The Evolution of Hail Cloud System and Character of Its Cloud to Ground Lightning

There was a severe hail storm under the influence of mesoscale convective system in Weifang district,Shandong Province on April 23,1998.Based on the data obtained by the lightning location system,radar and satellite,the variation character of lightning in various periods of hail cloud forming and developing was studied.The results show that the number of lightning per five minutes is less than 20,and the positive lightning frequency is obviously smaller than the negative one in the periods of hail cloud forming and weakening.The lightning average value per five minutes is bigger than 20,and the positive lightning frequency is equivalent to the negative one in the mature stage.The positive one is temporarily bigger than the negative one just before the severe hail beginning.It is also found that the sudden increase of lightning frequency emerged in the 20—30 minutes before the hail fall beginning,while increasing rate is directly related to the intensity of hail storm.The moment of hail beginning is consistent to that of the maximum value of lightning emerging.

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