Analysis on Causes of a Thunderstorm Gale in the Rear of High-Level Cold Vortex in Northern Zhejiang Province
The causes for the formation of the regional thunderstorm gale in northern Zhejiang Prov-ince on April 12,2020 is analyzed based on the regional automatic weather station data,NCEP/FNL re-analysis data and Doppler weather radar products.The results show that:(1)This thunderstorm gale process was of the high-level cold advection forcing type.The strong high-low level temperature differential advection provided favorable thermal conditions for the thunderstorm gale,and the strong vertical wind shear was beneficial to the maintenance and development of convective storms.(2)The two β meso-scale convective storms were respectively bow-shaped and ribbon-shaped echoes on the PPI image of radar echo.The strong mid-level radial convergence feature on the radial velocity image,the large velocity range above 20 m·s-1 below 1 km altitude,and the high wind speed core descending on the VWP product can all be used as reference indices for nowcasting thunderstorm and strong wind approaching warnings.(3)The surface cold pool and convergence line were formed by precipitation drag and evaporative cooling,and the convergence line was conducive to the maintenance and development of the convective cloud clus-ter.The inflow jet in the back of the convective cloud cluster strengthened the 1 h positive pressure,and,meanwhile,gradually drove the surface convergence line away from the echo main body.The sur-face strong winds were formed by the combined action of cold pool density flow and pressure gradient,and the gale above Scale 8 was mainly distributed in front of the surface cold pool movement and near the 1 h positive pressure center.
thunderstorm galehigh-level cold vortextemperature differential advectionmid-lev-el radial convergencecold pool
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