Comparative analysis of raindrop spectral characteristics of two extremely heavy precipitations in Guangxi

To better understand the differences in microphysical characteristics of heavy rainfall events in Guangxi, this study utilized conventional meteorological observations, disdrometers, Doppler radar data, and ERA5 reanalysis to examine two heavy rainfall cases: a short-duration intense rainfall event in Guilin on May 22, 2023, and a long-lasting rainfall event in Beihai on June 8, 2023. The synoptic background, radar echo features, and ground-based raindrop size distributions of both events are analyzed. The results are as follows. (1) The short-term heavy rainfall in Guilin resulted from the interaction of a low vortex, shear line, and cold air intrusion.Convection was strong and well-developed, with a fully developed cold cloud process.Solid particles, including large hail, were inferred to exist within the clouds. In contrast, the prolonged heavy rainfall in Beihai was primarily associated with a tropical low-pressure system. Convection was relatively weaker, with strong echo centers located below the 0 °C layer, indicating dominance by warm cloud precipitation. (2) The convective precipitation raindrop spectrum in Guilin exhibited larger mass-weighted mean diameter (D_m) and lower generalized intercept parameter (N_w), characteristic of continental convective precipitation. By comparison, the convective cloud precipitation spectrum in Beihai showed smaller D_m and higher N_w, typical of oceanic convective cloud precipitation. (3) In Guilin, solid particles in cold clouds melted into larger-diameter droplets.Additionally, collision and coalescence processes in warm clouds facilitated the formation of equilibrium raindrop spectra. Nearly 80 % transitional spectra indicated that the collision–fragmentation process significantly altered the distribution of raindrop sizes. In Beihai, solid precipitation particles in cold clouds mainly contributed small-size particle spectra. Although warm clouds allowed sufficient time for collision and coalescence mechanisms, the proportions of equilibrium and transitional spectra were much lower than those in Guilin, suggesting a weaker role of the collision–fragmentation process.