自由表面海洋环流模式的正、斜压模分解算法

A Barotropic-Baroclinic Mode-splitting Algorithm in the Free Surface Oceanic General Circulation Model

大气物理研究所海洋环流模式（IAPOGCM）特点之一是消除“刚盖”近似，引入海面起伏作为模式的预报变量。为此，是设计有效的时间积分方案，以克服模式中所保留的表面重力被对时间步长的苛刻限制．本文绘出了适应过程中流场正压和斜压模分解算法。研究表明，把海洋模式适应过程进一步分解为与海面起伏相联系的正压模和与密度不均匀分布相联系的斜压模，用不同的时间步长数值来解，计算效率可提高数倍以上．文中用四层IAPOGCM在北太平洋区域定量地比较了节省计算时间的有效性，并给出数值计算实例。

An oceanic general circulation model develoPed at the Institute of AtmoSPheric Physics (IAP oGCM) is free from the rigid-lid upper boundary condition but free surfaee is incorporated so that the model Permits the explicit treatment of sea level as a prognostic variable. In order to reduce the comput-er time, some stable and efficient time integration schemes have been developed. In this paper, a barotropic-baroclinic mode-splitting algorithm for such free surface OGCM is presented. It is shown that the computational efficiency can be increased several times by splitting the adjustment process fur-ther into the barotropic mode associated with sea surface elevation and baroclinic ones with inhomogcneous distribution of sea water density, and by numerically integrating these barotropic and baroclinic modes, respectively, with different time steps or different schemes. Experiment results are given to show its practicality and to quantitatively compare the computational efficienCy in time integration.