中文摘要：

利用ECMWF最新发布的Interim再分析资料，计算了东亚季风区Hadley环流质量流函数，并使用EOF分解、相关分析及合成分析等统计方法，分析了夏季东亚季风区Hadley环流上升支结构的异常特征及其对我国长江流域降水的影响。发现夏季东亚季风区Hadley环流上升支具有独特的双上升中心结构，两上升中心的位置分别对应东亚夏季风系统中的两条辐合带——热带季风槽及梅雨锋。上升支的主要异常模态表现为两个上升中心“跷跷板”型的反相异常。与梅雨锋对应的副热带上升中心强度与长江流域降水呈正相关关系，即当其偏强时，长江流域降水偏多，反之亦然。副热带支偏强时，低层西太平洋副热带高压偏南导致气流在长江流域异常辐合，其异常西南风水汽输送使得长江流域有异常水汽辐合，高层气流在长江流域异常辐散。同时鄂霍次克海附近阻塞活动偏强，东亚沿海地区500hPa高度场出现“＋-＋”的经向异常型。这些异常型均有利于长江流域的降水。

英文摘要：

Using interim reanalysis from ECMWF the monthly mass stream function of the Hadley cell over the Eastern Asia monsoon region is calculated, and the variation of anomalous ascending branch structure in the Hadley cell over the Eastern Asia monsoon （EAM） region and its impacts on the precipitation in the Yangtze River basin in summer are analyzed. It is found that there is a double-ascending-center structure in the ascending branch of the Hadley cell over EAM region in summer, and their locations coincide with the latitudes of the tropical monsoon trough and the subtropical Meiyu front respectively, which are the two major members of Eastern Asia summer monsoon system. The first EOF mode of the ascending branch anomalies show that the variations of the two ascending centers are out of phase. There is a significant positive correlation between the intensity of the subtropical ascending center which accompanies with the Meiyu front and the precipitation of the Yangtze River basin. This suggests the rainfall in the Yangtze River basin increases when this subtropical ascending center strengthens, and vice versa. The low-level West Pacific subtropical high is over the lower latitudes compared to its climatological location when the subtropical ascending center strengthens, which induces the anomalous convergence over Yangtze River basin, with corresponding anomalous water vapor convergence by southwest wind anomalies. In contrast, there is a divergence on the upper troposphere over Yangtze River basin. The associated strengthening Okhotsk blocking along with a positive-negative-positive meridional of geopotential height anomalies on 500 hPa are also favorable for the increasing precipitation in the Yangtze River basin.