一次由气旋发展与边界层东北气流触发的强对流天气分析  

Analysis of a strong convective weather triggered by cyclone development and northeast airflow within planetary boundary layer

作　　者：赵桂香[1] 申李文[1] 闫慧[1] 邱贵强[1] ZHAO Guixiang;SHEN Liwen;YAN Hui;QIU Guiqiang(Shanxi Meteorological Observatory, Taiyuan 030006, China)

机构地区：[1]山西省气象台,山西太原030006

出　　处：《海洋气象学报》2020年第2期29-39,共11页Journal of Marine Meteorology

基　　金：国家自然科学基金项目(41475050);山西省科技厅应用基础研究项目(201701D221227)。

摘　　要：利用多种探测资料及NCEP/NCAR FNL 1°×1°再分析资料,对2019年4月24日发生在山西的大范围强对流天气进行了分析。结果表明:1)此次过程是在弱天气尺度强迫背景下,地面锋面气旋发展和低层偏东北气流伸入河套地区,触发了1个持续拉长状对流系统(persistent elongated convective systems,PECS)和1个β中尺度持续拉长状对流系统(meso-β-scale PECS,MβECS)发生发展造成的。2)与MβECS对应,雷达回波上表现为涡旋状的回波中镶嵌着多个对流单体,PECS则表现为4个线状回波和1个强降水单体风暴。雷达产品能更精细刻画较小尺度系统特征,但分类强对流的某些典型特征并不明显。3)物理量诊断揭示,低层锋生作用不仅使暖锋加强触发MβECS发展造成北部强对流,且使得冷锋加强和气旋发展,此背景下形成的边界层急流和地面中尺度系统导致中南部对流单体合并、加强并高度组织化。强对流范围和强度与涡旋或辐合线尺度及风场辐合强度密切相关,气旋内温压风湿场的扰动特征能更好地解释较小尺度系统形成发展的物理机制,且这些特征较强对流提前1~3 h出现,对强对流临近预报具有很好的指示意义。4)低层东北气流是干冷与暖湿空气的一个倾斜交界面,该面上各种要素并不均匀,围绕该支气流形成一个气旋式次级环流圈,是中尺度对流系统的重要触发机制;气流两侧存在较大纬向风垂直切变,是造成对流风暴传播、持续时间长的重要原因之一。A widespread severe convection weather in Shanxi on 24 April 2019 is analyzed based on a variety of observation data and NCEP/NCAR FNL 1°×1°reanalysis data.The results are as follows.1)Under the background of weak synoptic scale forcing,this event is caused by the development of surface frontal cyclone and the extension of low-level northeast airflow into Hetao area,which trigger the development of one persistent elongated convective system(PECS)and one meso-β-scale PECS(MβECS).2)On the radar echo,corresponding to the MβECS,there are many convective cells embedded in the whirling echo,while the PECS has 4 linear echoes and one heavy precipitation single-cell storm.Radar products can describe the characteristics of small-scale systems more precisely,but some typical characteristics of classified strong convection are not obvious.3)The diagnosis of physical quantities show that the low-level frontogenesis not only makes the warm front trigger the development of MβECS and cause strong convection in the north of Shanxi,but also makes the cold front strengthen and the cyclone develop.The boundary layer jet and the surface mesoscale systems induce the merging,strengthening,and highly organizing of the convective cells in the central and southern parts of Shanxi.The range and intensity of strong convection are closely related to the scale of the vortex or convergence line and the convergence intensity of wind field.The disturbance characteristics of temperature,pressure,wind,and humidity field in the cyclone can better explain the physical mechanisms of the formation and development of the smaller-scale systems,and these characteristics appear one to three h ahead of severe convection and have a good indication for the nowcasting of severe convection.4)The low-level northeast airflow acts as an inclined interface between dry and cold air and warm and wet air,on which various elements are not uniform.The formation of a cyclonic secondary circulation cell around this interface is an important trigger mechanism for

关 键 词：锋面气旋 倾斜交界面 线状回波 边界层急流 中尺度辐合线 

分 类 号：P458.3[天文地球—大气科学及气象学]