利用非常规观测资料对上海特大暴雨过程的模拟研究

A Numerical Simulation of the Heavy Rainfall in Shanghai Using Non-conventional Observational Data

20 0 1年 8月 5～ 6日 ,上海市区出现了建国以来破记录的一次特大暴雨。天气形势分析表明 ,停滞在上海的热带低压和主体位于海上的西太平洋副热带高压为此次特大暴雨的发生提供了有利的环流背景 ,而低压内部特有的动力、热力结构及在其内发生发展的一系列中尺度对流云团与此次暴雨的发生有直接的关系。作者利用非静力中尺度数值模式MM5V3对此次暴雨过程进行了数值模拟研究 ,结果表明 :在非静力中尺度模式全物理过程的模拟中 ,采用牛顿张弛逼近法的四维资料同化方案来同化分析场和云顶亮温及上海地面气象自动站等非常规观测资料 ,模拟结果不仅基本上再现出大尺度及天气尺度系统的发展演变过程 ,而且还较好地模拟出了此次城市强暴雨过程的雨量空间分布及时序变化。因此 ,将较高时空密度的非常规观测资料用于高分辨率MM5中尺度数值模式 ,对于有效地预报城市灾害性暴雨是必要和有意义的。研究还揭示 :与热带低压相伴随的偏南暖湿气流不仅是此次暴雨过程的强水汽及热量输送带 ,而且也是热带低压和其内中尺度对流系统维持发展的必要条件 ;造成暴雨的中尺度对流系统垂直向上是一具有相对暖心、高湿且低空湿对流不稳定结构的气旋性涡旋 ,其内强上升运动与涡柱内低空辐合、高空强辐散密切联系。

The strong heavy rainfall occurred in Shanghai during 5～6 August 2001.Synoptic analyses indicate that the landed tropical cyclone(TC) and east to it, the western Pacific subtropical high were the favorable circulation conditions to this extraordinary heavy rainfall.The heavy rainfall was mainly associated with the mesoscale convective systems developing in TC.The nonhydrostatic mesoscale numerical model MM5V3 was applied to simulate this case.During the simulation, the non-conventional observational data, including automatic meteorological stations data and satellite data were directly adopted in nudging four-dimension data assimilation process of MM5V3.The simulated results implied that the prediction of heavy rainfall may be improved when non-conventional observational data were assimilated into numerical model.The simulation of the full physics processes of MM5V3 was basically possessed of a capability to reproduce the development and evolution of large-scale weather systems and tropical cyclone.The analysis of simulated results revealed that the specific dynamical and thermodynamical structures of mesoscale convective system in tropical cyclone were directly related to this heavy rainfall. The intense south wind jet stream below 500 hPa accompanying with the tropical cyclone was not only the favorable condition of the development and maintenance of the TC and convective cloud clusters, but also the moisture source and heat energy transport belt of this heavy rainfall.