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    Reversed lateral circulation in a sharp estuarine bend with weak stratification

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    Article (3.053Mb)
    Date
    2019-06-13
    Author
    Kranenburg, Wouter M.  Concept link
    Geyer, W. Rockwell  Concept link
    Garcia, Adrian Mikhail P.  Concept link
    Ralston, David K.  Concept link
    Metadata
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    Citable URI
    https://hdl.handle.net/1912/24364
    As published
    https://doi.org/10.1175/JPO-D-18-0175.1
    Related Material/Data
    https://doi.org/10.26025/1912/26785
    DOI
    10.1175/JPO-D-18-0175.1
    Keyword
     Estuaries; Advection; Baroclinic flows; Barotropic flows 
    Abstract
    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.
    Description
    Author Posting. © American Meteorological Society, 2019. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 49(6), (2019):1619-1637, doi:10.1175/JPO-D-18-0175.1.
    Collections
    • Applied Ocean Physics and Engineering (AOP&E)
    Suggested Citation
    Kranenburg, W. M., Geyer, W. R., Garcia, A. M. P., & Ralston, D. K. (2019). Reversed lateral circulation in a sharp estuarine bend with weak stratification. Journal of Physical Oceanography, 49(6), 1619-1637.
     
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