Abstract:Investigating the evolution of the polarimetric signatures, dynamical and microphysical characteristics in the heavy hail supercell are beneficial to understanding the physical processes that lead to heavy hail formation, determining possible precursive signatures associated with heavy hail formation and growth, and improving warnings for heavy hail supercell. A supercell accompanied by heavy hail in southern Fujian on 22 April 2019 which was detected by the Xiamen S-band dual-polarization radar was analyzed using the dual-Doppler radars wind field retrieval and hydrometeor classification algorithm. The study reveals that the differential reflectivity (Zdr) at the beginning portion of the three-body scatter signature (TBSS) was very high, located radially behind the horizontal reflectivity (Zh) core. It was also found that the cross-correlation coefficient (CC) is very low in the TBSS. Polarimetric signatures associated with TBSS are good indicators of heavy hail aloft. The polarimetric signatures of the heavy hail region manifested as high values of Zh collocated with near-zero value of Zdr. However, during the heavy hail descent, Zdr increased and CC decreased on the periphery of the hail core. The increased Zdr and decreased CC due to the increasing presence of water coating on the melting hailstones. At low level, an area of enhanced specific differential phase (Kdp) was observed within the Zh core of supercell, which was called the Kdp foot. Kdp was less sensitive to heavy hail and thus was a better indicator of melting hail. Therefore, the Kdp foot may be a favorable index of the downdraft zone which was driven by melting of hail. The horizontal wind field showed a distinct double vortex developing in the supercell. The double vortex structure contributed to the development of supercell and the circulation growth of heavy hail. On the northeast of the mesocyclone, a zone of modest Zh, low Zdr, and high CC were observed, called the graupel belt. The hydrometeor classification algorithm suggests that graupel is the dominant hydrometeor type. Because of the proximity to the mesocyclone, some of the graupel were entrained into the updraft, serving as hail embryos. The schematic diagrams of polarimetric signatures and three-dimensional wind field structure of the heavy hail supercell are given based on these analyses.