6.J2 humidity will be kept near 60%, clouds are infrequent. Therefore, virtually no radiation is reflected away due to clouds. Also, because of the small amount of atmosphere, radiation directly absorbed into the atmosphere (about 20% on earth) is negligible. Though plants absorb over 95% of incident infrared radiation of the longer wavelengths (6.Jl), about 15% of the radiation, or 93 cal/cm2-day, is reflected off the fields. This leaves 526 cal/cm2day to be distributed to the soil, water and air (6.J4). On Earth nocturnal radiation is the net upward flux of long-wave radiation at the surface, approximately 180 cal/cm2-day with clear skies. This net longwave radiation proceeds night and day. At night, it is partially offset by a downward f~ux of heat from the atmosphere, but the nighttime cooling of the ground material must be about 75 cal/cm 2 -12 hours. The daytime heating of soil offsets this amount of heat, or on the order of 75 cal/cm 2 -12 hours (6.J5}. From 5 a.m. - 7 p.m. Depth in Soil Surface 5 cm 10 cm 15 cm 20 cm 25 cm in Leipzig on a summer day 6T,°C Density (wet soil) 1.3 g/cm 3 14 Specific Heat .4 cal/g-deg 10 5 2 1 0 Heat or ~T 25xl.3x4x5 70 cal/cm2-day 5 cal/cm2-hr (pronounced time lag with depth) Hence a rough figure for heating of wet soil over the 18-hour colony day is 90 cal/cm 2 -18 hours (day) (6.J5). Approximately 35% of remaining heat available: .35 (619 - 93 - 90) = 153 cal/cm 2 -day goes to evaporate water. This is obviously a function of the wetness of the surface. Left to heat the atmosphere is 283 cal/cm 2 -day. Therefore, about 25% of the incoming energy, or 99 watts/m 2 is available for vaporization and evapotranspiration.
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