塔里木盆地西缘两次致灾冰雹环境场和雷达特征对比分析

Comparative Analysis of Environmental Field and Radar Characteristics of Two Hail Disasters in Western Tarim Basin

利用常规气象观测、多普勒雷达及NCEP再分析等资料,对比分析2018年5月19日(简称“5·19”)和7月29日(简称“7·29”)喀什地区北部2次致灾冰雹天气的环境场及雷达特征。结果表明:(1)两次冰雹都是在有利的中亚低涡环流背景下产生,午后垂直温度递减率增大,中高层干冷空气与低层暖湿空气交汇增强了大气不稳定性。较好的对流不稳定条件、风(垂直)切变、适宜的0℃层~-20℃层高度,为冰雹产生提供了有利的环境场条件。另外,两次过程中亚低涡中心强度和南伸的位置不同,“5·19”过程低涡位置偏南;低层触发系统不同,“5·19”为地面中尺度辐合线触发对流,“7·29”为700 hPa切变线附近触发;θ_(se)能量锋区、比湿、中高层干冷空气入侵势力、深层风切变等变化上“7·29”冰雹比“5·19”冰雹偏强;(2)雷达回波形态和风暴类型上,两者均为多单体风暴,反射率因子剖面均出现弱回波区和悬垂回波等特征结构,≥50 dBZ的回波伸展到-20℃层高度以上;径向速度图上均出现中小尺度辐合特征;冰雹发生前VIL值出现跃增,冰雹结束后迅速下降,可以作为监测冰雹特征之一。

Based on the data of meteorological conventional observation,radar and NECP reanalysis data,the environmental field and radar structure characteristics of two hail weather processes in Kashgar on May 19 and July 29,2018 were comparative analyzed.It shows that,First,both events happened under the background of the Central Asian vortex,with vertical temperature decline rate increased in the afternoon.The intersection of the dry and cold air advection in the middle-upper layer,the warm and wet air in the low layer enhanced the atmospheric instability.Favorable hydrometer conditions,vertical wind shear,and the suitable height of-20℃、0℃layer provided advantagous environmental field for the hail occurance.There are some difference between the two processes as well.The intensity of the vortex was stronger during the“5·19”process and the position of vortex was southward.The trigger system of“5·19”was surface mesoscale convergence line,while the“7·29”was triggered by the shear line.Second,the radar echo indicates that,the two hail events were both caused by multiple storm.The reflectivity factor profile shows weak echo region and overhang echo,with the echo of≥50 dBZ extends to the-20℃layer;while the VIL value increased sharply before hail.Such a featured structure were more obvious in the“7·29”process.