The Pearl River Estuary (PRE) is a bell-shaped estuary with a narrow deep channel and wide shoals. This unique topographic feature leads different dynamics of the subtidal estuarine circulation (SEC) in the PRE compared with a narrow and straight estuary. In this study, the nonlinear dynamics of the SEC in the PRE under mean circumstance are analyzed by using a validated 3-D numerical model. Model results show that the nonlinear advections reach leading order in the along-channel momentum balance. Modulated by tide, the nonlinear advections show significant temporal variations as they have much larger values during spring tide than that during neap tide. Unlike straight and narrow estuaries, both tidally and cross-sectionally averaged axial and lateral advections play important roles in driving the SEC in the PRE in which the axial advection dominates the nonlinear effect. But the two nonlinear terms balance each other largely resulting in a reduced nonlinear effect. Despite, the total nonlinear advection is still comparable with other terms and it acts as the baroclinic pressure to reinforce the SEC, especially during ebb tide, suggesting a flood-ebb asymmetry of the nonlinear dynamics in the PRE. In addition, diagnostic analyses of the along-channel vorticity budget show that nonlinear advections also make significant contribution to drive the lateral circulation in the PRE as Coriolis and baroclinic pressure terms, indicating complex dynamics of the circulation in the PRE.

中文翻译：

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珠江口潮下河口环流的非线性

珠江口（PRE）是一个钟形的河口，深河道狭窄，浅滩宽。与狭窄而笔直的河口相比，这种独特的地形特征导致了PRE中潮下河口环流（SEC）的不同动态。在这项研究中，通过使用经过验证的3-D数值模型分析了平均情况下PRE中SEC的非线性动力学。模型结果表明，非线性对流在沿通道动量平衡中达到领先顺序。受潮汐调制，非线性对流显示出明显的时间变化，因为它们在春季潮汐时的值比在潮汐潮时的值大得多。与狭窄的河口不同，潮汐和截面平均轴向和横向对流在驱动PRE中的SEC时都起着重要作用，其中轴向对流主导非线性效应。但是，这两个非线性项在很大程度上相互平衡，从而降低了非线性效应。尽管如此，总的非线性对流仍然可以与其他术语相提并论，它是增强SEC的斜压压力，尤其是在退潮期间，这表明PRE中非线性动力学的泛洪不对称。此外，对沿通道涡度预算的诊断分析表明，非线性对流也为推动PRE中的侧向循环（如科里奥利和斜压项）做出了重要贡献，表明PRE中循环的复杂动态。但是，这两个非线性项在很大程度上相互平衡，从而降低了非线性效应。尽管如此，总的非线性对流仍然可以与其他术语相提并论，它是增强SEC的斜压压力，尤其是在退潮期间，这表明PRE中非线性动力学的泛洪不对称。此外，对沿通道涡度预算的诊断分析表明，非线性对流也为推动PRE中的侧向循环（如科里奥利和斜压项）做出了重要贡献，表明PRE中循环的复杂动态。但是，这两个非线性项在很大程度上相互平衡，从而降低了非线性效应。尽管如此，总的非线性对流仍然可以与其他术语相提并论，它是增强SEC的斜压压力，尤其是在退潮期间，这表明PRE中非线性动力学的泛洪不对称。此外，对沿通道涡度预算的诊断分析表明，非线性对流也为推动PRE中的侧向循环（如科里奥利和斜压项）做出了重要贡献，表明PRE中循环的复杂动态。提示了PRE中非线性动力学的泛洪不对称性。此外，对沿通道涡度预算的诊断分析表明，非线性对流也为推动PRE中的侧向循环（如科里奥利和斜压项）做出了重要贡献，表明PRE中循环的复杂动态。提示了PRE中非线性动力学的泛洪不对称性。此外，对沿通道涡度预算的诊断分析表明，非线性对流也为推动PRE中的侧向循环（如科里奥利和斜压项）做出了重要贡献，表明PRE中循环的复杂动态。