南海北部海面高度的季节内变异及其传播特征 *

利用25年(1993—2017)的卫星高度计资料, 采用复经验正交函数(complex empirical orthogonal function, CEOF)方法, 分析南海北部海区海面高度季节内变异的时空分布及传播特征。标准差分析表明, 南海北部海面高度的季节内变异(intra-seasonal variability of sea level anomalies, SLA-ISV)在沿陆坡外侧区较强, 且SLA-ISV表现出明显的季节性变化, 冬半年强于夏半年。CEOF前两个主要模态能较好地揭示研究海区SLA-ISV的时空分布及其传播特征, 并表明SLA-ISV的强度受到季节性变化和年际变化的调制。全年CEOF的第一模态揭示SLA-ISV从台湾岛西南至西沙群岛以东区域的冬半年西南向传播特征; 而全年CEOF的第二模态则表现了SLA-ISV分别在台湾岛西南和东沙群岛西南的西南向传播特征。南海北部中尺度涡季节变化统计分析表明, CEOF的分解结果与南海北部的涡旋活动一致。

Intra-seasonal variability of sea level anomalies and their propagation features in the northern South China Sea from 25 years of satellite altimetry data

Intra-seasonal variability (ISV) of sea level anomalies (SLA) and their propagation features in the northern South China Sea (NSCS) are investigated using 25-year (1993-2017) satellite observations. The standard deviation of intra-seasonal SLA reveals that larger ISV exists in the northeastern South China Sea along the continental shelf/slope (200~2000 m) where it extends southwestward from Taiwan to Hainan. The ISV of SLA exhibits obvious seasonality, being strong in winter and weak in summer. By using Complex Empirical Orthogonal Function (CEOF) analysis, the spatial pattern and temporal variability of the ISV, as well as their inter-annual modulation, are studied. We find that there are mainly two types of ISV pattern, showing great agreement with eddy activities in the NSCS. The ISV of SLA is also modulated by seasonal and inter-annual variation. The first mode of CEOF indicates southwestward propagation of the ISV from southwest of Taiwan to east of the Xisha Islands, being especially strong in winter. The second mode of CEOF reveals two westward ISV regions: southwest to Taiwan and south to the Dongsha Islands. The statistical analysis for the seasonal variation of mesoscale eddies indicates that the CEOF results are consistent with the distribution of mesoscale eddy activities in the NSCS.