Rain Microphysics Associated with Continental, Oceanic, and Orographic Regions of India during Wet and Dry Spells

The dominant microphysical processes responsible for differences in the mass-weighted mean diameter ( D m ) of deep and shallow rain during wet and dry spells of southwest monsoon (SWM) and northeast monsoon (NEM) over continental, oceanic, and orographic regions of India are inferred from Global Precipitation Measurement (GPM) dual-frequency precipitation radar (DPR) measurements made between 2014 and 2022. The deep precipitating systems’ D m shows oceanic and continental nature during wet and dry spells of SWM and NEM. The dry spells of SWM over northwest India, all the spells except the wet spells of NEM over southeast peninsular India, and dry spells of NEM over northeast India show continental rain clusters and others show maritime rain characteristics. Mean D m of deep systems at various rain-rate intervals shows marked intraseasonal variations over northwest India, central India, and foothills of the Himalayas during SWM and over the Western Ghats, southeast peninsular India, and northeast India during the NEM. Though D m is larger in SWM than in NEM at seasonal scale, the dry spells of NEM show largest D m than in other spells in SWM and NEM. The observed near-surface D m differences between the wet and dry spells of SWM and NEM are seen from 1.5 km below the melting layer and are magnified during the descent of raindrops by the microphysical processes over all the regions except for southeast peninsular India and Myanmar coast during the SWM dry spells. Below the melting layer, collision–coalescence and breakup processes are considerable in the deep precipitating systems, and only the collision–coalescence process (>95%) dominates in shallow rain over all regions. Significance Statement Rainfall exhibits considerable intraseasonal variations triggering wet (or active) and dry (or break) spells during both southwest monsoon (SWM) and northeast monsoon (NEM). Significant progress has been made in understanding the wet and dry spells characteristics, while least explored is the raindrop size distribution (DSD) characteristics, which is the fundamental property of precipitation. At seasonal scale, DSDs show numerous smaller raindrops in NEM than in SWM; contrastingly, at intraseasonal time scales, abundant bigger raindrops are found in NEM dry spells than in SWM spells. At the seasonal scale, DSD characteristics show maritime precipitation features over India; however, SWM dry spells over northwest India, all the spells except the NEM wet spells over southeast peninsular India, NEM dry spells over northeast India show continental and others indicate maritime rain characteristics.