1370 Wm-2
a = 0.3
 = 5.67 x10-8 Wm-2
T = 255oK
Our sun is really hot and emits most of it’s
energy at shorter wavelengths. The earth is
relatively cool and emits energy at longer
wavelengths
Blackbody Radiation
5780K
255K
Normalized blackbody spectra representative of the sun
(left) and the earth (right).
Wallace and Hobbs, p. 288
Energy leaves the earth in these
wavelengths
Energy comes to earth in these
wavelengths
Energy leaves the earth in these
wavelengths
Energy comes to earth in these
wavelengths
Effect of Clouds
Clear sky conditions
Ahrens 3rd Edition, p. 63
Cloudy conditions
Absorption Spectra of Atmospheric Gases
WAVELENGTH (micrometers)
Anthes, p. 55
http://www.ems.psu.edu./Courses/earth002/0402G_M.htm
Global Water Balance
Precipitation
Precipitation
100
21
79
13
Evaporation
87
8
Runoff
Land
Ocean
Earth’s 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)
Global Energy Balance
Incoming Solar Radiation
100
SPACE
Reflected Solar Radiation
6
ATMOSPHERE
20
4
100
= 30
Back-Scattered by Air
16
Absorbed by
H2O, Dust, O3
Reflected by
Clouds
= 19
3
Absorbed
in Clouds
Reflected by
Surface
51
OCEAN and LAND
Based on Wallace and Hobbs, p. 321
51