一次长江中下游梅雨锋暴雨过程的诊断分析

Diagnostic Analysis on a Meiyu Front Rainstorm Process in Midand Low-Reaches of Yangtze River

利用NCEP 1°×1°再分析资料、FY-2C卫星云顶亮温(TBB)和中尺度模式WRF输出的15km高分辨率资料,对2008年影响浙皖赣地区的一次梅雨锋暴雨过程进行了诊断分析。结果表明,青藏高原东侧西风槽和副热带高压之间的相互作用、对流层中低层切变线的维持以及低涡东移、发展是暴雨发生的天气尺度背景。TBB数据显示,在切变线附近不断有中尺度对流云团生成并东移、发展。与暴雨区相对应,在低空西南急流左侧存在多个β中尺度强水汽通量辐合中心,高空西风急流入口区右侧排列着一系列的辐散中心,表明该地区存在较强的水汽辐合上升运动。对流层低层高温高湿、中高层冷空气侵入,导致大气层结处于极不稳定状态。湿位涡的分布与中心位置对暴雨落区及强度具有较好地指示意义。暴雨区附近对流层高、低层都存在较明显的位涡水平平流,导致位涡扰动不断地自上游向下游地区移动。锋区前暖区的对流层中低层存在强垂直位涡柱,引发气旋性环流的发展,从而促进了辐合上升运动。

A Meiyu front rainstorm process is analyzed using NCEP 1°×1° reanalysis data,the temperature of black body and the high resolution output from WRF model.The results show that the large scale background is related to this rainstorm process including the interaction between westly trough and subtropical high,the existence of wind shear in mid-low troposphere and the eastward movement and development of low vortex.TBB data shows that the mesoscale convective cloud clusters continually emerge and develop eastwardly near the wind shear.In the corresponding rainstorm area,there exists multiple β mesoscale centers of moisture flux convergence in the left of lower level south-west jet and a series of divergent centers in the right of upper level west jet entrance,indicating that there is strong moisture convergence and upward motion in these areas.The high temperature and humidity in lower troposphere and colder air incursion in mid-upper levels make the atmosphere profile in steady state.The distribution of moisture potential vorticity and its center are good indicators for the location and intensity of rainstorm.The potential voticity（PV） advection near the rainstorm areas induce PV turbulence to move continuingly from upstream to downstream regions.The vertical column of PV in mid-low troposphere in warm sector can promote the development of cyclonic flow and upward motion.