秦岭南侧一次弱对流暴雨过程机理分析

Mechanism Analysis of A Weak Convective Rainstorm Process in South Side of Qinling Mountains

使用地面自动站资料、常规观测资料、NECP再分析资料、卫星TBB云图资料等,通过天气学分析及动力能量诊断分析对2011年8月3～5日汉中、安康一次区域性暴雨过程进行机理分析.结果表明,这次过程东亚中高纬度维持大槽大脊环流形势,高原上东移的低涡直接影响陕西省,陕南大部处在低涡东侧,副高584 dagpm线在河南一带呈“凸”型,陕南位于“凸”型结构西侧,有利于低涡输送的水汽和能量在此地汇集；前期水汽条件输送和堆积条件不是特别良好,后期水汽逐渐上来,低层700 hPa切变线和850 hPa陕南偏南风急流在过程中对水汽输送和堆积贡献很大；动力因子方面高层强辐散、低层弱辐合产生的上升运动十分强盛,但K指数和θse分布表明暴雨区附近不稳定形势比较弱,且暴雨发生时并没有明显的强对流机制迹象,说明暴雨触发机制中不稳定能量的大小比有利的上升运动意义更大；云图分布上,对流发展与强对流过程相比要弱,云团没有达到MCC级别,预报员易忽略雷暴天气的发生；云因发展最旺盛时刻同时也是暴雨最大时段,TBB中心与暴雨中心对应比较一致.

Based on data of automatic weather station, conventional observation, NCEP reanalysis , and satellite TBB images, a regional tor- rential rain event occurred in Hanzhong and Ankang during August 3 -5,2011 was analyzed through synoptic analysis and dynamic energy di- agnosis method. The results showed that during this event high latitude of east Asia maintained large tank ridge circulation situation, the plat- eau vortex which moving eastward directly affect Shaanxi, and southern Shaanxi was in east of vortex ; the 584 lines of subtropical high which near Henan was ＂convex＂ type, and southern Shaanxi was in west of the ＂convex＂ type structure, which conducive to transfer water vapor and energy together. The water vapor transportation and accumulation conditions was not particularly good, later water vapor came up gradually, the shear line at 700 hPa and the southerly jet at 850hPa in the process contributed to it a lot. In the aspect of power factor, ascending motion which the structure of severe divergence in high and weak convergence in low produced was very strong, but the K index and the 0se distribu- tion showed that the rainstorm area near the unstable situation was relatively weak, and there was no signs of deep convection mechanism in storm, that showed the energy instability in rainstorm triggered mechanism had greater significance than favorable upward movement. Mean- while, the infrared cloud images indicated the development of convection was too weak to help the cloud reach MCC level, forecasters may o- verlook the thunderstorm weather; the time that cloud developed to the most exuberant was also the maximum period of rainstorm, TBB center and the rainstorm center corresponded consistent.