Seasonal variation of raindrop size distribution in south India obtained from disdrometer measurements supported by wind-profiler observations

South India has three distinct rainfall seasons, namely south-west (SW) monsoon, north-east (NE) monsoon and transition periods. We have been conducting wind profiler and disdrometer observations in Gadanki, A.P. where National MST Radar Facility (NMRF) of India has a comprehensive atmospheric radar observation site. From a long-term observation between 1997 and 2000, it is found that there is a significant difference in raindrop size distributions (DSDs) between the SW and NE monsoon periods; the SW monsoon rainfall generally has much larger number of large raindrops than in the NE monsoon. Rainfall type dependence is not as clear as those obtained in tropical Pacific ocean, however. This result suggests that the radar estimation of rainfall rate in tropical monsoon areas needs a careful thought in the modeling of DSD or Z-R relations, such as those used for TRMM Precipitation Radar. The seasonal variation of DSD is also analyzed using vertical profiles of rainfall observed by an L-band wind profiler collocated with the disdrometer. Consideration is given to the possibility of correlating DSD properties with the vertical pointing Doppler radar data.