一次台风远距离暴雨中的干侵入分析

Analysis on dry intrusion of a remote typhoon rain

利用常规观测资料和NCEP再分析资料，对2008年7月17-19日发生在山东地区的台风远距离暴雨过程进行了观测分析和模拟研究。结果表明：降水期间有来自中高层的干冷空气的侵入，主要有两种表现形式：对流层顶附近向下的干空气侵入和对流层低层由西北向南的干空气侵入。干侵入存在于300-600hPa之间，高层略微落后于低层，不利于对流不稳定的发展。但干冷空气侵入使得等相当位温面倾斜，有利于条件性对称不稳定的发展。干侵入使原来不饱和湿空气出现饱和，有利于降水增幅，雨区始终位于500hPa干区前沿。高层正位涡扰动沿相当位温密集带向低层输送，500hPa位涡高值区与降水有较好的同位相关系，对降水的发展和移动有一定的指示意义。

By using routine observation and NCEP reanalysis data, a typhoon remote heavy rainfall in Shandong province during 17-19 July, 2008 was diagnostically analyzed and simulated. The results show that the dry cold air intrusion process from mid-high level happened in this rainfall process can be classified into two forms： one is the dry intrusion from the top of troposphere while the other is from the lower layer of troposphere in the direction of northwest-north. The dry intrusion was located between 300- 600 hPa, and the upper levels are slightly behind the low ones, it was not good for the unstable develop- ment of convection. The unsaturated moist air turns to be saturated because of the dry intrusion, which led to the precipitation increasing, and the rain area was always located in the forefront of 500 hPa dry ar- ea. The disturbance of positive potential vorticity in the upper troposphere transporting downwards to the lower level along the intensive band of pseudo-equivalent potential temperature stimulated the develop- ment of the low-level mesoscale vortex. The in-phase relation between large-value potential vortieity at 500 hPa and precipitation implies the development and movement of the precipitation.