A more realistic simulation was performed for a potentially unstable boundary layer with light winds over moist, flat ground.4 Such a situation is conducive to the natural formation of cumulus clouds without precipitation. The simulation indicated that, excluding the effects of albedo changes, the major cause of the perturbation is again the change in surface roughness rather than the release of waste heat. Air and soil temperature decreased during the daytime and increased only marginally at night. The increased mechanical mixing resulted in increased evaporation and absolute humidity, increased cloud amount, and decreased cloud-base height. The decrease in solar radiation resulting from the increase in cloud amount is greater than the waste heat term. Cloud modification would be expected to be quite different if the roughness had not been changed. The results found in this case (moist convection) are considerably different from those in the dry convection case above. A preliminary analysis of the problem of rectenna albedo and its diurnal variation indicated that differences between the rectenna albedo and that of the surrounding surface may be most significant factor.4 These effects need to be quantified in future work. Information regarding the amount of microwave absorption per unit path length as a function of rainfall rate is available.5 With the most extreme rainfall rate of 254imn/hr as an example, the attenuation at the proposed 2.45-GHz frequency is estimated to be about 0.063 dB/km. At the proposed maximum power density of 230 W/m2, the absorbed microwave power inside the storm would be approximately 3.2 x 10""3 W/m3, which is approximately two orders of magnitude smaller than the release rate of the buoyant energy of a typical cumulus cloud. It is reasonable to conclude that the absorption of SPS microwave power by a storm will have no significant influence on cloud dynamics and thermodynamics and the associated precipitation. 5. CONCLUSIONS Analyses and model simulations in some chosen site situations and meteorological conditions indicate that the meteorological effects of the construction and operation of a rectenna are small, particularly outside the boundary of the structure. From weather and climate points of view, installation of an SPS rectenna seems likely to have effects comparable with those due to other nonindustrial land-use changes covering the same area. The absorption and scattering of microwave radiation in the troposphere would have negligible atmospheric effects. It seems clear that rectenna-related meteorological effects are not a critical factor in the overall environment impact of the SPS. However, there are some remaining areas of detail that should be investigated; they are concerned with the radiative properties of the rectenna structure, the possible ''triggering” of convective instability under certain meteorological conditions, and the nature of the terrain at and near the structure.
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