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Semi‐diurnal tidal ellipse variability in a region of freshwater influence
Author(s) -
Verspecht F.,
Simpson J. H.,
Rippeth T. P.
Publication year - 2010
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2010gl044470
Subject(s) - clockwise , stratification (seeds) , geology , water column , decoupling (probability) , inflection point , bay , shore , turbulence , tidal current , oceanography , mechanics , geometry , physics , seed dormancy , botany , rotation (mathematics) , mathematics , germination , control engineering , dormancy , engineering , biology
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.