Physical Index Analysis of Summer Night Thunderstorms in Lhasa Area

Zhao Dingchi; Li Yi; You Wei; Hei Fei; Zhong Junjie; Hou Yongqiang

doi:10.16765/j.cnki.1673-7148.2017.01.016

Abstract：The large scale thermal and dynamic effects of Qinghai Tibet plateau result in the unstable air and frequent summer thunderstorm activities in plateau area.The area of Qinghai Tibet plateau becomes the most thunderstorms area in the same latitude zone in the northern hemisphere.Using the surface observational and radiosonde data from 2004-2009,this paper analyzed temporal distribution and background characteristics of summer night thunderstorms in Lhasa area.The results showed as follows.1)Thunderstorms in Lhasa area mainly occurred during 14:00-23:00,while the period of 17:00-20:00 had the most numbers with more than 60％ of the total thunderstorms.2)In terms of the characteristics of the whole layer atmosphere,when the thunderstorms occurred during 20:00-02:00,the layer's humidity ratio and pseudo-equivalent temperature (θse) at 20:00 was higher than that without thunderstorms,especially at 400 hPa layer.But there was no obvious temperature difference between them.The indicative functions of some indexes to thunderstorm were also analyzed,including the lifting condensation level (LCL),θse in the 400 hPa layer,modified KI,SI indexes and average vertical wind shear index(MS)between 300 hPa to 400 hPa.The analysis results showed as follows.1) Each index could well distin guish the thunderstorm days and non-thunderstorm days.2) TSS score of each forecast index from high to low was followings:θse ＞ 352.1 K in the 400 hPa layer,with 0.401 TSS score;the modified KI ＞ 15.7 ℃,TSS score was 0.373;the modified SI ＜ 3.20 ℃,TSS score was 0.288;LCL ＞ 441.4 hPa,TSS score was 0.276;MS ＜ 1.87 m · s-1 · km-1,TSS score of 0.201.θse in the 400 hPa layer and modified KI index had better indication to night thunderstorm in Lhasa area.Stability parameters had better indicative significance than wind shear parameters to night thunderstorm.