斜压性对地转动量Ekman流的影响——理论分析

THE EFFECTS OF BAROCLINICITY ON THE GEOSTROPHIC MOMENTUM EKMAN FLOW——THE THEORETICAL ANALYSIS

本文研究了斜压效应对地转动量Ekman流的影响。利用两变量奇异摄动方法求得了边界层中风场及顶部垂直速度的前二级一致有效渐近解析解,解中明显地反映了斜压情形地转风随高度变化(即热成风)的影响,尤其是其中一级近似解完全由热成风影响所致。在边界层顶垂直速度的解中导出了三种由斜压效应引起的Ekmon抽吸新物理因子,即热成风形变、热成风涡度及热成风涡度交叉项等抽吸因子。分析表明,这些因子只在具有水平温度梯度不均匀的系统(譬如锋区)中方能出现。文中还对锋区内上述三种抽吸因子的动力特征作了具体的分析,指出在锋区这样的强斜压系统中,此三种抽吸因子的贡献是显著的。下一文中,我们将利用本文所得理论解对斜压效应进行具体的定量计算。

The effects of baroclinicity on the geostrophic momentum Ekman flow are investigated in this paper. By making use of the two-variable singular perturbation method, the uniformly valid asymptotic solutions of the first two orders of wind structure and the vertical velocity at the top of the boundary layer are obtained. The baroclinic effects are clearly reflected in these solutions. Especially, the first-order corrections of the solutions are completely induced by thermal wind. Three new pumping factors due to baroclinic effects are derived in the solution of vertical velocity at the top of the boundary layer. The first is thermal wind deformation, the second, thermal wind vorticity, and the third, the cross term of thermal wind vorticity. It is pointed out that only in such baroclinic systems of horizontally nonuniform temperature gradient as frontal zones will the three new pumping factors come into effect. Furthermore, the dynamic properties of the three pumping factors are carefully analysed with respect to a frontal zone. The quantitative results of the baroclinic effects will appear in the next paper.