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首页> 外文期刊>Journal of Physical Oceanography >Reversed Lateral Circulation in a Sharp Estuarine Bend with Weak Stratification
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Reversed Lateral Circulation in a Sharp Estuarine Bend with Weak Stratification

机译：逆向横向循环在弱分层的急剧河口弯道中

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Although the hydrodynamics of river meanders are well studied, the influence of curvature on flow in estuaries, with alternating tidal flow and varying water levels and salinity gradients, is less well understood. This paper describes a field study on curvature effects in a narrow salt-marsh creek with sharp bends. The key observations, obtained during times of negligible stratification, are 1) distinct differences between secondary flow during ebb and flood, with helical circulation as in rivers during ebb and a reversed circulation during flood, and 2) maximum (ebb and flood) streamwise velocities near the inside of the bend, unlike typical river bend flow. The streamwise velocity structure is explained by the lack of a distinct point bar and the relatively deep cross section in the estuary, which means that curvature-induced inward momentum redistribution is not overcome by outward redistribution by frictional and topographic effects. Through differential advection of the along-estuary salinity gradient, the laterally sheared streamwise velocity generates lateral salinity differences, with the saltiest water near the inside during flood. The resulting lateral baroclinic pressure gradient force enhances the standard helical circulation during ebb but counteracts it during flood. This first leads to a reversed secondary circulation during flood in the outer part of the cross section, which triggers a positive feedback mechanism by bringing slower-moving water from the outside inward along the surface. This leads to a reversal of the vertical shear in the streamwise flow, and therefore in the centrifugal force, which further enhances the reversed secondary circulation.
机译：尽管对河曲的流体动力学进行了很好的研究，但对于曲率对河口水流的影响以及交替的潮汐流和变化的水位和盐度梯度的了解却很少。本文描述了在具有陡峭弯曲的狭窄盐沼小溪中曲率效应的现场研究。在分层可忽略不计的时期获得的主要观察结果是：1）潮退期间洪水的次要流量之间有明显的差异，如潮退期间河流中的螺旋形循环和洪水期间逆流，以及2）最高（潮汐和洪水）水流速度靠近弯道内部，与典型的河流弯道水流不同。河道速度结构是由于河口缺乏明显的点状条和相对较深的横截面来解释的，这意味着曲率引起的向内动量重新分配不能通过摩擦和地形效应的向外重新分配来克服。通过沿河口盐度梯度的对流，横向剪切的水流速度产生横向盐度差，洪水期间最咸的水靠近内部。所产生的横向斜压梯度力会在退潮时增强标准螺旋循环，但在洪水时会抵消它。这首先导致横截面外部洪水期间反向二次循环，这通过从外部将缓慢移动的水沿表面向内引入而触发了正反馈机制。这导致在流向中的垂直剪切力的逆转，并且因此在离心力的逆转中，这进一步增强了反向的二次循环。

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