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FIGURE 14.5 Annual mean radiation measured by satellite in 1988 at the top of the atmosphere as a function of latitude for incoming absorbed short-wavelength radiation and emitted outgoing long-wavelength radiation (adapted from Trenberth and Solomon, 1994).

at the top of the atmosphere, derived from satellite measurements in 1988, as a function of latitude (Trenberth and Solomon, 1994). Around the equator, a great deal more incoming solar energy is absorbed than is emitted at the longer wavelengths, whereas the opposite is true at high latitudes. As a result, low latitudes are warmed and high latitudes cooled, causing heat transport from the equator toward the poles by the atmosphere and oceans.

2. Radiative Transfer Processes in the Atmosphere a. Macroscopic View

The spectral distribution of the radiation emitted by the earth's surface is determined by its temperature; i.e., the emission is that of a blackbody at an average temperature of 288 K. Thermal emission at the earth's surface produces a net upward flux of energy. Let us denote upward energy fluxes by F+ and downward fluxes by F~. The transfer of radiant energy in the troposphere can be thought of as occurring between vertical layers in the atmosphere as shown in Fig. 14.6a. The total energy flux (Fnc[) crossing a plane at a given altitude z is the difference between the upward and downward fluxes; i.e., Fnel = F+ — F~. As shown in Fig. 14.6b, the flux of light energy through a volume of air is determined by a combination of transmission, absorption, scattering both in and out of the "beam," and thermal emission from the gas molecules (shown on a molecular level in Fig. 14.6c and described in more detail later).

FIGURE 14.5 Annual mean radiation measured by satellite in 1988 at the top of the atmosphere as a function of latitude for incoming absorbed short-wavelength radiation and emitted outgoing long-wavelength radiation (adapted from Trenberth and Solomon, 1994).

Latitude

Latitude p3-p2-p1

F3+1

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