Abstract
Abstract
Through dedicated observations with a Joss–Waldvogel RD-80 disdrometer at Dumdum (22.65°N, 88.43°E) and an S-band Doppler Weather Radar at Kolkata (22.57°N, 88.35°E), this study characterises drop size distribution (DSD) evolution through the life-cycles of nine convective storm events spanning four seasons (October 2024 to April 2026) over the Gangetic plains of eastern India—a region whose precipitation microphysics remain poorly documented. Storm phases (developing, mature, and dissipating) are objectively defined by rain rate evolution and verified against plan position indicator radar imagery. A dataset of 1210 phase-classified one-minute DSD records alongside 128 radar volume scans is analysed. Phase-specific Z–R relationships are: Z = 887R¹·⁶² (developing, R² = 0.891), Z = 840R¹·⁶⁶ (mature, R² = 0.857), and Z = 1021R¹·⁶⁰ (dissipating, R² = 0.868); the overall relationship Z = 959R¹·⁶² (R² = 0.882) is consistent with a four-year climatological value of Z = 870R¹·⁵⁹ (n = 138,420). Radar–disdrometer comparison yields a systematic calibration bias of − 10.0 dBZ. Quasi-vertical profile analysis reveals seasonal bright-band height variation from 3.2 km (winter) to 5.8 km (post-monsoon), directly linking melting-layer depth to surface DSD contrasts through warm-rain column depth. Independent QPE validation demonstrates that the mature-phase Z–R achieves the best performance (RMSE = 3.04 mm, bias = + 21%), reducing Marshall–Palmer overestimation by an order of magnitude. The phase-aware QPE approach and the calibration methodology are transferable to other India Meteorological Department S-band radar sites across the Gangetic plains.