“99.8”山东特大暴雨形成机制的数值模拟分析

Numercial Simution of Forming Mechanism for the Torrential Rain in Shandong Province in August 1999

利用双重嵌套的非静力数值模式MM5V3，成功地模拟了1999年8月11～12日山东诸城发生的特大暴雨。利用模式输出的高时空分辨率资料，对这次暴雨天气及中尺度低涡的形成机制进行了诊断分析。结果表明，这次特大暴雨是在弱冷空气侵入台风低压环流，热带辐合带北伸的形势下形成的；倾斜涡度发展是特大暴雨及中尺度低涡产生、发展的重要机制，鲁东南有利的地形对中尺度低涡的形成具有重要作用；台风低压倒槽顶部的强辐合作用首先触发上升运动，产生强降水，强降水位于低层气旋性暖式切变最明显的地方；强降水释放的凝结潜热使高层气层增暖，高层辐散加强，引起低层中尺度低涡强烈发展，导致降水增幅。可见，CISK机制是特大暴雨和中尺度低涡加强的另一种机制。

The simulation was successfully made for the torrential rain process in Shandong province during 11-12 August 1999 using the two-way nested grid MMSV3 model. Using the simulated high resoulutin information, the forming mechanisms of the torrential rain and mesoscale vortex were analyzed. The results suggest that weak cold air spreading into typhoon circulation and tropical convergence streaching northward resulted in torrential rain. Slantwise vorticity development is an important mechanism that the torrential rain and mesoscale vortex occurred and developed. Beneficial terrain of southeastern of Shandong has important effect on the information of mesoscale vortex. Strong convergence on the top of the typhoon depression trough first triggered ascending motion and caused heavy rainfall. The heavy rainfall always lie where cyclonic shear is very evident. The releasing of latent heat from rainfall made upper atmosphere warm and resulted in intensifying of upper divergence, which made lower mesoscale vortex to develop intensively and amplified the rainfall. So CISK is another mechanism for torrentioal rain and mesoscale vortex development.