南海混合层深度的季节变化及年际变化特征

Annual and Interannual Variations of the Mixed Layer in the South China Sea

通过分析新的SODA(Simple Ocean Data Assimilation)资料,得到南海混合层时空场的分布特征,剖析了南海混合层深度的季节及年际变化特征。资料分析表明:南海混合层存在着显著的季节和年际变化,且两者的均方差分布存在一定的差异。在季节变化中,冬季混合层在南海北部及西北陆架区深,在南海南部及吕宋冷涡处浅;夏季混合层在南海西北部浅,东南深。南海这种混合层深度分布特征除了与热通量的季节变化有关外,在相当大的程度上与季风引起的Ekman输送及Ekman抽吸有关。混合层深度距平场EOF(Empirical Othorgnal Function)第一模和第二模时间变化的主信号均为周期的年际变化信号,其中第一模态约为3 a,第二模态则有1.8,2.4和4.3 a的3个显著周期。EOF第一模显示混合层深度在南海东南部年际变化幅度最大,且滞后Nino3指数7个月时相关性最好(相关系数为0.422 3);EOF第二模显示在南海南部和北部混合层深度呈反位相变化。

Based on the new Simple Ocean Data Assimilation （SODA） data, the characteristics of the seasonal and interannual variations of the mixed layer in the South China Sea （SCS） are derived. There is a distinct difference between the seasonal and interannual variations of the mixed layer in the SCS. Generally, in winter, the mixed layer is deep in the north and northwest shelf of the SCS and shallow in the south and Luzon cold eddy region. In summer, the mixed layer is deep in the southeast and is shallow in the northwest, which is almost opposite to the pattern in winter. The seasonal variations of the mixed layer depth is mainly caused by the net heat flux, Ekman transport and Ekman pumping caused by monsoon. Both the first and second modes of the EOF analysis of the mixed layer depth anomaly indicate interannual variations. The main cycle for the first mode is about 3 years. For the second mode the main cycles are 1.8, 2.4 and 4.3 years. The maximum inter- annual variation lies in southeast SCS for the first mode which has a good correlation with Nino3 index when there is a lag of 7 months. There is an opposite variation of the mixed layer depth between the north SCS and south SCS in the second mode.