In summary, preliminary estimates of the local and mesoscale weather and climate effects of construction of a rectenna are that they are generally small but detectable in some instances. The major immediate issue is to confirm these estimates by the most convincing methods now available. In an enterprise of the magnitude of the SPS any other approach to a question which might have an economic impact on the population at large, and which certainly impacts its peace of mind, would be inadequate. A second issue is that the possibilities of modifying weather and climate change by constructional manipulations not affecting system efficiency should be explored. A third is that some atmospheric effects are likely to be site specific. Investigation of these effects by the best available methods should be part of the assessment of the environmental impact of rectenna construction at each site considered . 3A.2 MICROWAVE PROPAGATION EFFECTS It has been concluded that the passage of the microwave beam through the atmosphere will produce no significant meteorological consequence (Ref. 3.16). Much attention was focused, during the panel discussions, on the possible effects of the natural atmospheric conditions on the microwave beam propagation and the associated power beam and pilot beam stability problems. Variations in the refractive index of the atmosphere and the presence of hydrometeors in the atmosphere cause refraction, scattering and absorption of electromagnetic waves. At 2.45 GHz the refractive index of air at fixed pressure depends mostly on water vapor and temperature. In the presence of convective or turbulent air motions a spectrum of atmospheric refractivity develops. The refractivity variations can lead to beam wandering and spreading. The scattering and absorption by hydrometeors depends on their size, shape, number, concentration, and composition. If these properties are specified, calculations can be made of atmospheric attenuation and of the spreading of the beam. In considering the effects of natural atmospheric conditions, it is convenient to examine various possible contributions from the boundary layer, cloud systems, jet stream turbulence and stable layers.
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