太平洋南赤道流的时空变异及其对印尼贯穿流的调控作用

The South Equatorial Current (SEC) is the key component of Pacific equatorial current system and important water sources of the Indonesian Throughflow. Thus, the significant spatial and temporal variabilities of the SEC are essential for global climate changes. The previous studies haven’t been able to cover the whole scope of the SEC due to the limitation of observations, and that, on the interannual time scale, only the influence of ENSO is concerned, while the modulation effects of IOD and PDO are ignored. Meanwhile, the contribution of SEC to volume transport between the Indian and Pacific Oceans tends to be underestimated. Recently, the Argo Program provides quasi-global and quasi-synchronous observations of temperature and salinity in the upper 2000m of the oceans since 2004, which are competent for studies of general ocean circulation and its variations. Based on the Argo data, the project plans to calculate the series of absolute geostrophic current in the upper 2000m of the tropical Pacific Ocean using the methods of P-vector and geostrophic approximation on β-plan. On this basis, the three dimensional structures as well as their seasonal and interannual variabilities of the SEC are revealed. Under the background of PDO, ENSO and IOD, the influencing mechanisms of local winds and long equatorial waves of the Pacific and Indian Oceans on the spatial and temporal variations of the SEC are to be expounded. Based on the in situ observations of temperature, salinity and current in the Indonesian Seas, by means of high-resolution model simulations, the water mass analysis, and passive tracer method, the pathways of SEC water in the Indonesian Seas are explored, and the modulation effects on ITF volume transport and characteristics are quantitatively evaluated.

南赤道流是太平洋赤道流系的主要组成部分和印尼贯穿流的重要水源之一，其高度的时空变异性对全球气候变化至关重要。以往的研究受观测资料限制无法涵盖整个SEC流域，年际尺度上也只关注ENSO的影响，忽略了IOD和PDO的调制作用，同时低估了SEC对印太海盆水体输运的贡献。最近，Argo计划提供了自2004年起准全球、准同步的大洋上2000m温盐观测资料，可胜任大尺度海洋环流及其变异的研究。本项目将基于Argo资料，利用P矢量和β平面地转近似，反演获得热带太平洋上2000m的绝对地转流。在此基础上，研究SEC三维结构及其季节和年际变化规律，阐明在PDO、ENSO和IOD背景下，局地风强迫和印太赤道长波对其时空变异的影响机制；利用印尼贯穿流关键海峡的温、盐、流现场观测，借助模式资料，通过水团分析、被动粒子示踪等方法，探究SEC海水在印尼海的运动路径，并定量评估SEC对ITF流量和水文特性的影响。

太平洋南赤道流（SEC）是热带太平洋环流的重要组成部分，也是印尼贯穿流（ITF）的重要水源之一，其时空变异对太平洋-印度洋洋际间的物质和能量交换有重要意义。本项目使用Argo温盐观测资料以及P矢量和赤道β平面地转近似方法反演得到了整个太平洋海盆的SEC资料，其振幅和变异规律与锚碇浮标观测的海流对比良好。基于此套海流资料，研究了太平洋SEC的三维空间结构及其季节和年际变异规律，发现SEC的变异信号存在自东向西传播的特征，这与太平洋纬向风异常密切相关。借助卫星观测的海表高度异常数据，发现西太平洋海盆SEC的变化与ITF出口处流量的变化相关性较好，说明能够影响热带东印度洋海温和海流的因素对太平洋SEC也具有潜在的调节作用。进一步研究发现，近年来南大洋表层增暖促使南印度洋整个副热带环流圈向极地偏移，导致大洋等密度面槽的两侧产生冷或暖信号，并经由东部海盆的经向翻转环流传播到热带印度洋，传播时间约为10年。可见，南大洋增暖对热带东印度洋海温和海流的年代际变异有重要影响，从而对西太平洋SEC的变异也具有潜在的调节作用，需进一步研究。另外，利用高分辨率模式输出海流资料和被动示踪方法，追踪得到了SEC流域的南太平洋热带水和南极中层水两种水团形成ITF的三维运动路径，发现太平洋SEC海水既是中、深层ITF的主要水源，也是上层ITF的重要来源，垂向平流在这其中起了关键作用。本项目的研究结果有助于深入理解热带大洋环流的动力机制以及洋际间的水体和热量交换，具有重要的科学意义。