Tides play a crucial role in regulating the dispersal and dynamics of a river plume. However, the impact of tides on the dynamics and transport of freshwater in a medium-scale river plume, particularly with multiple outlets, is still not well understood. Using the Hanjiang River Plume in the northern South China Sea as an example, we analyze the momentum and volume of the plume based on salinity space. We also investigate the effects of tidal advection and tidal mixing. Tidal advection propels plume water from the bulge downstream, resulting in a plume type with intermediate surface-advected and bottom-advected characteristics. Tidal mixing causes the plume to come into contact with the seafloor, leading to bottom-advected plumes. Tidal advection leads to the accumulation of plume water in high salinity space, while tidal mixing mitigates this effect, as the plume water near the estuary with relatively low salinity is effectively mixed. In the absence of tidal forcing, vertical shear is the main contributor to the total freshwater flux. However, when tidal effects are taken into account, the contribution of vertical shear to the total freshwater flux decreases and becomes comparable to the advection term. The downstream buoyant flow is primarily controlled by geostrophic balance. The barotropic current carries freshwater downstream, overpowering the upstream transport by the baroclinic current, resulting in a net downstream freshwater transport. Tidal advection enhances this downstream freshwater transport, while tidal mixing has the opposite effect.

中文翻译：

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潮汐对多出口中等规模河流羽流动力学和淡水输送的影响

潮汐在调节河流羽流的扩散和动态方面发挥着至关重要的作用。然而，潮汐对中等规模河流羽流（特别是具有多个出口的河流羽流）的动力学和运输的影响仍不清楚。以南海北部汉江羽流为例，基于盐度空间分析羽流的动量和体积。我们还研究了潮汐平流和潮汐混合的影响。潮汐平流将羽流从下游的隆起处推动，形成具有中间表面平流和底部平流特征的羽流类型。潮汐混合导致羽流与海底接触，导致底部平流羽流。潮汐平流导致羽流水在高盐度空间积聚，而潮汐混合则减轻了这种影响，因为河口附近盐度相对较低的羽流水被有效混合。在没有潮汐力的情况下，垂直剪切是淡水总通量的主要贡献者。然而，当考虑潮汐效应时，垂直切变对总淡水通量的贡献减小，并变得与平流项相当。下游浮力流主要受地转平衡控制。正压洋流将淡水向下游输送，压倒斜压洋流向上游的输送，从而导致净下游淡水输送。潮汐平流增强了下游淡水输送，而潮汐混合则具有相反的效果。