elevation of the sun. As the sun increases in elevation, the amount of diffuse radiation received in shade spots should increase. A given area of ground in a patch of sun may also receive greater amounts of solar radiation than it would in the open desert. For example, Rosenberg (1974) found areas near a tree shelterbelt to receive amounts of daily radiation equal to an area remote from the shelterbelt. Although shaded for several hours in the morning, the site near the shelterbelt received additional reflected energy off the shelterbelt in the late afternoon. Furthermore, Patten and Smith (1975) note that solar radiation can be extremely high (approaching the solar constant) when scattered cumulus clouds provide large amounts of diffuse radiation in addition to direct radiation. Such a phenomenon will possibly occur due to reflection off nearby collectors, and could have significant ecological effects. Although solar radiation under collectors will be greatly reduced on a daily basis, it may be intense at certain times of the day. Temperature Daytime air temperatures under heliostat fields and photo thermal and photovoltaic arrays will probably be only slightly lower or not significantly different than in the open desert. Air temperatures in shaded microhabitats are generally slightly cooler during the day (Patten and Smith 1973, Hanson and Ravzi 1977, Bajza et at. 1977), with the differences being more pronounced in the dry season (Patten and Smith 1974). Daytime air temperatures near the ground surface should be substantially cooler under solar collection arrays (Black and Veatch 1977); this has also been observed under large Sonoran Desert shrubs (Patten and Smith 1974). Also of potential importance in collector fields is the observation of Tuller (1973) that areas shaded from morning sun have a higher mean daily temperature than areas shaded from afternoon sun. In winter months, air temperatures may be warmer than the open desert due to reduced losses of thermal radiation. Night temperatures in areas shaded during the day are not as well documented. Bajza et at. (1977) observed nocturnal air temperature to be higher in a shaded microhabitat, evidently because the tree canopies which produced the shade also reduced the amount of escaping long-wave radiation at night.
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