9608号台风低压外围暴雨中尺度云团的发生发展

THE MESOSCALE TORRENTIAL RAIN CLOUD CLUSTER FROM THE LOW PRESSURE PERIPHERY AREA OF THE TYPHOON NO. 9608

1996年8月3～5日发生在河北省西南部的特大暴雨是在没有西风槽直接作用下由台风外围的3个中尺度对流云团造成的。云团发生在高能不稳定的弱斜压环境条件下,由台风外围的低空东南急流非地转重力波不稳定触发发展。暴雨区上空与东北地区西风槽之间有一水平尺度近1000km的垂直环流圈。Q矢量锋生函数计算分析表明,该环流圈形成了暴雨区与东北远距离的西风带系统之间的能量转换机制。水汽图分析表明,东北部的高纬小槽向东南转移,增强暴雨区上空对流高层反气旋辐散,使原生命史较短的暴雨云团再度发展,这对本次特强暴雨过程有一定的增幅作用。

The torrential downpour happened in southwest of Hebei Province in 3-5, August, 1996 was analyzed. It was caused by three periphery mesoscale convectional cloud clusters, which connected with Typhoon No. 9608, and had no direct impact from the westerly trough. They happened in high unstable energy and weak baroclinit condition. They were triggered by unsteady ageostrophic gravitational wave in the low-level jet from southeast of the outskirts of the typhoon. A perpendicular circulation cell about 1000 km in horizontal scale had developed between torrential rain area and the westerly trough to the northeast. Q-vector frontogenesis function analysis indicated that such circulation cell generated energy transforming system between torrential rain area and the distant westerly to the northeast. The analysis of water vapor imagery showed that the upper troposphere cyclone divergence above the torrential rain area was strengthened due to the movement of the high latitude short wave trough toward southeast. The lower torrential rain cloud cluster had redeveloped and had a magnificent reinforcing effect on the heavy rainfall process.