2011年长江中下游梅雨锋暴雨的环流特征分析

Analysis on circulation characteristics of Meiyu front rainstorm in the middle and lower reaches of Yangtze River in 2011

利用客观分析资料和常规观测资料,分析了2011年6月长江中下游梅雨锋暴雨的大尺度环流特征,并对其中两次梅雨锋暴雨过程的降水特征和锋生条件进行对比分析。结果表明:(1)500 hPa中高纬地区两槽一脊强度均比常年偏强,持续稳定的高纬经向环流形势的存在为梅雨锋强降水持续稳定提供了所需的冷空气,冷空气与印缅槽前稳定的西南气流在长江流域频繁交汇,有利梅雨锋锋生以及形成大范围持续性强降水;(2)200 hPa南亚高压北侧强西风急流以及其南侧东风急流均比常年明显偏强;(3)来自孟加拉湾的西南急流与副热带高压南侧偏强的东南气流辐合形成强南风影响我国华东地区,为梅雨锋强降水提供了充足的水汽输送,梅雨锋区水汽辐合明显加强时段与梅雨期四次强降水过程一一对应;(4)两次梅雨锋暴雨过程降水特征和锋生条件存在明显差异,前者冷暖空气同时对锋区作用造成能量锋区锋生,是一次对流性降水,后者无冷空气影响,是一次地面静止锋波动引起的稳定性降水。

Using the objective analysis data and observed rainfall,the large-scale circulation characteristics and the frontogenetical conditions of Meiyu front of the two intense rainstorm processes in the middle and lower reaches of Yangtze River in June 2011 are comparatively analyzed.The results are as follows：（1） the strength of two-ridge-one-trough on 500 hPa in middle and high latitudes regions was stronger than that in average years.Sustainable meridional circulation on high latitude provided the required cold air for Meiyu front rainstorm.The frequent intersection between cold air and the southwesterly flow from the Bay of Bengal was advantageous to the frontogenesis of Meiyu front and large-scale intense rainstorm.（2） The strength of westerly and easterly jets was obviously stronger than that in average years.（3） The southwesterly flow from the Bay of Bengal converged with the southeasterly flow which was on the southern periphery of the western Pacific subtropical high and formed the strong southerly flow providing sufficient water vapor for Meiyu front rainstorm.The periods of water vapor convergence corresponded to four intense rainstorm processes.（4） The precipitation characteristics and frontogenetical conditions of Meiyu front between the two intense rainstorm processes were obviously different.The joint action of cold and warm air caused the frontogenesis of Meiyu front in the former,whereas in the latter there was no cold air,and the precipitation was caused by stationary front wave.