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

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.