Simultaneous measurements of microwave fading and lower atmospheric conditions were carried out in Georgia in 1986 as a part of the continuing effort to study the line-of-sight digital radio performance. Acoustic sounding was a principal means of exploring the mechanism that causes dispersive fading. It was found that dispersive multipath fading occurs during nights with strong radiation inversion accompanied by a subsiding air mass. Subsidence inversion causes dispersion, and the origin of the air mass affects the mean received power level under multipath propagation conditions. When the height of the nocturnal boundary layer coincides with the height of the ground-based radiation inversion layer and is at 100-150 m, fading is heavy, active, and dispersive for a 57-km path with both transmitting and receiving antennae at 60 m above grade. Case studies of the significant episodes are presented, and the statistics of the different types of fading associated with the types of meteorological conditions are summarized for the 5-month study period. 133 134 LEE: MICROWAVE FADING AND ATMOSPHERE STRUCTURE FADING AND ATMOSPHERE STRUCTURE 139 Fig. 7. 400 300 200 100 ß ß ß / / 400 300 200 lOO LEE: MICROWAVE FADING AND ATMOSPHERE STRUCTURE radio systems as a function of path length and frequency, Bell Syst. Tech. J., 50(7), 2375-2398, 1971. Schiavone, J. A., Microwave radio meteorology: Diurnal fading distributions, Radio Sci., 17(5), 1301-1312, 1982. Sharpless, W. M., Measurements of the angle of arrival of microwaves, Proc. IRE, 34, 837-845, 1946. A review, Radio Sci., 16, 609-629, 1981. Tatarski, V. I., The Effect of the Turbulent Atmosphere on Wave Propagation, translated from Russian, 471 pp., Israel Program for Scientific Translations, Jerusalem, 1971. Vigants, A., Temporal variability of distance dependence of ampli-tude dispersion and fading, paper presented at ICC '84, Inst. of Electr. and Electron. Eng., Amsterdam, 1984. Webster, A. R., Angle-of-arrival and delay times on terrestrial line-of-sight microwave links, IEEE Trans. Antennas Propag., AP-31(1), 12-17, 1983. Webster, A. R., and A.M. Scott, Angles-of-arrival and tropospheric multipath microwave propagation, IEEE Trans. Antennas Propag., AP -35(1), 94-99, 1987. Stephansen, E. T., Clear air propagation on line-of-sight radio paths:
A numerical model of a cooling tower plume is employed to study the possible atmospheric effects of thermal plumes from natural draft dry cooling towers. Calculations are performed for both single and multiple towers, each of which can dissipate the waste heat from a nominal 1000 MWe power generating unit, and the results are compared with those for wet cooling towers associated with plants of the same generating capacity. Dry cooling tower plumes are found to have a higher potential for inducing convective clouds than wet cooling tower plumes, under most summertime meteorological conditions. This is due to the fact that both the sensible heat and momentum fluxes from a dry tower in summer are approximately one order of magnitude larger than those from a wet cooling tower.
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