Differences in raindrop size distribution from southwest monsoon to northeast monsoon at Gadanki

Abstract

AbstractCharacteristics of raindrop size distribution (DSD) are studied during the southwest (SW) and northeast (NE) monsoon seasons using 4 1/2 years of DSD measurements made at Gadanki (13.5°N, 79.2°E) by an impact‐type disdrometer. The observed DSD is found to be distinctly different in the NE monsoon from that of the SW monsoon. The stratified DSD (based on rain rate) shows more small drops and fewer bigger drops in the NE monsoon than in the SW monsoon, particularly in the low rain rate regime. This feature is not an anomalous one, rather observed consistently in all the years. The diurnal variation of DSD (in terms of mass‐weighted mean diameter, Dm) plots in both monsoons show large values of Dm in the evening hours. Several possible reasons, from instrumental problems to geophysical mechanisms, for the observed DSD differences are examined. The wind field and the range of Dm values indicate that the DSDs in the SW and NE monsoons are continental and oceanic in nature, respectively. Further, high temperature and intense convective activity (vigorous updraughts) in the SW monsoon modify the DSD through evaporation, drop sorting, and collision‐coalescence processes. Copyright © 2009 Royal Meteorological Society