The microphysical characterization analysis of a supercell hailstorm

Based on the precipitation phenomenon instrument, CINRAD/SA-D dual-polarization weather radar, ground automatic stations, disaster surveys, and ERA5 data, the environmental conditions for a supercell hailstorm event were analyzed, the reliable observational data on the size distribution of hail were obtained by the particle identification technology, and the hail spectrum distribution was fitted. The study investigated the relationship between the ground particle spectrum distribution in different regions and stages of the hailstorm and the parameters of dual-polarization radar, gain an in-depth understanding of the microphysical processes, thermodynamics, and dynamics of supercell hailstorms.The results indicate that: (1) the hailstorm was jointly influenced by an upper-level trough and a surface convergence line, it is a right-moving supercell storm generated in a low-convective effective potential energy(CAPE) and strong vertical windshear environment, leading to disastrous large hail, localized heavy rainfall, and strong winds; (2)The identified hail particle size distributions in both Gaotang and Changqing both exhibit a monotonically decreasing pattern, and the Gamma distribution shows a significant fitting advantage for hailstones with a diameter≥5mm; due to the inclusion of graupel particles with a diameter <5mm, the intercept parameter N0 is generally larger than in previous studies; the shape factor is negative; (3)The ZDR arc of supercell hailstorms is characterized by a large reflectivity factor gradient ZH, a significant differential reflectivity ZDR, and low correlation coefficient CC and specific differential phase KDP. A considerable number of very large to large raindrops were observed at the ground level, originating from a large amount of ice particles above the melting layer, accompanied by a significant number of smaller raindrops. The microphysical processes are primarily dominated by melting and evaporation; (4)Hail is concentrated in the narrow area at the front of the forward downdraft in the supercell hailstorm, with low-level ZH≥60dBZ, ZDR≤0dB, CC≤0.92, KDP＞1.7°/km, and a core with KDP＞3.0°/km below the melting layer. Large hail, small hail, and graupel appeared sequentially, with a high proportion of large and very large raindrop density, the microphysical processes were mainly dominated by melting and shedding; (5)The period of maximum rainfall intensity occurred in the strong echo area of the forward downdraft after concentrated hailfall, where the number density of raindrops of various sizes increased significantly, leading to a marked increase in rainfall intensity. The peak of rainfall intensity occurred during the period when medium-sized raindrops were predominant. The microphysical processes were primarily dominated by melting and shedding, accompanied by coalescence and fragmentation processes caused by strong winds. (6)At the tail of the forward downdraft, as precipitation is about to end, ZH, ZDR, and KDP decrease synchronously, indicating the presence of medium and light raindrops.The role of the particle size sorting mechanism is pronounced and enduring in the particle distribution of hailstorms. Melting and the shedding are important microphysical processes accompanying the hailfall phase. The processes such as evaporation, coalescence, and fragmentation is phased and localized, contributing to the complexity and diversity of the raindrop spectrum.