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

There are usually intensive electrification and active discharges in severe hail storms because of strong updraft and complex microphysical processes with partic ipation of ice particles. Although a lot of researchers have analyzed the lightn ing 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 th e warning of severe convective weather, we studied the cloud to ground(CG) lig ht ning activities in one severe convective weather occurred in Shandong Province, caused by Northeast cold eddy situation on 1 June 2002. CG flashes occurred in t he weather event were observed by Shandong Lightning Detection Network (SLDN), which consists of 10 sensors covering all over the Shandong Province. The tempora land spatial distribution of CG lightning is investigated for the three hailsto rms 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 flashe s mainly occurred in the region with a cloud top brightness temperature lower th an -50 ℃. Negative CG flashes usually clustered in the lower temperature re gion and tended to occur in the region with maximum temperature gradient, while the p ositive 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, a nd the peak positive flash rate was a little prior to the hail events. The thund erstorm could lead to disastrous weather when positive CG lightning activities o ccurs in cluster. Severe thunderstorms sometimes present a low flash rate at its vigorous stage, which are probably caused by the 'mechanism of charge region li ft' through investigating the reflectivity involution. Combined with the total l ightning (intracloud and CG) data obtained by LIS on TRMM, the phenomenon of hig h ratio of intracloud to CG flash in severe hailstorm has been discussed. The co mpetition of same charge resources between different lightning types can also be helpful to explaining the cause of low CG lightning activities in severe storms .