Figure 3-10. Path of a Straight Line Ray from a Geostationary Satellite to a Midlatitude Receiving Site satellite ATS-3. Throughout the period of observation the elevation angle was close to 41 degrees. The daily variation of solar radiation gives rise to a typical variation in TEC which changes slowly with month and season. However, under geomag - netically disturbed conditions marked departure can occur from the usual diurnal change. The Faraday rotation at a midlatitude rectenna site under quiet conditions will also follow the same cyclical pattern as the TEC. Estimates of and the polarization "loss", based on mean monthly diurnal TEC measurements, are shown in Figure 3-11 for a typical Northeast (40°N) location. The polarization loss occurs if the rectenna dipoles (Section 9) are not aligned with the incident direction of the electric field. It is computed by assuming that the cross-polarized component is totally reflected or scattered by the rectenna structure. It is clear that Faraday rotation under geomagnetically quiet conditions produces insignificant polarization losses. 3.5.3 MIDLATITUDE GEOMAGNETIC STORMS AFCRL has also compiled an atlas of TEC variations during geomagnetically disturbed periods. (16) particularly severe storm has been selected to estimate the maximum polarization loss under disturbed conditions. As the result of a magnetic storm on 8 March 1970 a sudden enhancement of 66 percent above the
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