云南切变线类短时强降水MCS特征分析

MCS Characteristics of short-term heavy precipitation of shear lines in Yunnan

利用云南省125个国家级自动气象站及3042个区域站降水数据、FY-2E/G云图数据以及探空观测数据,统计2015—2019年由切变线系统影响的云南短时强降水过程,对短时强降水时空分布、中尺度对流系统(Mesoscale Convective System,MCS)系统特征、MCS系统发生发展的环境特征以及对流云系演变特征进行分析.结果表明,云南切变线类短时强降水频次有4个大值中心,分别是云南南部边缘地区、曲靖南部至文山北部、华坪、德宏西部,傍晚至凌晨是强降水发生的主要时段;云南切变线类短时强降水对流云系分成新生对流云团、M_(α)CS和M_(β)CS和带状MCS共4类,75%的切变线类短时强降水是由M_(α)CS和M_(β)CS系统造成,M_(α)CS和M_(β)CS系统中低于–32℃冷云区呈椭圆形,平均面积分别为1.8万km^(2)、10.4万km^(2),存在1个或2个中心,中心云顶亮温低于–52℃.M_(α)CS持续平均时间为3.3 h,其中最长时间为6 h;M_(β)CS持续平均时间为2.3 h,其中最长时间是5 h.短时强降水位于M_(α)CS和M_(β)CS强中心附近或者发展方向梯度大值区.综合分析了高低空系统配置的结合、对流发生的条件、MCS的发生及消退和降水特征,旨在建立由切变线引起的4种短时强降水过程的概念模型,从而为云南省短时强降水的预测提供关键技术支持.

The short-time heavy precipitation processes over Yunnan Province caused by the shear lines during 2015–2019 are obtained,based on the precipitation data from the 125 national automatic weather stations and 3042 regional automatic weather stations over Yunnan Province,the FY-2E/G satellite imagery data,and the radiosonde observation.Furthermore,the following four aspects are explored:the characteristics of the temporal and spatial distributions of the short-time heavy precipitation processes,the mesoscale convective systems(MCS),the backgrounds for the occurrence and development of MCS,and the evolution of the convective clouds.The results show that there are four centers for the frequency of the short-time heavy precipitation caused by the shear lines over Yunnan Province,which are the southern edge of Yunnan Province,the regions from southern Qujing to northern Wenshan Prefecture,Huaping County of Lijiang Prefecture,and western Dehong Prefecture.Besides,the short-time heavy precipitation mainly occurs between evening and early morning.The convective clouds related to the short-time heavy precipitation caused by the shear lines over Yunnan Province can be divided into four types:newborn convective cloud clusters,M_(α)CS,M_(β)CS,and banded MCS,among which,M_(α)CS and M_(β)CS result in 75%of the short-time heavy precipitation processes.In M_(α)CS and M_(β)CS,the cold cloud with temperature below–32℃is elliptical and they cover respectively 18,000 km^(2) and 104,000 km^(2).Besides,one or two centers exist in the elliptical cold cloud,and the central cloud top brightness temperature is lower than–52℃.Averagely,the duration of M_(α)CS is 3.3 hours,with the longest lasting for 6 hours.Meanwhile,the average duration of M_(β)CS is 2.3 hours,with the longest lasting for 5 hours.Short-term heavy precipitation occurs either around M_(α)CS and M_(β)CS centers or in the gradient maximum valued regions in the development direction.The coupling between low-level and upper-level circulation systems,the conditions for the occurrence of the convections,the occurrence and extinction of the MCS,and the characteristics of precipitation are comprehensively analyzed so as to establish the conceptual models for four kinds of the short-time heavy precipitation processes caused by the shear lines,which also provides the key technologies for the forecast of the short-time heavy precipitation in Yunnan Province.