The characteristics of precipitation drop size distribution in summer and winter in eastern Hubei province

The raindrop size distribution (DSD) is one of the fundamental parameters of microphysical character of precipitation. Comparative analysis of different rainfall types in summer and winter enhances the understanding of precipitation formation and evolution, 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. The potential causes of these differences and their impacts on the shape–slope parameter relationship (μ–λ) and the radar reflectivity–rainfall intensity (Z–R) relationships are thoroughly investigated. The results show that, in eastern Hubei, summer precipitation is dominated by convective rain under the influence of water vapor transport from the southern Indian Ocean, 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, with smaller D_m and larger N_w. In convective rain during summer, strong 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.