seasonally with latitude. Column 1 of Table 25 gives the daily mean value of undepleted solar radiation for the winter and summer solstice as a function of latitude for the Northern Hemisphere. In higher latitudes the seasonal variations are great. Thus, at 60 degrees, the range is from 24 to 465 W/m2, while at 20 degrees it varies from 280 to 420 W/m2. TABLE 25 SOLAR ENERGY Annual Range in Daily Mean Range of Mean Annual Net Latitude Undepleted Solar Radiation Radiation (degree) (W/m2) (W/m2) 60 24-465 26- 52 50 82-445 40- 65 40 140-440 52-100 30 220-430 75-130 20 280-420 100-150 Relatively little of the solar energy reaching the surface is expended in work. Some is lost as reflected solar energy, and some is reradiated as IR energy given off by the atmosphere or by the warm surface. The net radiation is the difference between solar insolation and the reflected, visible, and reradiated IR energy. It has been estimated for several locations on the earth by Budyko (49). Representative values of the annual mean net radiation are shown in column 2 of Table 26. It will be seen that these values are very large compared to the estimated energy loss from the receiving antenna. Thus, at 60 degrees the range is from 26 to about 52 W/m2, while nearer the equator at 20 degrees it varies from about 100 to 150 W/m2. These net radiation values are large compared to. the estimated energy losses of the receiving antenna. Since it is unlikely that a large percentage of the energy lost from the antenna will, in fact, be absorbed by the ground, the effect on the net radiation at the site will be much less than the relative values of the local net radiation and the estimated heat losses imply. This is best illustrated in the next section where the total environmental energy fluxes for representative environments with the quantity of energy added by the presence of a receiver are compared. c. Factors Determining “Environmental Temperature” Examination of Table 25 convincingly supports the arguments that the mean antenna losses are low, but there are worst possible situations that might be encountered; e.g., winter when the solar insolation is lowest, and nighttime, when there is no sun at all. Furthermore, although net radiation and solar insolation are important factors in determining the heat load impinging on local flora and fauna, they are not, in fact, of primary direct importance in determining what might be called the “environmental temperature.” This is due to the fact that such organisms actually intercept both incoming solar radiation from the sky and outgoing solar radiation that is reflected from the ground and other reflecting surfaces. In addition, thermal radiation - the incoming and
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