WRF模式对江苏一次强降水过程的模拟分析

A case study of a heavy rainfall in Jiangsu with WRF model

摘要:

利用NCEP最终分析资料,使用WRF模式模拟了2008年7月22—23日出现在江苏的一次强降水天气过程。结果表明:WRF模式能较好地模拟出这次降水的区域,对这种中尺度天气系统具有良好的预报能力。在这次降水过程中,低空风场切变线和冷空气以及与高空急流的合理配置加强了强降水区垂直环流的发展,使降水区对流发展;而高空辐散、低空辐合的流场特征也促进了强降水的产生;这次过程的水汽输送在850 hPa上最强,850 hPa的强水汽输送是产生强降水必需的水汽条件;从能量方面看,江苏全境都处于K指数高值区,特别是江苏中北部有相当高的能量聚集,为强降水提供了不稳定条件。暴雨区上空螺旋度呈低层正中心、高层负值区的分布,螺旋度的高低层耦合是触发并维持低压暴雨的动力机制。

关键词:暴雨;数值模拟;K指数;WRF模式

Abstract:

〖WT5HZ〗Abstract:〖WT〗Based on the NCEP final analysis data,a mesoscale modelWRF was used to simulate a heavy rain process,which occurred in Jiangsu Province during 22—23 July 2008.The results show that the WRF has a strong simulating ability for precipitation as well as has a good capacity to predict the mesoscale weather systems.In this rainfall event,the rational allocation of lowerlevel wind shear,cold air and upper air jet stream strengthened the development of vertical circulations,which inspired the convection development in the rainfall region.Also,the upper air convergence and lowerlevel divergence in the large scale flow filed are favorable for the rainfall occurrence,where the strongest water vapor transfer from 850 hPa is necessary.On the basis of energy analysis,not only a high Kindex value all over the Jiangsu Province,but also substantial energy accumulation in the north and middle of Jiangsu provides the instability condition for the precipitation.In addition,the coupling of helicity with a negative(positive) value at upper(lower) levels is the dynamical mechanism to activize and maintain such a low pressure torrential rainfall.

Key words:precipitation;numerical modeling;Kindex;WRF model