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.

本文重点介绍了印度次大陆的两个热带站蒂鲁文南特布勒姆和加尔各答的降水微物理以及雨滴大小分布季节性变化的可能原因机制的比较研究。除了地理和气候差异的对比，这两个地点的重要性还在于，蒂鲁文南特布勒姆上空的降雨代表西南季风的阿拉伯海分支，而加尔各答上空的降雨则代表孟加拉湾分支。研究表明，在季风前几个月（3 月至 5 月），对于蒂鲁文南特布勒姆，加尔各答的雨滴明显占主导地位，而季风月（6 月至 9 月）则没有注意到这种明显差异。相应地，在这两个季节间的阶段，大陆和海洋云也显示了它们对降雨微物理的对比影响。已经观察到，在加尔各答的季风前期期间，从大陆云演变而来的降雨会产生明显的降雨日变化，这也与直径 3 毫米及以上的雨滴的存在有关。相应地，在这两个地点主导季风降雨的海洋云层不存在这种变化。因此可以说，在印度这两个城市的季风季节间阶段，云的性质和地表温度对降水的微物理变化起着重要作用。