Analysis on radar echo and airflow fields of a splitting hail-producing supercell ahead of a squall line

An obvious supercell splitting process occurred in southern Zhejiang province on 23 April 2019. To study the splitting characteristics of the supercell storm, the splitting process is analyzed using multiple-group dual-radar three-dimensional wind field retrieval networking technology and the products of radar, wind profile radar and radiosonde data. The supercell storm occurred in an environment of moderate vertical wind shear (more than 15 m/s between the surface and 500 hPa). It formed in front of the bow echo of the squall line, and its obvious three-body scattering signature (TBSS) lasted for a long time. The splitting started from the middle layer on the north side of the original storm, and then extended rapidly both upward and downward. The leftward-moving supercell had an obvious mesoscale anticyclone vortex structure. It showed a typical supercell structure composed of suspension, strong echo column and strong updraft, forming an approximate mirror symmetrical state to the rightward-moving supercell in terms of morphology and airflow structure. When the two storms almost separated, hails fell in both storms, corresponding to strong downdrafts. In the developing stage of the new splitting storm, the maximum vertical velocity and maximum negative divergence in their vertical profiles were increasing, while the two physical quantities of the original storm in the corresponding period were decreasing. The vorticity of the two storms gradually increased simultaneously during the whole splitting process, and the rotation degree of the cyclonic and anticyclonic vortexes increased with the same trend. The vertical wind shear vectors in the lower layer rotated counterclockwise with increasing height, the leftward-moving anticyclonic supercell strengthened and developed, and the rightward-moving cyclonic supercell was suppressed. This is consistent with the theoretical research results. The airflow characteristics of this case retrieved from radar observations are consistent with the radial velocity products, and the retrieved wind field is basically reliable, which provides a further reference for intuitively understanding the dynamic characteristics of supercell storm splitting.