Global Absorption and Emission of Radiation

In Chapter 3 we examined the interaction of incoming solar radiation in the UV and visible regions of the spectrum with atmospheric gases, which drives atmospheric photochemistry. This incoming solar radiation 

FIGURE 14.1 Solar flux outside the atmosphere and at sea level, respectively. The emission of a blackbody at 6000 K is also shown for comparison. The species responsible for light absorption in the various regions (03, H20, etc.) are also shown (adapted from Howard el al., 1960). 

FIGURE 14.2 Global average mean radiation and energy balance per unit area of earth s surface. The numbers in parentheses are the energy in units of W m 2 typically involved in each path (adapted with permission from IPCC U996), with numbers from Kiehl and Trenberth (f997)). 

The net absorption of 235 W m-2 by the earth s surface and atmosphere leads to heating and hence to 

Clearly, 254 K is much colder than the typical temperatures around 288 K (15°C) found at the earth s surface. This difference between the calculated effective temperature and the true surface temperature is dramatically illustrated in Fig. 14.4, which shows the spectra of infrared radiation from earth measured from the Nimbus 4 satellite in three different locations, North Africa, Greenland, and Antarctica (Hanel et al., 1972). Also shown by the dotted lines are the calculated emissions from blackbodies at various temperatures. Over North Africa (Fig. 14.3a), in the window between 850 and 950 cm-1, where C02, O-, HzO, and other gases are not absorbing significantly, the temperature corresponds to blackbody emission at 320 K due to the infrared emissions from hot soil and vegetation. 

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