包含三次降雹的雹暴过程地闪活动特征分析

Characteristic analysis of cloud-to-ground lightning activity during hailstorm process with three hail falling events

为研究雹暴的地闪活动特征,利用地闪资料与3组双雷达探测资料反演的风场,对包含3次降雹的一次雹暴过程的地闪活动特征及其与雹暴动力、微物理条件的关系进行了分析与讨论.主要结果为:(1)整个雹暴过程中发生了3次持续降雹事件,并伴随着3次地闪活动出现峰值,在降雹前地闪频次均有跃增现象.降雹开始后,地闪频次均迅速减少.(2)整个雹暴过程中对应地闪接地位置的0℃层、-20℃层高度的垂直速度范围分别集中在-2-2 m/s和-10-10 m/s.但3次降雹时段的地闪接地位置分别对应-20℃层高度的强下沉气流区附近、强上升与下沉气流区的交界区和弱的下沉气流区.(3)选取的雹暴内最大反射率(Zmax)、-20℃层高度最大反射率(Zmax_-20℃)、-20℃层高度大于40 dBz格点数(Sum(Z-20℃>40 dBz))3个雷达回波参量与地闪频次变化趋势一致,其相关系数分别为0.64、0.64、0.76.选取的对应地闪接地位置-20℃层高度的最大垂直速度绝对值(|W|max-20℃)和-20℃层高度以上垂直速度绝对值大于5 m/s的体积(|V|5 m/s↑-20℃)两个垂直速度参量与地闪频次成正比,且阶段最大值与地闪频次阶段最大值对应,相关系数分别为0.72、0.65.综合考虑动力和微物理影响的可降冰质量通量(F)与地闪频次的相关最显著,相关系数达0.85.整个雹暴过程发展最旺盛的第2次降雹阶段的地闪频次较低,推测强动力过程作用下的电荷结构特征不利于地闪发生.但动力过程在整个雹暴过程中具有正向支配作用,上升气流变化超前于冰晶质量和闪电频次变化,影响着雷达回波变化.

The characteristics of cloud-to-ground(CG)lightning activity of hailstorms are an important issue.Based on the CG lightning data and wind fields retrieved by three groups of dual-Doppler radar,the characteristics of CG lightning activity in a hailstorm process that included three hail events and their relationship with hailstorm dynamics and microphysical conditions are analyzed and discussed.The results reveal that:(1)Three consecutive hail events occurred during the whole hailstorm process,accompanied with three peaks of CG lightning activity,and the CG lightning flash rate increased rapidly prior to hail falling.After the hail began,the CG lightning flash rate decreased rapidly;(2)During the whole hailstorm process,the vertical velocity at 0℃ and−20℃ levels corresponding to CG lightning position were concentrated within the ranges−2-2 m/s and−10-10 m/s,respectively.However,the CG lightning positions during the three hail periods respectively corresponded to the strong subsidence airflow zone nearby,the boundary area between strong rising and sinking airflow zone and weak subsidence airflow zone at−20℃ level;(3)The three radar echo parameters,i.e.,the maximum reflectivity of the hailstorm Zmax,the maximum reflectivity at−20℃ level Zmax_−20℃ ,the grid numbers of greater than 40 dBz at−20℃ level Sum(Z􀀀20℃ >40 dBz),had the same trend as the CG lightning flash rate,and their correlation coefficients are 0.64,0.64 and 0.76,respectively.The two vertical velocity parameters,i.e.,the absolute value of maximum vertical velocity at−20℃ level corresponding to CG lightning position|W|max−20℃ and the volume number of the vertical velocity absolute value greater than 5m/s above−20℃ level|V|5 m/s↑−20℃ ,are proportional to the CG lightning flash rate and their correlation coefficients are 0.72 and 0.65 respectively.The maximum values of parameters of the stage corresponded to the CG lightning flash rate maximum value of the stage.Considering the dynamic and microphysical effects,the precipitation ice mass flux F has the most significant correlation with the CG lightning flash rate,and their correlation coefficient is 0.85.The CG lightning flash rate was low in the second hail stage,when the hailstorm developed most rigorously.It is inferred that the characteristics of charge structure under strong dynamic process is not conducive to the occurrence of the CG lightning.However,the dynamic process played a positive dominant role during the whole hailstorm process.The updraft changed ahead of the ice crystal mass and lightning rate changes,and affected the radar echo changes.