Hadley环流是低纬大气中重要的大尺度环流因子之一，它的变化对热带、热带外天气、气候变化有重要影响。然而目前对于Hadley环流变率主导模态成因、变化及季节间差异尚缺乏系统、深入的研究。本项目利用长期的观测资料，通过资料统计和动力诊断，并结合理论分析和数值模拟，围绕热带海温经向梯度是影响Hadley环流空间结构的重要因子，研究热带海温经向梯度在Hadley环流变率主导模态形成、变化中的重要作用，揭示热带海温经向梯度影响Hadley环流变率主导模态的过程和机理。在此基础上，探讨热带海温经向梯度在Hadley环流变率主导模态季节差异中的作用。相关工作的开展，将有利于我们增强对Hadley环流变化规律的认识，并且将为理解Hadley环流的气候效应提供科学参考，具有重要的科学意义。

The tropical Hadley circulation (HC) is one of the most important atmospheric circulations, which plays an important role in influencing the climate in the tropics and extra-tropics. However, there are no systemic analyses regarding the principal modes of the variability of HC, either of their causes, variations or the involved physical mechanisms. This project will address this issue, and focus on the potential impacts of the meridional gradient of tropical sea surface temperature (SST) on the HC, which is thought to be an important factor in influencing the spatial structure of HC. By using the long-term observation data sets, employing statistical analysis and dynamic diagnosis method, and combing with the theoretical analysis and numerical simulations, we expect to explore the possible roles of meridional gradient of tropical SST in the formation and variations of the principal modes of HC variability, and to discuss the relevant physical processes and mechanisms. On this basis, we will conclude the roles of tropical SST meridional gradient in the seasonal differences within the principal modes of HC variability. The implement of relevant work would not only improve the understanding of the variations of HC, also would provide some scientific references for further recognition of the climatic effects of HC, thus it would be helpful in both the scientific endeavor and practical significance.