滇中一次局地大暴雨雷达特征分析

Radar Characteristics of a Rainstorm in Central Yunnan Province

利用常规观测、加密自动站、NCEP 1°×1°每6h再分析资料和多普勒雷达等资料,对2017年6月20日发生在滇中的局地大暴雨进行分析。结果表明:低层700hPa切变线和地面辐合线是产生局地大暴雨的主要天气系统;局地大暴雨发生在低层辐合、中高层辐散的弱对流环境中,低层局地强水汽辐合为本次大暴雨提供了水汽条件;局地大暴雨发生在对流云团边缘TBB梯度最大的位置,暴雨发生前6h地面露点温度上升明显,同时对流有效位能CAPE也出现显著增加。本次强降雨过程先后出现两轮降雨高峰,第1轮强降雨持续时间长,雨强大,主要为强降水超级单体和中气旋造成;第2轮强降雨持续时间较短,雨强较弱,主要为多个对流风暴引发。两轮强降雨多普勒雷达图上为低质心结构,径向速度有逆风区形成,逆风区的出现比暴雨提前约1h,降水强度随着逆风区的消失而减弱。局地大暴雨发生地呈“喇叭口”地形,强降雨点位于山谷且三面环山,进入“喇叭口”山谷内的对流风暴在地面气旋和地形作用下稳定少动,是导致本次局地大暴雨的重要原因。

By using the conventional observation data,intensive autom atic station data,and the data of NCEP(1°X 1°,4 timesper day)and Doppler radar,a local heavy rain occurred in the central Yunnan on 20 June 2017 is analyzed.There sults show that the 700 hPa shear line and the ground convergence line were the main weather systems that produced the local torrential rain.The local torrential rain occurred in the weak convection environm ent where there were low-level converges and the middle-and upper-level diverges,and the strong local water vapor convergence in the lower level provided water vapor conditions for the heavy rain.The local to rren tial rain occurred in the area with the max imum TBB gradient at the edge of the convective cloud cluster.The surface dew-point temperature increased significantly 6 hours before the storm happens and CAPE also increased significantly.D uring the heavy rainfall process,there were two rainfall peaks:th efirst lasted for along period and m ainly caused by the heavy precipitation supercell and mesocyclone;the second lasted for a short period and was weak,mainly caused by multiple convectives torms.The Doppler rad arch arts of the two stages shows the low-centroid struc ture,and there was radial velocity formed in the upw ind zone,which was about 1 hour ahead of the storm.The precipitation intensity decreased with the disappearance of the upw ind zone.The local heavy rain occurred in aterrain,and the heavy rainfall occurred in avalley su rrounded by mountain sonthree sides.The stable and less movement of the convective storm in abell-shaped valley was an important reason for the local torrential rain.