σ坐标系海洋模式中水平压力梯度的一种算法

A COMPUTATIONAL SCHEME OF HORIZONTAL PRESSURE GRADIENT IN OCEAN MODELS WITH σCOORDINATE SYSTEM

在有海底地形的海洋环流模式中．水平压力梯度的计算是一个困难的问题。在大陆架附近，海底地形变化很大．水平压力梯度的计算误差往往使计算不稳定．或者海流的计算结果不可信．美国普林斯顿大学的海洋模式（POM）在垂直方向采用σ座标系．这一问题尤为突出．POM水平压力梯度的计算方法为静力扣除法，此方法已有较高的精度．但作者对POM的数值计算方法进行分析后，发现该方法仍有可改进之处．以作者提出的有地形大气环流模式中水平压力梯度计算方法的原理为基础．设计了一种计算σ坐标系海洋环流模式中水平压力梯度的新方法．给出了详细的推导过程．利用POM对该方法进行了检验，并与POM的原方案作了对比．结果表明．由于提出的方法有明确的物理意义，故能有效地改进有地形海洋模式中水平压力梯度的计算精度．

in the ocean circulation models with steep bottom topography the computation of the horizontalpressure gradient is a difficult problenl. Near the land shelf, the topography slope is very steep. and the topography changes rapidly. Errors in the computation of the horizontal pressure gradient often cause the computational instability or the unbelievable ocean currents. The USA Princeton University ocean Model(POM )adopts the a coordinate system as the vertical coordinate; this problem is specially severe and important. POMuses the hydrostatic reduction scheme to compute the horizontal pressure gradient which has quite high accuracy already. However. the authors find after analyzing the scheme that the computational method in POMcould be further improved. In this paper the authors developed a new scheme of computation of the horizontalpressure gradient in the a coordinate ocean models based on the principle of numerical computation scheme ofthe pressure gradient in the atmospheric models with large and steep topography and by taking account of theconcrete situation of the ocean, the detailed derivation is given. By the use of the POM. the new scheme istested and compared with the original one of the POM. The results show that the new scheme can efficientlyimprove the accuracy of the horizontal pressure gradient computation due to its evident physical meanings.