Abstract Understanding the variability of rainfall microphysics across different climatic regimes is crucial for improving radar and satellite rainfall retrievals, as well as cloud microphysics parameterizations in numerical models. This study analyses the variability in raindrop size distribution (DSD) during the Indian summer monsoon (June–September, JJAS) over coastal, windward, and leeward regions of the Western Ghats using Joss–Waldvogel disdrometer observations. Principal Component Analysis (PCA) is employed to objectively identify dominant modes of DSD variability and group rain events with similar microphysical properties. Despite the regional differences in DSD characteristics, PCA reveals four common modes (Group 1–4) of DSD variability across all regions, although the frequency and dominance of each mode vary spatially. Group 1 is characterized by a broader DSD distribution with a larger median drop diameter ( D 0 ), higher values of liquid water content (LWC) and rain rate ( R ), typical of intense convective precipitation. Group 2 contains narrow DSD spectra with smaller D 0 and lower values of LWC and R , indicative of weak stratiform rainfall. Group 3 exhibits the smallest D 0 , moderate LWC and highest raindrop concentrations, likely formed by collision–coalescence and breakup processes found in warm rain systems. Group 4 appears to be transitional between Group 1 and Group 2 and is most likely associated with stratiform rainfall. A clear regional variation in DSD modes is observed: the coastal region predominantly exhibits Groups 3 and 4 (maritime warm rain and stratiform), the windward slope is mainly characterised by Group 3 (orographic warm rain), and the leeward side shows a higher occurrence of Groups 1 and 4.
Krishna et al. (2026) studied this question.