Thermodynamics and the Flow of Heat through the Climate System - Climate Dynamics - page 104

In the global mean, the net radiative heating is zero for an equilibrium cli-
mate (Eq. 5.8), but it is hard to believe that when examining Figure 5.9a be-
cause the projection enlarges the surface area at high latitudes. The Mollweide
projection shown in Figure 5.9b plots surface area accurately and shows more
clearly that the radiation surplus in the tropics balances the radiation deficit in
high latitudes.
Given the distribution of the net radiative heating at the top of the atmo-
sphere shown in Figure 5.9, how is it that the tropical climate is not constantly
warming with time, and the high latitude climate cooling? Why is the climate
system (relatively) stable in the presence of large net radiative heating in the
tropics and radiative cooling at high latitudes at the top of the atmosphere?
The answer is that heat is redistributed within the climate system by atmo-
spheric and ocean circulation systems.

OBSERVED DISTRIBUTION: SURFACE

For the climatology, with no temperature trend, and combining the terms that
represent the redistribution of heat within the land or ocean surface, we can
rewrite Eq. 5.22 as

0 =+−−−− S F THHF εσ

4

(5.29)

ABS BACK S S L SFC

where

S =− (1 α ) S and F =+ F F .

ABS S INC SFC HV

The S ABS climatology is plotted in Figure 5.10. Values near the equator are three
to four times greater than those near the poles. This difference is partly due to the
decrease with latitude of the solar flux incident at the top of the atmosphere ( Fig.
5.5a) and partly due to albedo effects associated with the angle of incidence (Fig.

90°N

60

60 60

60

60°N

120 120

120

120

180 180

180

30°N

180

180

180

180

240

Equator

180

240

240

30°S

180 180

180

180

180

180

120

120

120

120

60°S

60

60 60 60

90°S

0° 30°E 60°E 90°E 120°E 150°E 180° 150°W 120°W 90°W 60°W 30°W 0°

Figure 5.10 Solar radiation absorbed at the surface. Contour intervals are 20 W/m 2 .