南海西边界流季节内演变过程的能量学诊断

项目名称： 南海西边界流季节内演变过程的能量学诊断

项目编号： No.40806006

项目类型： 青年科学基金项目

立项/批准年度： 2009

项目学科： 生物科学

项目作者： 庄伟

作者单位： 中国科学院南海海洋研究所

项目金额： 20万元

中文摘要： 本项目重点分析了南海西北边界流的季节内变化以及中尺度信号的传播特征。通过对遥感资料和涡分辨环流模型的综合分析，我们首次揭示了南海海平面的季节内变化特征及其机制，发现南海海平面的季节内变化存在四个显著区域。其中，泰国湾和南海北部陆架区的高频振荡主要反映了海洋对风场的正压响应，而吕宋海峡以西及越南以东的季节内振荡则是由环流的不稳定所激发的。能量收支分析进一步表明，南海内部平均能量和涡能量之间的能量转换十分活跃，平均流向涡旋的能量转换过程是南海内区涡能量的重要来源。我们进而采用最大相关系数方法研究了南海中尺度信号的传播特征，指出南海北部和西南部两条带状中尺度信号活跃区是涡旋传播的重要路径。北部带状区由涡旋受地形约束沿着南海北部陆坡地形向西南运动而形成，终年存在，但在冬季最活跃。南部带状区位于海盆的西南部，大致呈南北走向，主要反映了秋季西边界流的非线性效应导致的次级涡旋脱落过程。此外，本项目还通过个例分析，证实台风是影响南海上层环流高频变化的另一重要过程。不同路径和强度的台风过境前后，上层海洋流场的调整过程存在显著不同。

中文关键词： 南海；西北部边界流；季节内变化；能量转换

英文摘要： The intraseasonal variability (ISV) of northwestern boundary current and propagations of mesoscale signals over the South China Sea (SCS) are investigated in this project. With the synergy of remote sensing data and an eddy-resolving numerical model, we first reveal the intraseaonal variability of sea level over the SCS and note that there are four zones with strong　ISV. ISV in the Gulf of Thailand and over the northern SCS shelf is dominated by barotropic response to intraseasonal wind stress forcing. While to the west of Luzon Strait and the southeast of Vietnam, the dynamical instabilities are important for the generation of ISV. The energetic analysis suggests that the energy conversions between mean and eddy components are active in the SCS and the energy transfer from mean flow to transient flow is an important source of the eddy energy. We further use the maximum cross-correlation (MCC) method to study the propagation of mesoscale signals in the SCS. Significant mesoscale signals propagate along two major bands of high variability. The northern band is located west of the Luzon Strait, characterized by southwestward eddy propagation. Though eddies are the most active in winter, their southwestward migrations exist throughout the year, steered by bathymetry around the continental slope. The southern eddy band lies in the southwest part of the SCS deep basin and runs in an approximately meridional direction. The southward eddy propagation along this band mainly occurs in autumn and is likely related to the eddy detachments from the western boundary current due to nonlinear effects. In addition, the high-frequency upper ocean responses to typhoons are studies on the basis of two typhoon cases. The upper ocean flow displays significant but distinct responses to two typhoons with different tracks and intensities.

英文关键词： South China Sea; northwestern boundary current; intraseasonal variability; energy conversion