Measurements of Enhanced Near-Surface Turbulence Under Windrows

Type Article
Date 2020-01
Language English
Author(s) Zippel Seth F.1, Maksym Ted1, Scully Malcolm1, Sutherland Peter2, Dumont Dany3
Affiliation(s) 1 : Woods Hole Oceanographic Inst, Woods Hole, Massachusetts, USA
2 : IFREMER, Univ. Brest, CNRS, IRD, Laboratoire d’Océanographie Physique et Spatiale (LOPS), IUEM, Brest, France
3 : Institut des sciences de la mer de Rimouski, Université du Québec à Rimouski, Rimouski, Québec, Canada
Source Journal Of Physical Oceanography (0022-3670) (American Meteorological Society), 2020-01 , Vol. 50 , N. 1 , P. 197-215
DOI 10.1175/JPO-D-18-0265.1
WOS© Times Cited 1
Keyword(s) Ocean, Atmosphere-ocean interaction, Boundary layer, Langmuir circulation, In situ oceanic observations, Surface observations
Abstract

Observations of waves, winds, turbulence, and the geometry and circulation of windrows were made in a shallow bay in the winter of 2018 outside of Rimouski, Québec. Water velocities measured from a forward-looking pulse-coherent ADCP mounted on a small zodiac show spanwise (cross-windrow) convergence, streamwise (downwind) velocity enhancement, and downwelling in the windrows, consistent with the view that windrows are the result of counter-rotating pairs of wind-aligned vortices. The spacing of windrows, measured with acoustic backscatter and with surface imagery, was measured to be approximately twice the water depth, which suggests an aspect ratio of 1. The magnitude and vertical distribution of turbulence measured from the ADCP are consistent with a previous scaling and observations of near-surface turbulence under breaking waves, with dissipation rates larger, and decaying faster vertically than what is expected from a shear-driven boundary layer. Measurements of dissipation rate are partitioned to within, and outside of the windrow convergence zones, and measurements inside the convergence zones are found to be nearly an order of magnitude larger than those outside with similar vertical structure. A ratio of time scales suggests that turbulence likely dissipates before it can be advected horizontally into convergences, but the advection of wave energy into convergences may elevate the surface flux of TKE and could explain the elevated turbulence in the windrows. These results add to a limited number of conflicting observations of turbulence variability due to windrows, which may modify gas flux, and heat and momentum transport in the surface boundary layer.

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