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High-resolution modelling of a large-scale river plume

机译：大型河羽的高分辨率建模

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Evolution of a large-scale river plume is studied numerically using the Massachusetts Institute of Technology general circulation model. The model parameters were set close to those observed in the area of the Columbia River mouth. The fine-resolution grid along with the non-hydrostatic dispersion included in the model allowed for the reproduction of detailed inner plume structure, as well as a system of internal waves radiated from the plume’s boundary. It was found that not only first-mode but also second- and third-mode internal waves are radiated from the plume at the latest stages of its relaxation when the velocity of the front propagation drops below an appropriate wave phase speed of internal baroclinic mode. The model output shows that the amplitude of these high-mode waves is of the same order as the leading first-mode waves, which in combination with the specific vertical structure (location of the maximum structure function beyond the pycnocline layer) creates favourable conditions for the generation of shear instabilities. High-resolution model output also reveals evidence of a fine internal structure of the plume characterized by the presence of secondary fronts inside the plume and secondary internal wave systems propagated radially from the lift-off area to the outer boundary. These structures intensify the mixing processes within the propagating plume with predominance of the entrainment mechanism developing on the lower boundary between the plume’s body and underlying waters. The scheme of horizontal circulation in the plume was reproduced by the methodology of Lagrange drifters released near the mouth at different depths.
机译：使用麻省理工学院的总循环模型对大型河羽的演化进行了数值研究。模型参数设置为接近在哥伦比亚河口地区观察到的参数。模型中包含的精细分辨率网格以及非静液压扩散特性允许再现详细的内部羽状结构，以及从羽状边界辐射出的内部波系统。已经发现，当前传播的速度下降到内部斜压模的适当波相速度以下时，羽流在其松弛的最新阶段不仅会辐射出第一模内部波，还会辐射第二模和第三模内部波。模型输出表明，这些高模波的幅度与前导第一模波的幅度相同，这与特定的垂直结构（最大结构函数位于比多菌碱层以外的位置）相结合，为剪切不稳定性的产生。高分辨率模型输出还显示出羽状内部结构精细的证据，其特征在于羽状结构内部存在次要前沿，次生内部波浪系统从提离区域径向传播到外边界。这些结构加强了在羽状流中的混合过程，其中主要是在羽状体与下层水体之间的下边界形成了夹带机制。羽状流中的水平循环方案是通过拉格朗日漂流器在靠近嘴部不同深度处释放的方法再现的。

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