El Niño—Southern Oscillation（ENSO）是热带太平洋海气作用最强的年际信号，其变化会引起全球气候异常，对东亚季风具有重要影响。2000年后中部型El Niño频繁发生，其原因一直成为争论的焦点。作为影响赤道上层海水充放的重要变量，太平洋副热带-热带经向环流圈的内部经向翻转环流（STC）是副热带驱动热带的“海洋通道”。但关于其变异在两类El Niño（中部型和东部型）期间的差异及对两类El Niño的影响的研究十分缺乏，是亟待解决的前沿科学问题。本项目拟利用观测资料结合多源海洋再分析数据和数值实验，研究STC变异在两类El Niño期间的差异，阐明其如何调整控制混合层海温变化的温跃层反馈、水平平流反馈等动力过程，揭示STC对两类El Niño的影响和机理，对深刻理解ENSO循环具有重要的科学意义，为提高ENSO和东亚季风预测水平提供理论基础，具有重要的应用价值。

ENSO is the strongest air-sea coupled interannual signal in the tropical Pacific. Its variation can induce severe global climate change, and has significant impact on the eastern Asian monsoon. The occurrence frequency of the central Pacific El Niño has been increased since 2000. The reason becomes a focus of the debate. The interior branch of the Subtropical-Tropical Cells (STC), which is forced by the subtropical wind stress, plays an important role in the equatorial upper ocean variation. It is the “ocean tunnel” that links the tropic to the subtropic. This proposed program aims to understand the different variations of the interior STC during two types of El Niño (eastern type and central type), elucidate how the interior STC modulates the thermocline feedback and zonal/meridional feedbacks during the evolution of El Niño, and hence reveal the influence of it on the two types of El Niño as well as its mechanism, through observations (Argo etc.), ocean reanalysis data and numerical experiments. The study of this program is important to understand the ENSO variability, hence to improve the prediction of the ENSO and eastern Asian monsoon.