Numerical Simulation and Diagnostic Analysis of Rainstorm over Shaanxi Province during Early Summer
一次陕西初夏暴雨过程的数值模拟及诊断分析

The distribution of annual precipitation, which is affected by mountainous terrain, decreases from south to north in Shaanxi Province. Annual precipitation is 400-600 mm in northern Shaanxi and approximately 500-700 mm in Guanzhong. In the south, however, annual precipitation is 700-900 mm. In the Micang, Daba, and Qinling mountains of southern Shaanxi, as well as in the western mountains areas, annual precipitation reaches 900-1250 mm. In addition, this precipitation exhibits significant seasonal variation. Precipitation is significantly higher in summer than in other seasons, accounting for 39% to 64% of the entire annual precipitation, and is concentrated in northern Shaanxi. In early summer before late June to early July, heavy rainfall gathers in southern Shaanxi. Due to the sudden increase in local precipitation, rainfall prediction is difficult. The case of a heavy rainfall event occurring in southern Shaanxi and Guangdong during 2-3 Jun 2006 is examined. Data was acquired through a variety sources including observation analysis, numerical simulation, and diagnosis analysis.The effects of a short-wave trough at the bottom of a cold eddy at 500 hPa, a shear line at 700 hPa, and a surface easterly are examined. The main factor triggering this storm was a sudden increase in the southeastward jet at 925 hPa and 850 hPa in the low troposphere. The process of this storm was simulated by the Weather Research and Forecasting (WRF) model. The results are essentially consistent with the actual precipitation values. The heavy rain area, the center of maximum precipitation, and vertical velocity are consistent with the observations. Moreover, present value potential vorticity analysis indicates that a very strong cold dry air mass propagating from the top of troposphere in this heavy rainfall process promoted the formation of severe precipitation. The change in vertical velocity and the general potential temperature and distribution of the abnormal convective vorticity vector (CVV), which were all obtained through simulation, accurately reproduce the area and changes in heavy rainfall. These three quantities demonstrate accuracy in forecasting the storm. Therefore, the CCV could be applied to forecast rainfall in Shaanxi Province.