副热带高压边缘连续两次强降水形成机制分析

Analysis of the mechanism of two successive heavy rainfalls on the edge of subtropical high belt

利用常规观测资料、自动气象站加密观测资料、GPS/MET水汽监测资料、FY-2E卫星云图和NCEP/NCAR 1°×1°再分析资料,对副热带高压边缘山东南部连续两次强降水的形成机制进行分析。结果表明,两次强降水都是由副热带高压边缘500 h Pa弱西风槽过境影响产生的,副热带高压主体加强西移,850~700 h Pa有较强的西南急流。强降水产生在西南低空急流的前方、暖式切变线附近;西南低空急流加强北上强降水开始,急流减弱强降水结束。强降水区与CAPE的高值区、低层水汽通量高值舌、水汽辐合中心、暖平流中心有较好的对应关系。西南低空急流、GPS/MET水汽监测对强降水的短时预报有一定的指示性。对流云团TBB最低为-78^-62℃,各观测站对应最大小时雨量为40~90 mm。强降水期间,850 h Pa及以下有中尺度涡旋发展,涡旋尺度小,气压场上表现很弱,流场上表现明显,有明显的气旋性环流中心,在925 h Pa涡旋中心东南部的暖平流中心降水强度最大。第一次强降水的中尺度涡旋源地发展,稳定少动,在其东南部上升运动强且降水强度大;第二次强降水中,冷空气在低层从西北部侵入,形成气旋,向东北移动,强降水产生在冷锋前部的暖区中,对流不稳定能量高,降水强度大、范围大。

By using sounding and ground in situ observation data,GPS/MET and FY-2E satellite data,NCEP/NCAR reanalysis data（ 1° × 1°）,two severe rainfall events,which occurred on the edge of subtropical high belt in south Shandong,are analyzed. The results show that two heavy rainfall processes were both caused by weak westerly trough on the edge of the subtropical high at 500 h Pa,as the subtropical high belt strengthened and moved westward inducing southwesterly jets between 850-700 h Pa.Both heavy rainfalls occurred in the front of the southwesterly low level jets,and near the warm shear lines. As the low level southwesterly jets intensified and invaded northward,heavy rainfalls began,and while the jets weakened,the rainfalls eased. The torrential rain region has good consistency with the high value regions of CAPE,water vapor flux,convergence of water vapor and low level warm advection. Thesouthwesterly low level jet and atmospheric precipitable water retrieved from GPS/MET are indicative for short-time heavy rainfall forecast. The minimum TBB of convective cloud clusters were-78--62 ℃,corresponding hourly maximum rainfalls 40-90 mm. During the heavy rainfall process,a mesoscale vortex occurred below 850 h Pa with weak low pressure but significant cyclonic circulation. The most intense rainfall was generated at the center of warm advection in the southeast of the vortex at 925 h Pa. During the first heavy rainfall process,the mesoscale vortex moved less,while stronger rainfall was induced by stronger upward movement in the southeast of the vortex. During the second strong rainfall process,the low level cold air invaded from northwest into the vortex resulted in a cyclone, which moved northeastward. Large precipitation was produced in the warm zone in front of the cold front.