Characteristic Analysis Of Continuous Hailfall In The Context Of Cold Vortex In The Beijing-Tianjin-Hebei Region

Cold vortex is cold low pressure closed circulation system, which is present in the middle and high latitudes of the upper troposphere. Because the cold the vortex can often bring severe weather such as snowstorms, thunderstorms, high winds, hail, heavy rain, the meteorologists have attention it a long time. Hail is one of the major severe weather in summer in the North China, and often bring serious harm to people’s lives and property.How to make predictions prior to the occurrence of disasters has important practical significance.In this paper, cold vortex was firstly defined. Using weather map from April to September during2000-2011,the temporal-spatial distribution and life characteristics of cold vortex were studied. Disaster weather data from176stations in Beijing-Tianjin-Hebei region from April to September during2000-2011and NCEP1°×1°reanalysis data were used to analyze the temporal-spatial distribution characteristics of continuous hail of Beijing, Tianjin,Hebei region and the relationship between cold vortex. The results showed that:The number of cold vortex was slightly increased,cold vortex mainly occurred in northeast China to the east of Lake Baikal, and long-lived cold vortex was accounted for70%; Cold vortex was a major weather system. Causing continuous hail in the Beijing-Tianjin-Hebei region,was long-lived cold vortex; Continuous hail in the context of cold vortex had significant diurnal variation; Continuous hail occurred more in mountainous area than on the plains, more in north area more than the south area;Continuous hail could occur in any period of cold vortex, daily average number of hail stations is the most in the context of mature cold vortex, hail Terminus is few in the context of demise cold vortex,but daily average number of stations are greater. and Continuous hail mainly occurred in the southerly position of the cold vortex center; The distance between Continuous hail and cold vortex was about200-1200km.The continuous hail mainly affected by t the cold vortex and rear transverse trough; Continuous hail occurred in different position of moving cold vortex.Through16cases of continuous hailfall in the context of cold vortex in the Beijing-Tianjin-Hebei region and5cases without hail occurred in the context of cold vortex, as well as11continuous hail events in the context of deep cold vortex and5continuous hail events in the context of shallow cold eddy,the second part mainly analyzed the largescale background, physical quantities, the convection parameters of the conditions for the hailfall, and established continuous hail mesoscale conceptual model in the context of the cold vortex in the Beijing-Tianjin-Hebei region. Six hours before a hail occurred, the cold vortex which caused hail configuration of the system was conducive to the occurrence of convection. High and low level Jets passed through the Beijing-Tianjin-Hebei region. Cold vortex with hail in the Beijing-Tianjin-Hebei region had a strong unstable atmospheric stratification, and moisture conditions better than cold vortex without hail. Thermal Index could reflect the difference between hail and non-hailfall type. Deep cold vortex had larger meridional scale than shallow-cold vortex. In the context of shallow cold vortex, blocking higher than deep cold vortex in the northeast region of China, and the North China was controlled by the warm ridge.The cold front is the main trigger of hail in the Beijing-Tianjin-Hebei region in the context of deep cold vortex. Mesoscale convergence line or barometric low usually acted as a trigger of hailfall in the contxt the shallow cold vortex.-20℃layer height, T850-500,0-3km and0-6km vertical wind shear could better reflect differences between the shallow cold vortex and deep cold vortex.Finally, two continuous hail events were analyzed largescale background, dynamic and thermal conditions from May31to March6in2005and June22-28in2008, using NCEP data, radar data, satellite data and ground radiosonde data. These two hail events occurred in the context of high-altitude cold vortex with circulation, but the cold vortex position, mainly affecting the system, and the situation on the ground there were significantly different. For the event from the31May to2Jun in2005,cold vortex moved faster, and for the22-28June in2008, cold vortex was stability and seldomly moved due to the blocking high. From31May to2June in2005dynamic effect was obvios, but22-28June in2008thermal effect was obvious. From31May to2June in2005, TBB was characterized by a typical cold vortex cloud system, and it developed from the spiral cloud band of southeast direction of the cold vortex into the strip cloud system between southwest and northeast. From22to28June in2008,TBB was mainly manifested the speckled cloud system, and the multiple MCS of formation combined development. Radar data had a good relationship with hailfall position. Sounding data has some reference significance, subject to the site and time resolution.However, the three dimensional structure of the mesoscale convective system at the background of cold vortex need further study.