Characteristics of the Raindrop Size Distribution during the Rainy Season in Beijing, China

Characteristics of raindrop size distributions (DSDs) during the rainy season of 2017 in Beijing, China, are studied comprehensively for the first time with a second-generation ground-based PARSIVEL disdrometer. It will be helpful to improve the accuracy of microphysical parameterizations and remote sensing retrieval methods regionally, since the climatological characteristics of precipitation in Beijing is affected by many factors, including the unique orographic conditions and high aerosol concentrations, among others. Based on measurements at 1-min intervals, samples with rain rates lower than 5 mm h^-1are the most frequent whereas the remainder account for the bulk of the rainfall amount. Composite DSD shapes for eight different rain-rate classes are similar with widths that broaden with increasing rainfall intensity. An upper threshold of 10 mm h^-1was found for stratiform rain rates independent of rain-type classification scheme. Compared with monsoon precipitation in Eastern China, the mean value of mass-weighted mean diameter (D_m) is much smaller for stratiform rain but much larger for convective rain, with significantly higher variabilities of D_mand generalized intercepts (N_w) for both rain types. This may be attributable to the intensive cold-cloud processes and high aerosol concentrations in Beijing. Our power-law relationship between the mass spectrum standard deviation (σ_m) and D_malmost coincide with the result reported by Williams et al. (2014). Assuming gamma-shaped DSDs, the σ_m-D_mrelationship is transformed to constrained-gamma DSD model, or μ-Λrelationship, which can better the microphysical parameterizations in numerical models. The X-band dual-linear polarization radar parameters, including Z_h,Z_DR, and K_DP, are derived by the disdrometer observations using the T-matrix scattering method. Comparisons between quantitative precipitation estimators reveal that R(Z_h, Z_DR) has the best performance with the highest correlation coefficient and lowest standard deviation, followed byR(K_DP, Z_DR),R(K_DP), and R(Z_h). This study provides reliable bases for the evaluation and application of X-band dual-polarization weather radar network in Beijing in future.