热带西北太平洋上层环流季节内变异特征与机理

The upper circulation of the northwest tropical Pacific Ocean plays an important role in the heat budget of the warm pool, cross-basin ocean energy and mass exchanges, and tropical climate variability. Existing researches were mainly focused on the low-frequency (seasonal and interannual) variations of the zonal flows (e.g. North Equatorial Countercurrent; NECC), and our understanding of its intraseasonal variability (20-90 day) and meridional flows (e.g. tropical cell; TC) is rather limited, due to the shortage of in-situ observation. Utilizing the high-quality, multi-station upper ocean current measurements by the Western Pacific mooring array during 2014-2016, in this project we attempt to provide a comprehensive investigation for the intraseasonal variability of the NECC and the TC in the northwest tropical Pacific Ocean and its relationship with Madden-Julian oscillation (MJO) events. The spatial structure and dynamic regime of the TC will also be examined. The physical processes driving intraseasonal variations will be investigated with numerical experiments of two state-of-the-art ocean general circulation models. The relative importance of MJO and ocean internal variability will be underscored. The proposed research will contribute to our understanding of the regional ocean dynamics and intraseasonal climate variability in tropical Pacific Ocean.

热带西北太平洋上层环流对维持暖池热收支、大尺度能量和物质交换、调控热带气候变化等起到了关键的作用。受观测手段的限制，以往学界对该海域环流的研究大多集中在纬向流(如北赤道逆流；NECC)的低频变化上(如季节和年际尺度)，对季节内变化(20-90天周期)研究较少，且对经向流（如热带经圈翻转环流；TC）研究极少。本项目拟利用2014-2016年西太平洋潜标阵列取得的8个站点的高质量海流数据，系统研究NECC和TC的结构特征和季节内变率，揭示其季节内变异的时空特征及与Madden-Julian oscillation(MJO)事件的联系，深入探讨调控NECC和TC季节内变异的关键物理过程。通过分析HYCOM和OFES数值实验结果，我们将揭示NECC和TC对MJO各种强迫因子的响应过程，研究海洋内部不稳定(特别是中尺度涡旋)对上层环流季节内变异所起的作用，阐明大气强迫与海洋内部不稳定的相对重要性。

热带西太平洋海洋环流系统对太平洋地区热量、水文分布具有重要的调控作用。研究该环流系统多尺度变异规律及其动力学机制，对于探索热带西太平洋内部洋流结构、揭示海气相互作用机理、提高模式预报准确度等具有重要的意义。在热带西太平洋布放的7套潜标阵列，已经获取了2014-2015年上层1000米温度、盐度和流速等连续宝贵记录，另有2套数据持续到2018年长达5年。基于这些资料，我们取得了以下研究成果：1）揭示了次表层纬向流的结构特征以及与表层北赤道逆流（NECC）的变异关系；2）证实了热带经圈翻转环流的结构和季节-年际变异规律；3）定量化揭示了热带西太平洋次表层环流对大气季节内振荡（MJO）的响应过程。本项目已发表3篇高质量SCI学术论文。