Comparative Analysis on Dual Polarization Features of Two Severe Hail Supercells

Abstract

Using S-band dual-polarization weather radar data, sounding and ground meteorological observations, and disaster investigation reports, the similarity and difference of dual polarization parameters between Lixian and Zhangqiu supercells with hails above 50 mm are analyzed. Lixian supercell occurred at Lixian, Heibei Province on 25 June 2020, and Zhangqiu supercell occurred at Zhangqiu, Shandong Province on 9 July 2021. The results show that two supercells occurred in similar weather pattern (northwest flow) and large vertical wind shear environmental conditions which is conducive to the generation and maintenance of supercell storms, but Zhangqiu supercell is with stronger convective effective potential energy, larger humidity, and higher wet bulb 0℃ layer height. The main similarities include obvious differential reflectivity (ZDR) arcs along the forward flank of supercell storms, ZDR rings distributed around the updraft in the middle layer, and obvious ZDR columns and specific differential phase (KDP) columns above the 0℃ level. ZDR arcs are associated with large raindrops or small melting hail particles, ZDR columns mark the location of convective updrafts as large raindrops or wet ice particles are lofted to subfreezing temperatures, and KDP columns are dominated by large concentrations of small and medium-sized raindrops or melting ice particles. The similarity of the updraft structure plays a key role in the commonness or similarity of the polarization characteristics. The main differences are stronger reflectivity factor ZH, but lower height of ZDR column and KDP column in Lixian supercell. The strong overhang echo above the weak echo area in Lixian supercell contains large hail particles generated by cumulated growth. After the overhanging large hail particles enters the descending channel, they will produce obvious growth again and become more irregular, resulting in stronger horizontal polarization reflectivity factor ZH and smaller correlation coefficient. The obvious differential attenuation signature and nonuniform beam filling are observed in low level of Lixian supercell. The differential attenuation caused a decrease in the differential reflectivity as the beam propagates through large hail cores. Nonuniform beam filling is generated by inhomogeneous filling of different hydrometeor particles in the sampling volume. Under similar weather patterns, the distribution characteristic of humidity vertical profile is one of the key environmental factors of storm intensity. Lixian supercell storm occured in very low humidity vertical distribution environment, while Zhangqiu supercell storm occured in wetter environment.

Keywords

• supercell
• dual-polarization
• difference