Analysis of a Squall Line Evolution and Impact Factors of Extreme Strong Winds During the Meiyu Period in Zhejiang Province

QIAN Zhuolei; YAN Peiwen; SHEN Xiaolin; SHEN Zhewen; LUO Ling

doi:10.16032/j.issn.1004-4965.2025.027

Abstract：This study analyzes the evolution characteristics of a squall line and the impact factors of extreme strong winds that occurred during the Meiyu period in Zhejiang on 24 June,2022.It utilizes data from multiple sources,including ERA5 reanalysis data,multi-band radar,lightning location data,and wind profile radar data.The results show that the initial convective cells moved into Zhejiang,forming linear convections which subsequently intensified and merged into a squall line.The squall line rapidly progressed to the mature stage due to factors such as backward propagation and the superposition of the outflow boundary with the environmental convergence center.Cloud flashes,which accounted for the highest proportion within the squall line,were mainly observed between 1.5-8 km in altitude during the mature stage of the squall line.Strong winds occurred mainly in areas of high cloud flash frequency.Prior to the occurrence of strong winds,the core of horizontal polarization radar reflectivity(ZH),differential reflectivity(ZDR),and specific propagation phase shift(KDP)columns developed upwards.The extreme strong winds occurred when the centroids of ZH and ZDR rapidly descended.The extreme strong winds of the squall line developed under the persistent influence of the northeast cold vortex during the Meiyu period.The intrusion of dry,cold air in the middle troposphere,along with high energy and high humidity in the low troposphere provided favorable environmental conditions.Moreover,downward momentum transfer,cold pool density currents,and the orographic"funnel effect"also contributed to the intensification of near-surface winds.