Comparative study of summer and winter raindrop size distribution in eastern Hubei province

Raindrop size distribution (DSD) is a fundamental parameter describing the microphysical properties of precipitation. Comparative analysis of different rainfall types in summer and winter enhances the understanding of precipitation formation and evolution processes, thereby improving the accuracy of radar-based quantitative precipitation estimation (QPE). Based on Parsivel disdrometer observations from four sites in eastern Hubei during 2015–2018, the microphysical parameters were retrieved using a three-parameter gamma distribution function. Combined with ERA5 reanalysis and FY-2G satellite data, this study systematically analyzes the seasonal characteristics of DSDs for stratiform and convective rainfall, explores the potential causes of these differences and evaluate their impacts on the shape–slope parameter relationship (μ–λ) and the radar reflectivity–rainfall intensity (Z–R) relationships. The results show that, summer precipitation in eastern Hubei, is predominantly convective rain under the influence of water vapor transport from the southern Indian Ocean, and characterized by a larger mass-weighted mean diameter (D_m) and a smaller normalized intercept parameter (N_w). In contrast, winter precipitation is primarily stratiform rain under northwesterly flow, featuring smaller D_m and larger N_w. During summer convective rain, enhanced coalescence and breakup processes lead to significantly higher number concentrations N(D) of small and medium-sized raindrops than in winter. In stratiform rain, however, weaker updrafts and longer particle residence times in winter lead to higher concentrations of both small and large drops, while the N(D) of medium-sized drops is slightly lower than in summer. These microphysical differences also lead to significant regional variations in the μ–λ and Z–R relationships compared with other areas.