Abstract: A series of three-dimensional numerical experiments of diagnosing global ocean circulation, based on the MOM4 global model, are used to investigate the sensitivity of global ocean circulation to vertical diffusivity. In the annual mean, vertical diffusivity has a considerable effect on the whole global ocean circulation system, especially in the equatorial Pacific region. Not only is the pattern of potential temperature greatly affected by vertical diffusivity, but also is the velocity field. As a whole, the horizontal and vertical temperature gradient is relative small along with the relative large diffusivity. Correspondingly，the south and north equator currents are rather strong, while the equatorial undercurrent and equatorial counter currents are relative weak. Moreover, each branch of equatorial system varies in their scale at the same time. Such a phenomenon demonstrates that the whole oceanic circulation is rather sensitive to the variation of vertical diffusivity. Furthermore, effects of each parameter in thermal equations within experiments are given. The physical mechanism is also discussed.

Key words: vertical diffusivity, global ocean circulation, sensitivity test, equatorial currents

摘要： 利用美国地球流体实验室的Modular Ocean Model（MOM4）模式构建了一组全球实际大洋环流实验，以检验海洋环流形势及温度结构对海洋垂直混合系数的敏感性，并仔细分析了各实验中温度方程中各项的变化，讨论了垂直混合系数改变对海洋环流形势影响的物理机制。实验结果表明，海洋垂直混合系数对海温的空间分布和海洋流场结构都有很大影响，这种影响在赤道温跃层附近表现得最为明显。这说明大洋环流对垂直混合强度的变化是相当敏感的。一般来说，在混合系数取值大的实验中大洋中上层温度的垂直和水平梯度都较小，相应的南北赤道流强度较强，赤道潜流和南北赤道逆流强度较弱，在混合系数取值小的实验中大洋中上层的温度梯度较大，此时南北赤道流强度较弱，赤道潜流和南北赤道逆流强度较强，赤道流系的各分支在范围上也有相应变化。

关键词: 垂直混合系数, 大洋环流, 敏感性实验, 赤道流系