MEASUREMENTS OF RAIN DROP SIZE DISTRBUTION FROM RADAR REFLECTIVITY AND ASSOCIATED RAIN ATTENUATION OF RADIO WAVES

摘要

Radar measurements of rainfall at different climatological conditions have been taken into account emphasizing rain rate and associated radar reflectivity. It is observed from the analysis that the reflectivity measurement is being consistent at high rain intensities. From the knowledge of radar reflectivity, the rain drop size distribution is examined. The most probable drop size diameter and rain rate have been calculated wherefrom it appears that the most probable rain drop size vary exponentially with radar reflectivity and also with rain rate. The theoretical model implemented by using the measured rain drop sizes over the tropical sites also show similar kind of variation. For estimating rain attenuation two important parameters, viz., the point rainfall rates and the vertical and horizontal structures of rain have been considered. The elevation angle we have chosen is ~ 560 as most of the stations in India have that value of elevation angle with geostationary satellite. Taking the frequencies 11 to 14 GHz separately and 00 C isotherm height as 5.0 km, the effective rain height values are determined. The attenuation of radio waves due to rain are calculated for different rain rates assigning different ?-values. The attenuation is found to vary significantly with the ?-values. Also the attenuation curves are closer when the ?-values are of low order. An increase in attenuation with the ?-values is found to be more prominent for higher rain rates.