Statistical Analysis of Continuous Hailfall Under the Background of Cold Vortex in the Beijing-Tianjin-Hebei Region

Cold vortex is firstly defined.Using synoptic chart from April to September during 2000—2011,the sptio-temporal distribution and life characteristics of cold vortex are studied.Besides,disaster weather data from 176 stations in Beijing-Tianjin-Hebei region from April to September during 2000—2011 and NCEP 1°×1° reanalysis data are used to analyze the sptio-temporal distribution characteristics of continuous hailfall of Beijing,Tianjin,Hebei Region and its relations with cold vortex.The results show that the number of cold vortexes is increasing,which mainly occur from Northeast China to the east of Lake Baikal,and long-lived cold vortexes account for 70%.It is the long-lived vortex that causes the continuous haifall in the Beijing-Tianjin-Hebei Region and the continuous hail in the context of cold vortex exhibits significant diurnal variation,appearing more in mountains than on plains,more in the north than in the south.Continuous hail mainly occurs in the south of vortex center,and can occur in any stages of cold vortex.The distance between continuous hail and cold vortex is about 200—1200 km.The continuous hailfalls are mainly affected by the cold vortex and its rear transverse trough,and occur in different position corresponding to cold vortex with different speeds.