The Influence of Wind Stress and River Runoff on a Shelf-Sea Front

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  • 1 Woods Hole Oceanographic Institution, Woods Hole, MA 02543
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Abstract

Runoff from land gives rise to the formation of a front-jet system separating fresher coastal waters from more saline waters offshore, over some continental shelves, notably in the Mid-Atlantic Bight in winter. Three first-order characteristics of such fronts are the anchor depth H, where the front intersects the bottom, the stretch l, i.e., the distance between its surface and bottom intersections, and the buoyancy contrast b across the front. The three characteristics may be determined from the cross-front property transfer rate, the along-front momentum balance, and the turbulence-energy dissipation rate. Key independent variables are the horizontal buoyancy transport Bx, the friction velocity u*, and direction θ of the wind, and the Coriolis parameters f. Simple approximate formulae connecting dependent to independent variables arewhere m, λ and μ are constants of order 300, 1 and 0.1 respectively. The entrainment rate across the front is μu2*f−1 cosθ, which is small compared to Ekman transport on some continental shelves, but possibly not on all.

Abstract

Runoff from land gives rise to the formation of a front-jet system separating fresher coastal waters from more saline waters offshore, over some continental shelves, notably in the Mid-Atlantic Bight in winter. Three first-order characteristics of such fronts are the anchor depth H, where the front intersects the bottom, the stretch l, i.e., the distance between its surface and bottom intersections, and the buoyancy contrast b across the front. The three characteristics may be determined from the cross-front property transfer rate, the along-front momentum balance, and the turbulence-energy dissipation rate. Key independent variables are the horizontal buoyancy transport Bx, the friction velocity u*, and direction θ of the wind, and the Coriolis parameters f. Simple approximate formulae connecting dependent to independent variables arewhere m, λ and μ are constants of order 300, 1 and 0.1 respectively. The entrainment rate across the front is μu2*f−1 cosθ, which is small compared to Ekman transport on some continental shelves, but possibly not on all.

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