solar storms. During these periods, the magnitude of depolarisation will increase with higher latitudes, since the path of the microwave beam through the depolarising layers will be longer. More intensive investigations are required for this subject to get an idea of the magnitude of these implications. II.1.5.3 Attenuation of the RF-Beam by the Atmosphere and the Ionosphere Nearly all attenuation is due to molecular absorption of RF-power in the troposhere. Special literature reports attenuations of about 10 % under worst conditions. These conditions occur at very heavy thunderstorms with wet hail and storm cell hights of 1 km. Statistical investigations show very short times of the year with such bad weather in the proposed U.S. rectenna sites. Half of the U.S. rectennas must be located near the coast since 50 % of the U.S. population lives within a 80 km coastline. A comparison of rainfall in these areas with the investigated European area shows no substantial differences. Weather conditions, however, have to be considered with the selection of every rectenna site because of microclimatic variations compared with the statistical weather data of Western Europe. II.1.5.4 Impacts of the RF-Beam on the Atmosphere and the Ionosphere Increased impacts on the ionosphere due to higher latitudes will be treated in the sub-section II. 1.5.6. A slight increase in atmospheric temperature will occur due to longer absorption paths. However, we doubt whether this increase is measurable in significant amounts and whether this increase could influence the weather in those regions because of the relatively small amounts of power which will be fed into large areas.
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