江苏台风龙卷环境条件与雷达关键特征分析

By using the conventional observation, automatic station, Doppler radar and FNL reanalysis data (1°X1°), this paper analyzes the spatial and temporal distribution characteristics, ambient conditions and radar key features of the typhoon-tornadoes in Jiangsu during the 2007 — 2018, and compares with the corresponding characteristics of typhoon-tornadoes in Guangdong. The analysis results indicate that the frequency of typhoon-tornadoes in Jiangsu has increased compared with the past, and the occurrence time of the tornadoes is concentrated in July and August from 16:00 BT to 20:00 BT. Jiangsu typhoon-tornadoes occur after typhoon landfall 24 hours later, different from Guangdong typhoon-tornadoes, which occur within 24 hours after typhoon makes landfall. A strong preference for tornado occurrence is in the northeast quadrant with respect to land-falling typhoon center. High risk areas of tornado occurrence in Jiangsu are concentrated in the central part of Jianghuai and Xuzhou. The low-level jet transports abundant water vapor and unstable energy, providing favorable ambient conditions for tornado, and the ground convergence line is an important system for tornado development. The common ambient conditions for Jiangsu and Guangdong tornadoes appear to be the low, strong deep-layer and low-level vertical wind shear and high storm relative helicity. The major difference between the Jiangsu and Guangdong tornado cases is that the Guangdong tornado has weaker convective available potential energy and convective inhibition and much lower lifting condensation level, but stronger deep-layer and low-level vertical wind shear. About 2/3 of typhoon tornadoes in Jiangsu accompany with tornadic vortex signature (TVS). The thunderstorm cells that produce strong tornadoes are associated with mesocyclone and TVS. Strong tornado is more likely to occur when the lowest level difference velocity of TVS exceeds 23 m • s_1. The lowest level difference velocity of tornado TVS in Jiangsu is weaker, and the maximum shear is smaller (1/3 of that in Guangdong).