北太平洋海表面高度的年际变化及其机制

Interannual sea level variability in the North Pacific Ocean and its mechanisms

利用15年(1993～2007年)月平均的海表面高度(SSH)异常资料,分析了北太平洋海表面高度的年际变化的时空结构,并研究了热通量和风应力两个因子对其的强迫作用.结果表明,北太平洋年际时间尺度SSH变化的大值区在黑潮延伸区和西太平洋暖池区.EOF分解第一模态的空间结构沿纬向呈带状分布,第二模态为沿经向呈带状分布.热通量强迫作用在中纬度的东北太平洋可以解释SSH年际变化40%以上.风应力对SSH的作用包括正压和斜压两个方面.正压Sverdrup平衡模型模拟的SSH年际变化较弱,仅能解释高纬度副极地环流西部的20%～40%.由大尺度风应力强迫的第一阶斜压Rossby波模型可以解释热带地区的20%～60%,中纬度中部的20%～40%,以及阿拉斯加环流东部和副极地环流西部的20%～60%.风应力强迫的一阶斜压Rossby波模型对SSH的强迫机理又可分为局地风应力强迫和西传Rossby波作用.其中,风应力的局地强迫作用(Ekman抽吸)在东北太平洋、白令海以及热带中部有显著的预报技巧,可以解释SSH年际变异的40%以上.Rossby波的传播作用在中纬度海域的副热带环流中西部和夏威夷岛以东起着重要作用,可解释20%～60%.

15 years （1993-2007） monthly-averaged sea surface height anomalies （SSHA） are used to analyze their interannual spatial and temporal variability, also their thermodynamic and dynamic mechanisms are studied. The prominent interannual variability is located in the Kuroshio Extension and the western Pacific warm pool. By using the EOF method, the first mode of interannual SSHA is more likely zonal, while the second is much more meridional. The steric SSHA induced by the heat flux explains more than 40% of interannual SSHA in the midlatitudinal northeastern Pacific Ocean. The time-varying barotropic Sverdrup balance could explain 20%-40% in the western Subarctic gyre, whereas their interannual variations are indistinctive. Among the baroclinic mechanisms, the first baroclinic Rossby waves model forced by large-scale wind stress could explain the interannual SSHA 20%-60% in the tropical Pacific, 20%-40% in the central midlatitudes, and 20%-60% in the eastern Alaska gyre and western Subarctic gyre, respectively. The interannual SSHA induced by the local Ekman pumping has a local structure, which could explain more than 40% of the observed changes in the northeast Pacific Ocean, likewise in the Bering sea and central tropical Pacific Ocean. The westward propagating Rossby waves, derived from the difference between the Rossby waves model and Ekman pumping model simulating SSHA, could explain 20% - 60% of the interannual SSH observations in the central and western subtropical gyre and east of the Hawaiian Islands.