中文摘要：

利用多种观测资料和NCEP再分析资料,分析了2007年7月9—10日皖南特大暴雨过程中尺度对流系统（MCSs）的活动特征及其引发暴雨的天气背景和环境场特征,探讨了大别山和皖南山区中尺度地形对MCSs活动和暴雨形成的影响,并通过高分辨率的数值模拟、地形敏感性试验和对比分析,进一步研究了中尺度地形对MCSs活动及其降水的影响。结果表明,此次强降水过程形成的2个暴雨中心分别位于大别山东北侧和皖南山区北部,期间有4个MCSs活动,皖南特大暴雨是由2个准静止MCSs活动造成的。MCSs具有明显的日变化特征,在清晨出现日峰值,梅雨锋中低层辐合和高层辐散是MCSs形成和发展的主要原因之一。在梅雨锋东移南压的过程中,MCSs相对于中尺度地形的位置在不断地发生变化,地形上空盛行气流方向以及地形Fw数也在不断变化,地形通过不同的动力机制影响MCSs。高地形Fw数下,大别山主要通过山脉波影响下游的MCSs;低地形Fw数下,地形绕流和山脉波共同影响下游的MCSs活动。当MCSs移近皖南山区北坡时,地形有利于MCSs的形成和维持,其阻滞效应可减缓MCSs的移动,有利于皖南特大暴雨的形成。大别山和皖南山区中尺度地形对暴雨强度和分布有明显的影响,其构成的中尺度组合地形效应是皖南特大暴雨形成的重要原因。

英文摘要：

Using the multiple observational data and NCEP reanalysis data, the synoptic background, environmental field features and activity characteristics of mesoscale convective systems （MCSs） producing an extremely rainstorm in the southern part of Anhui Province on 9-- 10 July 2007 are analyzed. The effects of mesoscale topography like Dabie Mountain and Wannan mountainous areas on the MCSs activity and rainstorm formation are studied and investigated. Then the high resolution numerical simulation, top- ographical sensitivity experiments and comparison analysis are conducted to further deduce the role of me- socale topography in the activities of rainstorm-producing MCSs. The results are as follows. Two rain- storm centers are formed on the northeast side of Dabie Mountain and in the northern part of Wannan mountainous areas, respectively in the heavy pericipitation process, where four MCSs are formed. The ex- tremely heavy pericipitation in Wannan region is produced by two quasi-stationary MCSs. The MCSs is of obvious diurnal variations and its diurnal peak is in the early morning. The Meiyu frontal lower-level con- vergence and high-level divergence are main causes of the MCSs formation and development. In the south- east movement of the Meiyu front, the MCSs position relative to the mesoscale topography is variable and the predominant flow direction over the topography and the topographic F~ number is also changed contin- uously. The topographies exert influences on the MCSs through different dynamic mechanisms. Under the high topographic Fw value, the impact of Dabie Mountain upon the downstream MCSs mainly is through mountain waves. Under low topographic Fw value, the flows around the topography and the mountain waves have a combined effect on the downstream MCSs. The Wannan mountainous areas are favorable for the MCSs formation and maintenance when the MCSs move close to its north slope. The topographic bloc- king effect slows down the MCSs movement, which is beneficial to the formation of extremely rainstor