Abstract The role of open boundary conditions in modelling the seasonal variation of the North Equatorial Current Bifurcation latitude (NBL) is studied based on a linear Rossby wave model, 1.5-layer reduced-gravity model and Hybrid Coordinate Ocean Model (HYCOM). For a regional ocean model that covers the western Pacific, it is found that the seasonal variation of the NBL can be well reproduced as long as the data at the open boundary is provided by the corresponding basin experiment, no matter where the location is. However, the south–north migration of NBL as well as its peak seasons is not properly simulated if we apply other types of data at the open boundary as its location is close to the west. Sensitivity experiments indicate that the bad performance is attributed to the over-specification error and incomplete adjustment of interaction between wind forcing and westward propagating signals from incompatible open boundary data. The performance gets better as we set the open boundary at proper location and choose suitable open boundary condition. These conclusions can be extended to the simulations of low-latitude western boundary currents.

中文翻译：

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区域模型中北赤道洋流分叉的季节变化：开放边界条件的作用

摘要 基于线性Rossby波模型、1.5层减重力模型和混合坐标海洋模型(HYCOM)，研究了开放边界条件在模拟北赤道洋流分岔纬度(NBL)季节变化中的作用。对于一个覆盖西太平洋的区域海洋模型，发现只要相应的盆地实验提供开放边界处的数据，无论位置在哪里，都可以很好地再现NBL的季节变化。然而，如果我们在开放边界上应用其他类型的数据，由于其位置靠近西部，则无法正确模拟 NBL 的南北迁移及其旺季。灵敏度实验表明，性能不佳的原因是来自不兼容的开放边界数据的风力和西向传播信号之间的相互作用的过度规范和调整不完全。当我们在适当的位置设置开放边界并选择合适的开放边界条件时，性能会变得更好。这些结论可以推广到低纬度西部边界流的模拟。