2019年6月黄河口6次局地冰雹实例分析

Analysis of 6 local hail cases in the Yellow River Estuary in June 2019

利用常规气象资料、多普勒雷达资料、加密自动气象站资料及第五代欧洲中心再分析资料(ERA5),分析了2019年6月发生在黄河口地区的6次局地冰雹天气过程。结论如下:1)6次降雹过程是在有利的环境条件下产生的,大尺度影响系统是东北(华北)冷涡与横槽、中纬度高空槽;冰雹天气即将发生前,对流层低层多存在逆温,有对流抑制,对流有效位能在1000 J·kg^-1以上,环境比较干,0℃层与-20℃层之间的厚度在1.8~2.3 km,两温度层的高度较经验值偏低。2)雹暴云在发生发展阶段存在最大组合反射率(MaxREF)、回波顶高(ET)和垂直累积液态水含量(VIL)的迅猛跃增;6次雹暴云气柱内冰水含量偏多,且积累迅速,液态水含量较少,雨水含量最少,因而造成降雹时多伴有弱降水。3)雹暴云的中层风场特征表现为雷达径向风的水平切变与垂直切变,而在对流层低层则表现为风向辐合与风速脉动。4)6次冰雹天气发生的地点多在黄河口的沿岸地区;特殊的地理位置有利于在对流层低层形成中尺度风场辐合线,在有利的环流背景下,可激发局地对流或使移入的雷暴云得到迅猛发展,这是导致该地对流频发的原因。

In this paper,6 local hail weather processes in the Yellow River Estuary in June 2019 are analyzed using conventional data,Doppler weather radar products,densified automatic meteorological observation data,and the 5th generation of ECMWF atmospheric reanalyses dataset(ERA5).The results are as follows.1)The 6 hail processes are produced under favorable environmental conditions,and the large-scale synoptic systems are cold vortex and transverse trough in Northeast(North)China and upper-level trough over middle latitudes.When the hail falling process is about to occur,there is temperature inversion in the lower troposphere and convective inhibition.The convective available potential energy is above 1000 J·kg^-1 and the surrounding environment is relatively dry;the thickness between the 0℃layer and the-20℃layer is between 1.8 km and 2.3 km,which is lower than the empirical value.2)There is a rapid increase in maximum composite reflectivity(MaxREF),echo top(ET),and vertically integrated liquid(VIL)during the occurrence and development stage of hail storm.The ice water content is more with rapid accumulation,the liquid water content is less,and the rain water content is the least in the air column of the 6 hail storms,so most of them are accompanied by weak precipitation during hail falling.3)The middle-layer wind field of storm cloud is characterized by horizontal shear and vertical shear of radar radial wind,while in the lower troposphere,it is characterized by wind direction convergence and wind speed fluctuation.4)Most of the 6 hail processes occur in the coastal areas of the Yellow River Estuary,the special topography of which is beneficial to form mesoscale convergence line of wind field in the lower troposphere.Under the favorable circulation background,it is easy to trigger local convection or make the ingoing hail cloud develop rapidly,which is the reason for frequent convection in this area.