浙江地区一次飑线大风的观测与机理分析OA

This study analyzes a squall line event that occurred in northern Zhejiang Province on June 24,2022,using ERA5(the fifth generation ECMWF Re-analysis,ERA5)reanalysis fields from the European Centre for Medium-range Weather Forecasts(ECMWF),surface meteorological observations,sounding data,dual-polarization radar data and analysis results from the Variational Doppler Radar Analysis System(VDRAS).The synoptic background of this squall line event included:an upper-tropospheric jet divergence zone existed in the upper troposphere,a mid-level trough guiding cold air southward,and a low-level jet provided sufficient moisture supply.Additionally,a large Convective Available Potential Energy(CAPE)increased convective potential,while a dry layer in the mid-troposphere contributed to the favorable environment for the occurrence of the wind event.Dual-polarization radar observations revealed the convection system manifested as a merging bow echo,where the squall line merged with forward convective cell and subsequently form the bow-shaped structure.The bow echo exhibited reflectivity values exceeding 55 dBZ,with a distinct weak echo region in the rear.The VDRAS wind field indicated that there was a high-value area of horizontal wind speed behind the intense radar echoes.As the system developed and matured,the rear inflow jet strengthened and descended,leading to surface wind acceleration.Quantification of the factors contributing to the downward motion through the vertical momentum equation revealed that the downdraft was primarily dominated by the buoyancy term.Dry intrusion caused the temperature and humidity of the lower-level air mass to decrease,generating negative buoyancy,which enhanced the downward momentum transfer of the rear inflow jet and ultimately increased the intensity of the surface outflow.The synergy between the rear inflow jet and the dry intrusion was identified as the key mechanism for the strong surface winds.