Staged characteristics analysis of a severe convection over the Dongting Lake area based on dual-polarization Doppler weather radar data

The multi-cell storm stage and squall line stage of a severe convective weather process over the Dongting Lake on 15 May 2021 in this study are analyzed mainly based on S-band dual-polarized doppler weather radar data. The study focuses on the analysis of the supercell storm I2 in the multi-cell storm stage. The results are as follows. (1) During the initial period of the I2, the strong echo area (the horizontal reflectivity factor, Z_H > 55 dBz) and the differential reflectivity factor (Z_DR) column (Z_DR > 2.5 dB) extend to Wet Blub Zero (WBZ) level, corresponding to the areas with large specific differential phase (K_DP) (> 1.7 °·km^-1) and large correlation coefficient (CC) (0.9-0.99). It indicates that during this period, the precipitation phase is dominated by water condensate mingled with large raindrops, and these supercooled raindrops provide hail embryos for the later hail development. (2) During the hail colliding-growth period of the I2, Z_H intensity and height increase rapidly, and vertically integrated liquid water content (VIL) shows an obvious leap increase. The strong-echo center (Z_H > 60 dBz) extends to the level of above -10 ℃. In the corresponding regions, the Z_DR drops below 0, the Z_DR column (Z_DR> 2.5 dB) extends to the level of -10 ℃, CC drops, and a "hole" appears in the K_DP value area. These indicate that the precipitation during this period is dominated by solid particles and these solid particles are in an increasing period. (3) During the mature hailfall period of the I2, the bottom of the Z_H intensity center (Z_H > 60 dBz) drops below the WBZ level and the CC is locally as low as 0.8. There are Z_DR negative areas and K_DP voids in the corresponding area. These means that the dragging effect of the falling hail further weakens the strength of the updraft, which means that the hail is about to land. Then comes the squall line stage. (4) Unlike the multi-cell storm stage, the squall line stage has anomalously large K_DP values and Z_DR values greater than 1. (5) Before the occurrence of extreme gales of the squall line stage, the areas with strong echo greater than 55 dBz and velocity larger than 27 m·s^-1 extend below 1 km, and the K_DP in the strong echo area is obviously large, corresponding to the strong downdraft. Besides, the strong precipitation dragging effect caused by the melting of descending precipitation particles intensifies the generation of extreme gales.