山东省三次暖切变线极强降水的对比分析

Contrastive Analysis on Three Extreme Heavy Rainfalls Triggered by Warm Shear Line in Shandong Province

应用加密观测、常规观测、卫星云图和雷达探测的资料及NCEO/NCAR(1°×1°)再分析资料,对由东省三次极强降水天气进行了诊断和对比分析。结果表明,,低层暖式切变线和500 hPa西风槽是三次强降水的主要影响系统。强降水前低层大气高温、高湿、对流不稳定同,有较高的对流不稳定能量。低层暖式切变线辐合和暖湿平流产生的上升运动与地面辐合线附近产生的上升运动相叠加,触发对流不稳定能量释放,产生强对流,造成强降水。较强的风垂直切变使得对流有组织地发展。强降水期间,中高层弱的干冷空气侵入,使得对流不稳定加强,中高层具有高位涡的干冷空气入侵诱发低层中尺度涡旋发展,辐合上升运动加强。低层暖湿气流螺旋式辐合上升与中高层入侵的干冷空气相遇,水汽凝结率增大,降水强度增强。中高层干冷空气侵入的时段与极强降水的时段相对应。有利的地形对局地短时极强降水有重要作用。低层暖式切变线和500 hPa低槽的位置、强弱不同,中高冷空气的强度和入侵路径不同,对流云团的发生发展、内部结构和移动方向不同,造成强降水的地理位置和强度不同。

Abstract： By using dense convective observational data, satellite images, radar data and NCEP/NCAR （1°×1°） reanalysis data, the weather systems for the three extreme heavy rainfalls are diagnosed and analyzed. The results show that westerly trough at 500 hPa and low-level warm shear line are the main impact system for the three heavy rainfalls. Before the rainfalls, high temperature, high humidity and convection instability exist in lower atmosphere. The ascending movement caused by convergence of lowqevel shear line and the warm and wet advection and the surface wind convergence line trigger the release of convection instability energy, producing strong convection and extreme rainfall. The strong vertical wind shear makesconvection systematically develop. During the heavy rainfalls dry and cold airs invade from middle-upper level so that convection instability gets intensified. On the other hand, the dry and cold airs with high potential vortex intruding from middle-upper level induce mesoscale vortex to develop in low-level atmosphere so that convergence and ascending movement increase. That the warm and wet airs in low-level helically converge and encounter the dry and cold airs from middle-higher level, so the water vapour condensa- tion and rain intensity increase. The periods when the dry and cold airs intrude from middle-higher level correspond with the periods of extremely strong rains. Terrain plays an important part in local and short-time extreme heavy rainfalls. The position and intensity for 500 hPa westerly trough and 850 hPa warm shear line are different and the intensity and tracks of the dry and cold airs at upper level are different, the convective cloud＇s development, evolution, movement and internal structure are different, causing the difference of rainstorm areas and intensity.