Comparative Analysis of Low-Level Dual Polarization Parameters of Different Types of Severe Rainfall Storm
Based on the Shandong S-band dual polarization Doppler weather radar data, sounding data and surface precipitation observation as well as the environmental background features, severe rainstorms are divided into the thunderstorm gale (accompanied by severe precipitation or hail) dominated type (referred to as “mixed type”) and the simple severe precipitation dominated type (referred to as “precipitation dominated type”). Three types of minute precipitation magnitudes are considered for each type of rainstorm, and comparative analysis of the low-level dual polarization parameter characteristics of severe rainstorms in the six different scenarios is conducted in this paper. The results show that as the magnitude of minute precipitation increases, the low-level reflectivity factor (ZH) and specific differential phase (KDP) of both types of severe rainstorms increase. The differential reflectivity (ZDR) and correlation coefflicient (CC) of “precipitation dominated type” rainstorms do not show significant changes, while the ZDR and CC of “mixed type” storms decrease. This indicates that with the increase in magnitude of precipitation, the number of large-size hails in the lower layers of “mixed type” severe rainstorms increases, resulting in the decrease in ZDR and CC. For high-intensity precipitation above 2 mm·min-1， the low-level ZH, ZDR, and KDP of “mixed type” rainstorm are concentrated at 50.5-57.0 dBz, 1.7-2.7 dB, 2.4-4.3°·km-1, and CC is above 0.960， while the low-level ZH, ZDR, and KDP of the “precipitation dominated type” rainstorm are concentrated at 49.5-53.5 dBz，〖JP〗 1.2-2.1 dB, 2.5-3.9°·km-1 with CC above 0.970. This means that most “mixed type” rainstorms contain a large amount of small-size hails around 5-10 mm during high-intensity precipitation. These smaller hailstones tend to melt into larger rain droplets in the lower layers, increasing the ZDR value and also making the echo intensity ZH higher than that of the “precipitation dominated type”. At the same minute precipitation level, the low-level ZH and ZDR of the “mixed type” rainstorm are greater than those of the “precipitation dominated type” storm, and CC is smaller than that of the “precipitation dominated type” storm. This is because the former owns not only more 5-10 mm smaller hailstone but also some large hail particles. The larger KDP in the lower layer of rainstorms has obvious indicative significance for the two types of severe precipitation.