Microphysical characteristics of clouds and precipitation during pre-monsoon and monsoon period over a tropical Indian station

Abstract

Characteristics of clouds and precipitation during the pre-monsoon (PM) and monsoon months (MM) have been examined in the present study over the tropical station Kolkata (22.65°N, 88.45°E), which is located in the eastern part of India. Satellite data of clouds for the years 2005–2007 and raindrop size distributions (DSD) derived from ground-based Disdrometer for the years 2005 and 2006 for PM and MM has been considered here. Results shows that lower and middle level clouds dominate in the pre-monsoon season and the higher-level clouds are predominant in the monsoon season over the mentioned region. Correspondingly the cloud effective radius value also increases from the pre-monsoon to the monsoon months. The impact of aerosols and moisture plays a vital role in such changes. The characteristics of raindrop size distribution for the two seasons also showed that larger drops are more prevalent during pre-monsoon season whereas the smaller drops are present in larger number in the monsoon months. This is mainly due to the convective nature of rainfall in the pre-monsoon months, where intense convection, accompanied by strong updrafts modifies the raindrops. Thus pre-monsoon (monsoon) season over Kolkata region is characterized by lower/middle level (higher level) clouds, smaller (larger) cloud drop size and larger (smaller) raindrop size at the surface.