高强度降水过程形成和发展的一种机制分析

Study on the Mechanism of Formation and Development of a Highly Intensive Precipitation Event

应用Sawyer Eliassen次级方程诊断分析了一次高强度降水过程中的湿球位涡场,结合诊断结果探讨了高强度暴雨形成和发展的原因。分析表明:条件性对称不稳定是这次强降水发生的不稳定机制之一。由强盛的西南低空急流输送的水汽在雨区低层辐合,地转动量近似下的锋生强迫形成的锋面次级环流促使暖湿空气向上输送,使聚集在其内的不稳定能量得以释放,导致强降水发生。

The paper diagnoses the wet bulb potential vorticity field,and analyzes the structural characters of the frontogenesis secondary circulation of a highly intensive precipitation event in 21th—25th July 2002 using the Sawyer-Eliassen secondary equation.Then based on above results,this paper discusses the formation and development mechanism of the event.The analysis shows that conditional symmetric instability might be the unstable mechanism responsible for the heavy rain event.A great deal of moisture carried by the strong southwest low jet was converged in the low layer of rain region,under the geostrophic momentum approximation,the frontogenetical secondary circulation driven by frontogenesis forcing made the warm and wet air ascend and the accumulated unstable energy released,thus leading to the occurrence of the intense precipitation.