南海西部夏季离岸流的年际及年代变异研究

The western boundary current region in South China Sea (SCS) is a key area for the ocean climate variability of the SCS. The heat transport in this region, which is caused by summer ocean circulation, can influence the ocean climate variability in the central and southern SCS and the climate of the SCS region througth the air-sea interface exchange. However, studies on the interannual to decadal variability of the summer offshore current in the western SCS are still quite scarce. This project is to futher study the interannual-to-decadal variability of the summer offshore current in the western SCS by using the statistical methods based on the oceanic data from insitu observations,satellite remote sensing and numerical outputs. This study is to reveal the structure and evelution process of this offshore current, as well as those of the associated dipole, and to discuss the impact of large scale atmospheric and oceanic forcings on the summer mesoscale circulation in the western SCS. The possible modulations of Pacific Decadal Oscillation and Indian Ocean Dipole on the summer mesoscale circulation will be studied and the dynamics for the varibility of the offshore current will be discussed. This project will promote the study of the SCS ocean circulation to a higher level and contribute to the study of the climate effect of marine ecosystem in the region.

南海西部边界流区是南海海洋环流变异的关键区域，该区夏季海洋环流变化导致的热量输送引起南海中南部海洋气候变异，并通过界面海气交换对南海周边地区的气候产生重要的影响。但迄今为止对该区夏季离岸流年际到年代变异的仍然很少。本项目拟采用卫星遥感、涡分辨模型输出、现场观测等高精度长期多源海洋资料，运用经验正交函数、回归分析、偏相关等多种统计方法，深入开展南海西部夏季离岸海流年际及年代变异研究，揭示该海流的三维结构、演变过程及其南北双涡结构的变化特征，阐明太平洋年代振荡（PDO）和印度洋偶极子（IOD）等对该区海洋环流变异可能的年际和年代调节, 探讨该海区夏季中尺度环流气候变异的机制，从而促进南海海洋环流变异研究更上新台阶,为进一步了解南海西部海洋生态系统的气候效应以及南海对我国气候变化的影响打好基础。

本项目采用卫星遥感海面高度、涡分辨模型结果、以及现场观测等多源海洋资料，运用经验正交函数分解、相关分析、能量收支等多种计算方法，1）开展南海西部夏季离岸海流的季节内变化与中尺度涡研究，探索南海西部离岸流的季节内特征。除了得到双涡结构模态之外，还发现一与上升流有关的新的离岸流模态。复经验正交函数分解得到的两个主要模态，反映了离岸流季节内信号的传播与中尺度涡旋活动有关。2）深入研究南海西部夏季离岸流的年际变化和年代调节。卫星遥感海面高度资料的两个经验正交函数模态分别代表由局地风场引起的年际变异和与海洋通道传入的准十年变异，后者可能与太平洋年代振荡相关。结合季节内、季节尺度的变异，重新阐述南海西部夏季离岸流的多尺度特征。3）基于1993-2017年OFES模式结果， 对应两种类型的西边界流事件，研究了南海西边界流区的涡动能（EKE）分布及其年际变异。EKE与Niño3.4相关分析表明，ENSO 事件一定程度上影响到研究海区EKE的年际变化。本研究的结果对于深入了解南海海洋环流的中尺度过程与变异、海洋生态系统的气候效应具有一定科学意义。