一次副热带高压边缘切变线暖区暴雨特征分析

Features of a warm-sector shear line rainstorm on the edge of subtropical high

利用常规气象观测资料、NCEP 1°×1°再分析资料以及卫星和雷达资料,对2018年6月25—26日副热带高压(简称“副高”)边缘切变线暖区暴雨的大尺度环流背景、雨带的移动与传播、中尺度特征以及温湿特征等方面进行分析。结果表明:此次暖区暴雨过程是在副高稳定维持,500 hPa西风槽东移,并有低空急流配合,低空暖切变线触发不稳定能量释放的有利背景下产生的;暴雨落区位于700 hPa暖切变线和925 hPa暖切变线之间;暴雨期间,小尺度对流单体在鲁南地区触发,云顶亮温tbb≤-60℃,并沿引导气流向东北方向移动;强降水区域有多个强回波中心持续影响,有明显的“列车效应”,强回波持续时间长;红外云图能很好地反映天气系统的发生、发展和消亡,而水汽图像上色调暗区不明显,冷空气活动较弱;低层暖湿气流强烈发展,是造成此次暖区暴雨过程层结不稳定的主要原因;暴雨的水汽源地是孟加拉湾和南海,且强降水期间,随着西南暖湿气流的增强,水汽通量有一个跃增现象;云顶tbb≤-70℃覆盖的区域、水汽通量散度负值中心可以作为暖区暴雨落区预报的参考点。

Using conventional meteorological observation data,NCEP 1°×1°reanalysis data,FY-2G cloud imagery,and radar data,the large-scale circulation background,the movement and propagation of the rainband,mesoscale characteristics,temperature,and humidity features of the warm-sector shear line rainstorm on the edge of subtropical high from 25 to 26 June 2018 in Shandong are analyzed.The results are shown below.1)The warm-sector rainstorm process is generated under the favorable background of the stable and stationary subtropical high,the eastward movement of westerly trough at 500 hPa,the cooperation of low-level jet,and the unstable energy release triggered by low-level warm shear line.2)The rainstorm area lies between warm shear lines at 700 hPa and 925 hPa.3)During the rainstorm,small-scale convection cells are triggered in the south of Shandong Province and move northeastward along steering flow with the TBB at cloud top equal to or lower than 60℃.4)Multiple strong echo centers continuously affect the strong precipitation area with obvious train-effect and long duration of strong echo.5)Infrared cloud imagery can reflect the occurrence,development,and extinction of weather systems.The dark tone area in water vapor image is not obvious and the cold air is weak.6)The strong development of low-level warm and humid airflow is the main reason for the instability of stratification during the rainstorm process.7)The main sources of water vapor are the Bay of Bengal and the South China Sea.During the heavy precipitation,there is a jump in water vapor flux with the enhancement of warm and humid southwest air flow.8)The area covered by TBB at cloud top equal to or lower than 70℃and the negative center of water vapor flux divergence can be used as reference for warm-sector rainstorm forecast.