湖南衡阳“4.04”强下击暴流预警关键点及环境条件分析

Analysis of key warning points and environmental conditions for the‘4.04’strong downburst event in Hengyang of Hunan

2023年4月4日下午湖南衡阳出现一次强下击暴流过程(简称“4.04”强下击暴流),造成严重灾害。利用常规气象观测、多普勒天气雷达、NCEP1°×1°再分析等资料对该过程极端大风的预警关键点与环境条件进行分析。结果表明:(1)“4.04”强下击暴流发生在“斜压锋生类”天气系统配置下,地面冷锋提供了触发条件。探空曲线上干下湿特征明显、大气对流参数及订正后的对流有效位能表现出明显的不稳定特征,垂直风切变强,利于极端大风发生。(2)中尺度对流系统(MCSs)弓状回波扫过衡阳,造成区域性下击暴流;极端大风发生在对应风暴单体快速移动时,最大反射率因子达60 dBz,垂直积分液态水含量及质心高度快速下降;反射率因子具有明显倾斜结构,弓状回波、后侧入流急流、径向速度模糊特征明显;低仰角“非对称速度大值区”和“速度对纯辐散”是极端大风预警关键点。(3)强下击暴流发生在斜压锋生类天气系统配置下,地面冷锋提供了触发条件。探空曲线上干下湿特征明显、大气对流参数及订正后的对流有效位能表现出明显的不稳定特征,垂直风切变强,利于极端大风发生。(4)强下击暴流对流潜势明显,低层水汽通量辐合强、比湿大;具备一定的热力不稳定及垂直上升运动条件,且有低层辐合、高层辐散与之配合;冷空气对本次过程发生发展起到了重要作用。

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.