Raindrop size distributions and their association with characteristics of clouds and precipitation during monsoon and post-monsoon periods over a tropical Indian station

Abstract

The raindrop size distributions (DSD) measured with the JW (Joss and Waldvogel) impact type of disdrometer have been utilized to study the characteristic features of precipitation during the monsoon and post-monsoon months over the tropical Indian station Pune (18.53°N, 73.85°E). Significant variations have been noticed in respect of raindrops during the two seasons. Larger raindrops are more in number during the post-monsoon rains whereas smaller and medium sized drops showed its prominent presence during the monsoon months for the same rain rates. This is mainly due to the convective nature of rainfall in the post-monsoon months, where intense convection, accompanied by strong updrafts lifts the smaller drops aloft thereby allowing the large drops to precipitate locally. The causative mechanisms/processes for the observed difference in DSD for the two seasons have also been discussed with the help of satellite data. At the same time, it has been found that the percentage of lower and middle level clouds are more during the post-monsoon months whereas the percentage of higher level clouds dominates the other two types of clouds during the monsoon period. The decreasing trend of cloud effective radius (CER) has also been noticed from the monsoon to post-monsoon months over the mentioned region.