Analysis of key warning points and environmental conditions for the'4.04'strong downburst event in Hengyang of Hunan
On the afternoon of April 4,2023,an intense downburst event(referred to as the'4.04'strong downburst event)occurred in Heng-yang of Hunan,causing serious disasters.In this study,an analysis is conducted to examine the key warning indicators and environmental conditions for extreme strong winds by using conventional meteorological observations,Doppler weather radar data,and NCEP 1°×1°reanaly-sis data.The results are as follows.(1)The'4.04'strong downburst event takes place under a'baroclinic frontogenesis'weather system,with a surface cold front as the triggering mechanism.The Skew-T plots display the clear characteristics of high-level dry and low-level moisture,unstable atmospheric convective parameters,and unstable corrected convective available potential energy(CAPE),along with strong vertical wind shear.These factors facilitate the occurrence of extreme strong winds.(2)A mesoscale convective system(MCS)with bow echoes sweeps through Hengyang,causing regional downburst events.Extreme strong winds occur when the corresponding storm cells move rapidly.At that time,the maximum reflectivity factors reach 60 dBz,and the vertical liquid water content and centroid height decrease rapid-ly.The reflectivity factors exhibit a noticeable tilted structure,with clear features of the bow echoes,rear-inflow jet,and radial velocity ambi-guity.The asymmetric high-speed regions and velocity convergence at low elevations play crucial roles in extreme wind warnings.(3)The strong downburst event takes place under a'baroclinic frontogenesis'weather system,with a surface cold front as the triggering mechanism.The Skew-T plots display the clear characteristics of high-level dry and low-level moisture,unstable atmospheric convective parameters and unstable corrected convective available potential energy(CAPE),along with strong vertical wind shear.These factors facilitate the occur-rence of extreme strong winds.(4)The strong downburst event exhibited a clear convective potential,marked by strong low-level moisture convergence and high specific humidity.There are certain conditions of thermal instability and vertical upward motion,coupled with low-lev-el convergence and upper-level divergence.Cold air plays an important role in the occurrence and development of downburst.
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