南北向压强梯度力与太平洋赤道潜流的关系

赤道潜流（the Equatorial Undercurrent： EUC）对于大洋环流和全球气候变化有着重要的作用。赤道海区，随着科氏力逐渐趋向于0，地转平衡无法维持，赤道流系无法用地转理论描述。在很多研究中，ENSO、温跃层、海表高度、赤道风应力分布以及其他相关海气要素成为潜流研究的重点要素；压强可以视为温、盐、密、深的复杂关系映射，然而较少有研究将关注重点放在南北向压强梯度力上（the Northward Pressure Gradient： NGT）。在此，本文揭示了南北向压强梯度力的特定函数形式（the Function of Northward Pressure gradient： FNP）与赤道潜流的一个诊断关系。基于原始方程和尺度分析方法，我们得出了该关系的表达形式。结果表明：贝塔效应可能是造成FNP与赤道潜流密切相关的重要影响因子；赤道潜流的垂向结构部分受限于FNP的结构分布；对于赤道潜流来说，南北向压强梯度力相较于东西向压强梯度力更为重要。

Relationship between a function of the northward pressure gradient and the Pacific Equatorial Undercurrent

The Equatorial Undercurrent (EUC) plays an important role in ocean circulation and global climate change. Near the equator, as the Coriolis parameter goes to 0, equatorial currents cannot be described by geostrophy in which the pressure gradient force term is balanced by the Coriolis force term. Many previous studies focus on the relationships between the EUC and El Niño-Southern Oscillation (ENSO), the thermocline, sea surface topography, the distribution of equatorial wind stress and other atmosphere-ocean factors. However, little attention has been paid to the northward pressure gradient (NGT), which may also be important to the EUC. The pressure can be regarded as a complex nonlinear function of terms including temperature, salinity and density. This study attempts to reveal the connection between a function of the northward pressure gradient (FNP) and the EUC. The connection is derived from primitive equations, by simplifying the equations with using scaling analysis, and shows that the beta effect may be the main reason why the FNP is important to the EUC. The vertical structure of the EUC can be partially described by the FNP. The NGT has an obvious influence on the EUC while the eastward pressure gradient has a relatively smaller effect.