Unraveling Interactions between Asymmetric Tidal Turbulence, Residual Circulation, and Salinity Dynamics in Short, Periodically Weakly Stratified Estuaries
Unraveling Interactions between Asymmetric Tidal Turbulence, Residual Circulation, and Salinity Dynamics in Short, Periodically Weakly Stratified Estuaries
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DOI：
10.1175/jpo-d-20-0146.1
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发表时间：
2021-02
影响因子：
3.5
通讯作者：
Xiaoyan Wei;H. Schuttelaars;M. Williams;Jennifer Brown;P. Thorne;L. Amoudry
中科院分区：
文献类型：
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作者：
Xiaoyan Wei;H. Schuttelaars;M. Williams;Jennifer Brown;P. Thorne;L. Amoudry
不对称潮汐湍流（ATT）强烈影响河口的健康和功能。然而，其对三维河口动力学的影响和水运动和盐度分布对ATT的反馈仍然知之甚少，特别是对于短河口（河口长度等于潮汐波长）。本研究首次系统地研究了在周期性弱层结条件下，短河口的上述相互作用。这是通过开发一个三维的半解析模型（结合扰动法与有限元法），允许解剖的ATT，河口环流，盐输运的不同过程的贡献。ATT的产生主要由应变诱导的周期性层结和不对称的底部剪切湍流所控制，它们对ATT的贡献在振幅和相位上都不同。与ATT和涡动粘剪协方差（SST）相关的剩余环流的大小约为重力环流（GC）的一半，并显示出与GC相反的模式。由应变引起的周期性层结产生的ATT有助于形成一个空间结构与GC相似的环流。这种环流降低了纵向盐度梯度，从而削弱了GC。相反，由于不对称的底部剪切产生的湍流的对流环流显示相反的模式GC和行动，以加强GC。在稳态盐度动力学方面，GC和潮汐泵对盐的输入同样重要，而环流则产生显著的向海盐输运。这些研究结果强调了确定ATT的来源，以了解其对河口环流和盐分布的影响的重要性。
Asymmetric tidal turbulence (ATT) strongly influences estuarine health and functioning. However, its impact on the three-dimensional estuarine dynamics and the feedback of water motion and salinity distribution on ATT remain poorly understood, especially for short estuaries (estuarine length ≪ tidal wavelength). This study systematically investigates the abovementioned interactions in a short estuary for the first time, considering periodically weakly stratified conditions. This is done by developing a three-dimensional semi-analytical model (combining perturbation method with finite element method) that allows a dissection of the contributions of different processes to ATT, estuarine circulation, and salt transport. The generation of ATT is dominated by (i) strain-induced periodic stratification and (ii) asymmetric bottom-shear-generated turbulence, and their contributions to ATT are different both in amplitude and phase. The magnitude of the residual circulation related to ATT and the eddy viscosity–shear covariance (ESCO) is about half of that of the gravitational circulation (GC) and shows a “reversed” pattern as compared to GC. ATT generated by strain-induced periodic stratification contributes to an ESCO circulation with a spatial structure similar to GC. This circulation reduces the longitudinal salinity gradients and thus weakens GC. Contrastingly, the ESCO circulation due to asymmetric bottom-shear-generated turbulence shows patterns opposite to GC and acts to enhance GC. Concerning the salinity dynamics at steady state, GC and tidal pumping are equally important to salt import, whereas ESCO circulation yields a significant seaward salt transport. These findings highlight the importance of identifying the sources of ATT to understand its impact on estuarine circulation and salt distribution.