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Orientation of coastal-zone Langmuir cells forced by wind, wave and mean current at variable obliquity

Published online by Cambridge University Press:  01 October 2019

K. Shrestha
Affiliation:
Mechanical Engineering Department, University of Texas at Dallas, TX 75080, USA
W. Anderson*
Affiliation:
Mechanical Engineering Department, University of Texas at Dallas, TX 75080, USA
A. Tejada-Martinez
Affiliation:
Department of Civil and Environmental Engineering, University of South Florida, FL 33620, USA
J. Kuehl
Affiliation:
Mechanical Engineering Department, University of Delaware, DE 19716, USA
*
Email address for correspondence: [email protected]

Abstract

Langmuir circulation, a key turbulent process in the upper ocean, is mechanistically driven and sustained by imposed atmospheric wind stress and surface wave drift. In addition, and specifically in coastal zones, the presence of a mean current – whether associated with tidal currents or large-scale eddies – generates bottom-boundary-layer shear, which further modulates the physical attributes of coastal-zone Langmuir turbulence. We show that the presence of bottom-boundary-layer shear generated by oblique forcing between the mean current, atmospheric drag, and monochromatic wave field direction changes the orientation of the resultant, large-scale Langmuir cells. A model to predict this resultant orientation, based on salient parameters defining the forcing obliquity, is proposed. We also perform a systematic parametric study to isolate the ‘turning’ influence of salient parameters, which reveals that the resultant Langmuir cell orientation is always intermediate to the imposed forces. In order to provide a rigorous basis for the results, we study terms responsible for sustenance of streamwise vorticity, and provide a theoretical justification for the observed results.

Type
JFM Papers
Copyright
© 2019 Cambridge University Press 

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