夏季东亚季风区Hadley环流经向结构变异及其对中国东部降水的影响

Several lines of evidence show that the Hadley circulation (HC) has poleward expansion since 1979. The expansion could result in poleward shifts of the subtropical dry zone and shifts in precipitation patterns affecting natural ecosystems, agriculture, and water resources. The main focus of this study is to show the meridional structure variation of the summertime regional Hadley cell in the eastern Asian monsoon region (EAMHC) and assess its potential implication for eastern China summer precipitation. To achieve this goal, the content of my research include: (1) Investigate the climatic characteristics of the meridional structure in EAMHC, and discuss its potential contributors such as land-sea contrast, Tibet Plateau, tropical SST by modeling experiments. (2) Examine the spatial-temporal features of abnormal meridional structure in EAMHC, and explain possible controls of tropical SSTA's on anomaly of the meridional structure of EAMHC, especially in the Tropical Indian Ocean,Pacific warm pool and the eastern equatorial Pacific sectors. (3) Study whether the meridional structure variation of EAMHC affects eastern China summer precipitation and its possible mechanism. The above analysis may therefore be of value in interpreting the change of EAMHC and in shedding light on predictable dynamics of the summer precipitation in China.

观测资料显示1979年以来Hadley环流（HC）有向极扩张的趋势，扩张所致的副热带干旱区向极移动和降水型重新分布将给人们的生产生活带来极大的影响。本项目试图弄清夏季东亚季风区HC经向结构变异及其对我国东部降水的影响，拟作以下研究：（1）夏季东亚季风区HC经向结构的气候特征，并利用数值模式探讨海陆分布、青藏高原及热带SST等因素在夏季东亚季风区HC独特经向结构形成中所起的作用。（2）夏季东亚季风区HC经向结构异常的时空特征，及热带海表温度异常（包括热带印度洋、西太平洋暖池及赤道东太平洋SSTA）对夏季东亚季风区HC经向结构变异的可能影响。（3）夏季东亚季风区HC经向结构变异对我国东部降水的影响及其可能机制。研究结果将有利于加深对东亚季风区HC变异的认识，为我国气候预测提供新的思路。

我国东部夏季降水异常的预测历来受到高度重视。本项目通过分析夏季东亚季风区HC经向结构的气候及异常特征，热带海表温度异常对夏季东亚季风区HC经向结构变异的可能影响，及夏季东亚季风区HC经向结构变异对我国东部降水的影响及其可能机制，为我国东部夏季降水的气候预测提供新的思路。所得主要结论为：（1）夏季东亚季风区HC的上升气流中存在热带支及副热带支两个中心，位置分别对应着东亚夏季风系统中的两条辐合带—热带季风槽及梅雨锋。其主要异常模态为热带支与副热带支“跷跷板”型的反相异常。（２）冬季热带印度洋的一致型SST异常对其后梅雨期的东亚季风区HC上升支异常有很好的指示作用。冬季热带印度洋全区一致型SST异常通常能持续到春夏季，导致菲律宾附近的对流活动减弱，激发向北的PJ波列，从而影响东亚季风区HC上升支异常。（3）夏季东亚季风区HC的副热带上升支与长江流域降水呈正相关关系。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。