10%, microwave beam wandering and spreading due to atmospheric refraction may occasionally give rise to larger effects. It is possible to investigate the effects of the rectenna by studying the effects of land-use changes. Small temperature changes (of the order of 1°C) can be expected under light wind conditions. Changes in cloud populations can also be expected. Somewhat larger man-made dissipation rates over comparable areas have been associated with apparent anomalies in the distribution of rainfall. In hilly terrain, on scales smaller than the rectenna dimensions, di- urnally varying changes occur in the surface energy budget that are larger than the projected rectenna waste heat. It is therefore expected that the meteorological effects of a rectenna would vary from site to site, and the central maximum heat dissipation (approximately 16 W/m2) might become important in augmenting a naturally occurring topographic effect. Assessment of possible weather and climate effects over areas larger than the mesoscale should not be confined to the influence of the rectenna alone — it is necessary to consider the whole satellite power system in the context of the energy demand it is designed to meet. The overriding feature of the system is that the major inefficiency, the rejection of waste heat, is in space. Furthermore, there are no significant emissions of material into the troposphere during operation. b. Microwave Propagation. The atmospheric absorption of microwave energy at the proposed SPS frequency is negligible in clear air for the projected tropospheric path lengths of about 20 km. However, some absorption by condensed water (clouds and precipitation) would occur when storms entered the beam path. c. Atmospheric Electricity. Direct interactions with the atmospheric electric fields are not thought to be important at the proposed frequency. However, the mere physical presence of the rectenna might have some modifying influence on the occurrence and electrical behavior of thunderstorms over and around the rectenna. 4. MODEL CALCULATIONS In order to examine further the rectenna effects on local meteorological variables, a trial simulation using a three-dimensional, turbulence-closure model3 was made for a daytime, planetary-boundary-layer condition (constant potential temperature up to 650 m in height, then increasing with height at a rate of 3.5°C/km) with logarithmic wind profile up to 4 m/s and remaining constant above that. It was found that the increased roughness over the rectenna would considerable increase the surface heat flux (by a factor of 3.5) and friction velocity (by a factor of 1.9) at the center of the site in comparison with values located at the upstream boundary. The numerical values given in the parentheses are valid for the case of dry convection and little temperature contrast between the rectenna and the surrounding surface. Inclusion of 8 W/m2 of waste heat would cause a surface temperature perturbation of less than 0.1°C.
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