孤立单体爆发性增长过程中的宏微观物理特征研究

Macroscopic and Microscopic Physical Characteristics of Isolated Storm Cell during Explosive Growth Process

为探究贵州威宁地区雹暴爆发性增长过程热动力、微物理和闪电活动特征,利用贵州威宁X波段双偏振雷达观测资料对2018-2019年23个降雹个例进行统计分析,对2018年4月25日一次具有“累积带”特征的孤立单体降雹过程的爆发性增长阶段热动力、微物理及雷电活动进行详细分析。结果表明:(1)通过统计,0℃层以上45 dBZ体积增长最大速率出现时间较降雹时间提前5~15 min,与最大上升气流(本文用径向速度垂直分量表征上升气流强度)提前量相关性最大,相关系数达到0.778。(2)在爆发性增长阶段上升气流对低密度霰(LDG)数量增长的贡献最大,上升气流强度与低密度霰最大增长速率相关系数达到0.62。(3)孤立单体雹暴爆发性增长阶段单体内上升气流强度大,正径向速度垂直分量最大值维持在2 m/s以上。(4)爆发性增长前期强上升气流将大量水汽输送至-10℃高度以上形成大量冰晶和低密度霰,同时0℃~-20℃高度范围内过冷水大量堆积形成“累积带”,过冷水粒子增长速率最高达到每分钟17.8距离库数。(5)爆发性增长后期雨夹雹大量生成,其主要贡献源为高密度霰在“累积带”区域过冷水条件下进行转化,高密度霰粒子库数占比减少1.94个百分点。(6)爆发性增长阶段雹云内冰晶和霰的数量急剧增多、动力场剧烈变化,非感应起电率增加,闪电频数显著增加。这些指标反映出贵州威宁孤立单体雹暴及其内部“累积带”在爆发性增长阶段的特征变化,为监测孤立单体雹暴爆发性增长以及冰雹预警提供一定参考依据。

In order to explore the characteristics of thermal dynamics,microphysics and lightning activity in the process of hailstorm explosive growth in Weining,Guizhou,the observation data of X-band dual-polarization radar in Weining,Guizhou were firstly used for statistical analysis of 23 hailstorm cases from 2018 to 2019.Then,the thermal dynamics,microphysics and lightning activity in the explosive growth stage of an isolated monomer hail process with the characteristic of"accumulation zone"on April 25,2018 were analyzed in detail.The results show that:(1)according to statistics,the occurrence time of the maximum volume growth rate of 45 dBZ above 0℃-layer is 5~15 min compared with that of hail falling time,and it has the greatest correlation with the advance amount of the maximum updraft(the vertical component of radial velocity was used to represent the strength of updraft in this paper),with the correlation coefficient reaching 0.778.(2)In the stage of explosive growth,updraft makes the largest contribution to the quantity growth of lowdensity graupel(LDG),and the correlation coefficient between updraft intensity and maximum growth rate of low-density graupel reaches 0.62.(3)In the stage of hailstorm explosive growth,the updraft intensity in the single cell is large,and the maximum value of the vertical component of the positive radial velocity remains above 2 m/s.(4)In the early stage of explosive growth,a large amount of water vapor is transported by strong updraft above the height of-10℃-layer to form a large number of ice crystals and low-density graupel.At the same time,a large amount of supercooled water accumulates in the height range of 0℃~-20℃to form a"accumulation zone".The growth rate of supercooled water particles reaches the maximum of 17.8 pools per min.(5)In the later stage of explosive growth,rain and hail are generated in large quantities.Its main contribution source is conversion of high-density graupel under super-cold water conditions in the"accumulation zone"area,and the number of high-density graupel particle reservoir decreases by 1.94%.(6)In the stage of explosive growth,the number of ice crystals and graupel in hail cloud increases sharply,the dynamic field changes dramatically,the non-inductive electrification rate increases,and the lightning frequency increases significantly.Consequently,these indexes reflect the characteristic changes of isolated hail storm and its inner"accumulation zone"in the stage of explosive growth in Weining,Guizhou,and provide a certain reference for monitoring the explosive growth of isolated monomer hail storm and hail early warning.