Quantitative Comparison of Disdrometer and Polarimetric Radar Measurements to Reveal Rain Microphysics during Meiyu Season in Eastern China

Joint polarimetric radar and disdrometer observations are, for the first time, used to characterize rain microphysics during the Meiyu season in Eastern China.First, the disdrometer-measured raindrop size distributions (DSDs) data are processed to refine the constrained gamma (C-G) model for DSD retrieval from polarimetric radar data (PRD) for rain events in Eastern China. It is shown that refined C-G DSD model performs better in retrieving rain DSDs than other two-parameter DSD models. Second, based on the DSD retrievals, the spatial distribution characteristics of Meiyu precipitation are investigated. Meiyu precipitation has widely spread stratiform with convection embedded. In convective region below freezing level, differential reflectivity (Zdr) ranged from 0 to 1.6 dB and correlated coefficient between horizontal and vertical polarization signals (ƒÏhv) were larger than 0.97 in convective core (reflectivity peak >45 dBZ). Therefore, the raindrop number concentration of convection is large (up to 10,000 #/m3) while the mass-weighted mean diameter is no larger than 2 mm. Meanwhile, decrease in correlated coefficient with increased in reflectivity and differential reflectivity around the 0 °C level indicated mixed-phase precipitation. DSD in stratiform were dominated by much lower concentration of drops, on the order of 100-1000 m-3 with the mass weighted diameter of 1-1.4 mm. Moreover, higher number concentration of drops was found in updraft region than that in downdraft region. Overall, the raindrop number concentration is higher and the mass weighted mean diameter is smaller than those of North American rain events with the same rainfall rate.