四川盆地一次春季暴雨的特征分析和数值模拟

Characteristic Analysis and Numerical Simulation of a Spring Rainstorm in Sichuan Basin

利用地面自动站、高探空资料和NCEP再分析数据以及WRF模式,对发生在四川盆地的一次春季暴雨过程进行了基本特征分析和数值模拟研究。结果表明,暴雨发生在伴随高空急流波动的中低层短波槽和中小尺度系统十分活跃、低纬度环流系统稳定的形势背景下,暴雨存在多个落区,其影响系统和触发机制各不相同。暖区暴雨的触发系统初始扰动主要是与江南切变线活动有关的东风倒槽,对流不稳定区地形对加强的偏东气流强迫是盆地西部沿山暴雨形成的主要原因,南支高空急流与东南风低空急流的垂直耦合为暴雨系统的发生发展提供了有利条件,暖平流引起的低层高能高湿和对流不稳定与弱垂直风切变是暴雨系统发生发展的主要环境条件。数值模拟表明,尽管WRF模式系统对暴雨发生的低层热力和水汽输送以及沿短波槽分布的短时强降水落区、强度模拟基本正确,但过度估计了锋面降水的强度,对无或弱斜压强迫的暖区暴雨造成漏报。主要原因是较大尺度锋面降水影响系统能够被模式所分辨,而对暖区暴雨不稳定能量触发系统初始扰动发展的模拟能力有限。

Based on hourly observation data from surface Automatic Weather Stations(AWS),sounding data,NCEP reanalysis data and WRF model,the basic characteristics and numerical simulation of a spring rainstorm in Sichuan basin are analyzed.The results show that the rainstorm occurs under the background that the middle and low level short-wave trough and meso-micro scale system are very active with the fluctuation of upper jet,and the circulation system of low latitude is stable.There are multiple precipitation zones of the rainstorm,and impact systems and trigger mechanisms are different.The initial disturbance of the triggering mechanism of the warm-sector rainstorm is the easterly inverted trough which is related to the shear line activity in the south of the Yangtze river.The main reason for the formation of the rainstorm along the mountain in western Sichuan basin is that the terrain forcing on the strengthened easterly airflow in the convection-unstable region.The vertical coupling between the upper jet of the south branch and the lower jet of the southeast provides favorable conditions for the?generation and development of the rainstorm.The high energy and high humidity in the lower layer,convective instability caused by warm advection and weak vertical wind shear are the main environmental conditions for the occurrence and development of rainstorm.Numerical simulation indicates that,although low-layer heat and water vapor transmission of rainstorm,as well as the area and intensity of short-term heavy rain along the short-wave trough are simulated correctly by the WRF model system,the intensity of frontal precipitation is overestimated and the warm-sector rainstorm without or weak baroclinic force is failure predicted.The main reason is that influence system of the large scale frontal precipitation can be distinguished by the model,and the ability to simulate the development of the initial disturbance is limited,which triggers system of unstable energy of the warm-sector rainstorm.