赤道和热带北印度洋受到季风的显著影响，存在明显的季节变化；热带南印度洋通过印尼贯穿流接收到来自太平洋的海水输送，参与了全球大洋环流输运循环；南印度洋热带环流圈成为衔接印度洋季风性海洋环流与全球大洋环流输运带的核心环节。本申请立足于南印度洋热带环流圈，从海洋动力过程出发，分析其对热带印度洋温盐分布和区域气候变化的影响。借助航次观测、理论分析和数值模式实验，拟深入研究南印度洋热带环流圈的结构与低频变异机制，分析环流对海洋热盐输送的影响，探讨环流的低频变异和印度洋气候模态的关系；尤其是研究热带印度洋年代际调整如何影响年际气候模态（如印度洋偶极子IOD和印度洋海盆模态IOB）的形态、强度、极端事件等。这对进一步了解印度洋海洋环境与季风系统演变有重要意义。

The equatorial and northern tropical Indian Ocean (IO) circulation is unique from the other oceans due to the dramatic influence from the monsoon, featuring with significant seasonal variations. The Indonesian Throughflow transports warm and low salinity water from Pacific to the southern tropical IO (STIO), forming an important route of the global Great Conveyer Belt. Thus, the tropical circulation in the southern tropical IO become a key linkage between the monsoon circulation in the northern tropical IO and the global Great Conveyer Belt. This proposal aims to study the dynamics of the ocean circulation in the STIO and its effects on water mass exchanges, temperature-salinity distribution, and climate change in the tropical IO. Based on in situ observations, theory analysis, and numerical modeling, this application will investigate the structure and low-frequency variability of the ocean circulation in the STIO, as well as its impacts on thermohaline transport and climate modes in the tropical IO, such as Indian Ocean Dipole and Indian Ocean Basin Mode. In particular, we will investigate how the decadal variations in the tropical IO can affect the activity of interannual climate modes, including type, strength, and extreme event, which will improve our understanding on the evolutions of ocean environment and the monsoon system.