Editorial Type:
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Article Type:
Research Article

Lateral Circulation Generates Flood Tide Stratification and Estuarine Exchange Flow in a Curved Tidal Inlet

Johannes Becherer Leibniz Institute for Baltic Sea Research Warnemünde, Rostock, Germany

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Mark T. Stacey Civil and Environmental Engineering Department, University of California Berkeley, Berkeley, California

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Lars Umlauf Leibniz Institute for Baltic Sea Research Warnemünde, Rostock, Germany

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Hans Burchard Leibniz Institute for Baltic Sea Research Warnemünde, Rostock, Germany

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Print Publication:
01 Mar 2015
DOI:
https://doi.org/10.1175/JPO-D-14-0001.1
Page(s):
638–656
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Abstract

Cross-channel transect measurements of microstructure and velocity in a well-mixed and curved tidal inlet in the German Wadden Sea show the occurrence of significant late flood stratification. This stratification is found to be a result of lateral straining. This study observes a strong single-cell lateral circulation, which is strongly pronounced at late flood and absent during most of ebb. This tidal asymmetry is caused by a systematic interplay between centrifugal forcing and the lateral baroclinic pressure gradient. During flood a positive feedback between the terms generates strong lateral circulation, whereas during ebb a negative feedback leads to a suppression of the cross-channel exchange. A theoretical framework based on vorticity is developed, which allows lateral and longitudinal circulation to be studied in a consistent way. With this framework it is possible to show that the tidal asymmetry of the lateral flow is a major driver of residual longitudinal estuarine circulation, here identified with the tidally averaged across-channel vorticity component.

Denotes Open Access content.

Corresponding author address: Johannes Becherer, Leibniz Institute for Baltic Sea Research Warnemünde, Seestraße 15, Rostock, D-18119, Germany. E-mail: johannes.becherer@io-warnemuende.de

Abstract

Cross-channel transect measurements of microstructure and velocity in a well-mixed and curved tidal inlet in the German Wadden Sea show the occurrence of significant late flood stratification. This stratification is found to be a result of lateral straining. This study observes a strong single-cell lateral circulation, which is strongly pronounced at late flood and absent during most of ebb. This tidal asymmetry is caused by a systematic interplay between centrifugal forcing and the lateral baroclinic pressure gradient. During flood a positive feedback between the terms generates strong lateral circulation, whereas during ebb a negative feedback leads to a suppression of the cross-channel exchange. A theoretical framework based on vorticity is developed, which allows lateral and longitudinal circulation to be studied in a consistent way. With this framework it is possible to show that the tidal asymmetry of the lateral flow is a major driver of residual longitudinal estuarine circulation, here identified with the tidally averaged across-channel vorticity component.

Denotes Open Access content.

Corresponding author address: Johannes Becherer, Leibniz Institute for Baltic Sea Research Warnemünde, Seestraße 15, Rostock, D-18119, Germany. E-mail: johannes.becherer@io-warnemuende.de
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