The interseasonal features of precipitation microphysics over Thiruvananthapuram and Kolkata - the two tropical stations of Indian sub-continent

Abstract

A comparative study of precipitation microphysics along with the possible causative mechanisms for the inter-seasonal variation of raindrop size distribution over Thiruvananthapuram and Kolkata – the two tropical stations of Indian sub-continent has been highlighted in this paper. In addition to the contrasting geographical and climatic variations, the importance of the two locations lies in the fact that the rainfall over Thiruvananthapuram represents the Arabian Sea branch of south-west monsoon while that over Kolkata represents the Bay of Bengal branch. The study reveals a distinct domination of raindrops of diameter 2 mm and above for the pre-monsoon months (March–May) over Kolkata with respect to Thiruvananthapuram, while for the monsoon months (June–September), no such appreciable differences are noticed. Correspondingly, the continental and maritime clouds also show their contrasting impacts in the rainfall microphysics during these inter-seasonal phases for the two locations. It has been observed that rainfall evolving from the continental clouds during the pre-monsoon period over Kolkata produces distinct diurnal variation of rainfall occurrences, which are also associated with the presence of raindrop of diameter 3 mm and above. Correspondingly, such variations are absent for the maritime clouds which dominate the monsoon rainfall for both the locations. Thus it can be said that the nature of clouds along with the surface temperature plays an important role in the varying microphysics of precipitation during the inter-seasonal phases of monsoon over these two cities of India.