一次冷涡天气系统中雹暴过程的地闪特征分析

A CASE STUDY OF CLOUD-TO-GROUND LIGHTNING ACTIVITIES IN HAILSTORMS UNDER COLD EDDY SYNOPTIC SITUATION

利用地面雷电定位系统、多普勒雷达和卫星观测资料,对2002年6月1日山东地区冷涡天气系统下的3个雹暴过程的地闪特征进行了详细分析,结果表明,在同样的天气条件下,产生冰雹的3个强雷暴在不同的发展阶段表现出明显不同的地闪分布特征。通过云图和地闪资料的综合分析发现,地闪主要出现在云顶亮温低于-50℃的云区内,其中负地闪分布比较集中,且偏向云顶亮温水平梯度大的一边,而正地闪则分布比较分散。地闪主要发生在大于40 dBz的区域内,负地闪通常簇集在强回波区(大于50 dBz)或邻近区域,有时密集的正地闪也出现在强回波区或临近区域,但稀疏的正地闪通常发生在强回波外围10-30 dBz的范围内,属于稳定性降水区。结合地面降雹观测资料发现降雹发生在正地闪比较活跃的阶段,正地闪频数峰值略微超前降雹时刻。比较密集的正地闪发生,通常预示着强对流天气(如冰雹、大风等)的发生。强雷暴在发展旺盛阶段通常表现的低地闪频数,可能是由“电荷抬升机制”造成的。

There are usually intensive electrification and active discharges in severe hailstorms because of strong updraft and complex microphysical processes with participation of ice particles. Although a lot of researchers have analyzed the lightning activities in hailstorms and many useful results have been achieved, the evolution of lightning activities and its relations with hail-falling in hailstorms are not quite clear up to now. In order to help the understanding of lightning characteristics in hailstorms and the application of lightning information to the warning of severe convective weather, we studied the cloud-toround（CG） lightning activities in one severe convective weather occurred in Shandong Province, caused by Northeast cold eddy situation on 1 June 2002. CG flashes occurred in the weather event were observed by Shandong Lightning Detection Network （SLDN）, which consists of 10.sensors covering all over the Shandong Province. The temporal and spatial distribution of CG lightning is investigated for the three hailstorms under a same synoptic situation by using the data from SLDN, Doppler radar and satellite. The results show that different thunderstorms presented different lightning features even if under the same synoptic situation. The percentage of positive CG lightning was very high during the period of hail falling. CG flashes mainly occurred in the region with a cloud top brightness temperature lower than - 50 ℃. Negative CG flashes usually clustered in the lower temperature region and tended to occur in the region with maximum temperature gradient, while the positive ones usually spread discretely. Negative CG flashes usually occurred in intense echo regions with reflectivity greater than 50 dBz, while the positive CG flashes often occurred in weak and stable echo regions（10- 30 dBz） or cloud anvils, although they can be observed in strong convective regions sometimes. Almost all hail falling events took place in the stage with active positive flashes, and the peak positive flash rate was a little prior to the hail events. The thunderstorm could lead to disastrous weather when positive CG lightning activities occurs in cluster. Severe thunderstorms sometimes present a low flash rate at its vigorous stage, which are probably caused by the ＇mechanism of charge region lift＇ through investigating the reflectivity involution. Combined with the total lightning （intracloud and CG） data obtained by LIS on TRMM, the phenomenon of high ratio of intracloud to CG flash in severe hailstorm has been discussed. The competition of same charge resources between different lightning types can also be helpful to explaining the cause of low CG lightning activities in severe storms.