Semi-diurnal tidal ellipse variability in a region of freshwater influence

New insight into a key process, instrumental in the onset of stratification in tidally driven systems, is presented for the first time using long‐term field observations from the Liverpool Bay region of freshwater influence (ROFI). Tidal ellipses respond to changes in stratification, becoming more c...

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Bibliographic Details
Published in:Geophysical research letters 2010-09, Vol.37 (18), p.n/a
Main Authors: Verspecht, F., Simpson, J. H., Rippeth, T. P.
Format: Article
Language:English
Subjects:
Brackish
Computational fluid dynamics
Decoupling
Density
Earth sciences
Earth, ocean, space
Ellipses
Exact sciences and technology
Freshwaters
Oceanography
Progressions
Shear
Stratification
tidal ellipses
tidal straining
Turbulence
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Summary:New insight into a key process, instrumental in the onset of stratification in tidally driven systems, is presented for the first time using long‐term field observations from the Liverpool Bay region of freshwater influence (ROFI). Tidal ellipses respond to changes in stratification, becoming more circular with greater vertical structure, and reveal variability in response to tidal straining. An inflection point that occurs before the maximum vertical density difference, at the time of maximum positive bed‐surface cross‐shore shear, is identified as the crucial point where the water column abruptly decouples. The surface and bed layers then rotate in clockwise and anti‐clockwise directions, respectively. The maximum vertical stratification is observed when the maximum negative bed‐surface along‐shore shear is reached. Decoupling to a two‐layer system is therefore not the smooth progression predicted using turbulence closure models, but rather a very sudden switch, highlighting the importance of the role of Reynolds stresses.
ISSN:0094-8276
1944-8007
DOI:10.1029/2010GL044470