强雷暴个例云内闪电与上升气流及液水含量关系的三维数值模拟

3D Modeling on Relationships among Intracloud Lightning,Updraft and Liquid Water Content in a Severe Thunderstorm Case

利用建立的三维闪电数值模式,模拟研究了北京2001年8月23日一次强雷暴发展过程中的云内闪电通道特征及其与上升气流和液水含量(LWC)之间的关系。结果发现:在强雷暴发展过程中,由于雪晶往往在上升气流相对较弱及LWC较低的地方形成、发展,与霰粒子之间的非感应起电过程首先发生在这些区域,然后发生电荷分离。因此,云内闪电往往在上升气流较弱和LWC相对较低的区域触发。闪电触发后,上行先导延伸区域的LWC较小,而下行先导延伸区的LWC取决于强风暴云发展的阶段。强风暴成熟期发生的闪电,下行先导可以延伸到较大LWC区,而无法延伸到LWC最大区。强雷暴衰退期发生的闪电,下行先导可以延伸到LWC最大区。

A three-dimensional hail-bin cloud model coupled with electrification process has been developed and used for simulating lightning process in a severe thunderstorm in Beijing City in China. The characteristics of intracloud lightning channel and its relationship with updraft and liquid water content have been analyzed. Results indicate that in the evolution of the thunderstorm, snow particles are often formed where updraft is weaker and liquid water content （LWC） is lower. Snow particles develop there, and gain charges in the non-inductive charging process with graupel there. Therefore, intracloud lightning flash often initiates where updraft is weaker and LWC is less. After initiation, the upward leaders propagate to the area where LWC is less, while LWC where the downward leaders propagate to depends on the evolution stage of the thunderstorm. The upward leaders could propagate to the area where LWC is a little greater but not the maximum in the mature stage of the thunderstorm. However, the downward leaders could propagate to the center areas of LWC during the process of the decay of the thunderstorm.