NUMERICAL SIMULATION OF EXTREMELY HEAVY RAIN AND MESO-β SCALE LOW VORTEX IN INVERTED TYPHOON TROUGH

摘要

Large-scale and mesoscale analyses are made for extremely heavy rain (EHR) and meso-β scale low vortex (MSLV) in Jiading District of Shanghai Municipality during 6 - 7 July 2001. It is shown that the EHR forms in the situation of northern westerly trough linking together with southern inverted typhoon trough at northwest side of the West Pacific Ocean subtropical high. Numerical simulation is made using a 21-layer improved REM (regional η-coordinate model) for this course. The results show that the precipitation forms earlier than MSLV, and the strong convergence in wind velocity mate (WVM) triggers the strong precipitation. The formative reasons of WVM, especially the weak wind velocity center are discussed, and the formative mechanisms of the MSLV and EHR are discussed using high spatial and temporal resolution model-output physical fields. The results show that the heavy rain releases latent heat and warms the air column, and enhances the low-level positive vorticity that existed before. Then it causes the formation of MSLV. There is a positive feedback mechanism between low vortex and precipitation, so CISK must be an important mechanism.