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Three-Dimensional Wind-Driven Coastal Circulation past a Headland

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  • 1 Integrative Oceanography Division, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California
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Abstract

Local velocities and the trajectories of fluid parcels forced by wind blowing over a continental shelf, in the vicinity of a headland, are described with a linear, steady, three-dimensional barotropic model. The dynamical balance that governs the transport is similar to the wind-driven general circulation, because the varying bottom depth acts in the same way as meridional variation in the rotation rate. Far from the headland the circulation is independent of alongshore position, and the transport is parallel to the coast. The alongshore pressure gradient is a significant term in the alongshore momentum balance. Near the headland, the amplitude of the circulation, including the vertical motion, is larger on the upwave side (the side toward which a Kelvin wave would travel) than on the downwave side. On the upwave side, the flow adjusts to the presence of the headland over a distance of order δEB*, where δE is the ratio of the Ekman depth to the maximum shelf depth and B* is the width of the shelf. Fluid parcels that upwell on the upwave side are drawn from deeper depths than parcels that upwell at other alongshore locations. On the downwave side the flow adjusts over a relatively long distance, of order δ−1EB*.

Corresponding author address: Clinton Winant, Integrative Oceanography Division, Scripps Institution of Oceanography, University of California, San Diego, 9500 Gilman Dr., La Jolla, CA 92093. Email: cdw@coast.ucsd.edu

Abstract

Local velocities and the trajectories of fluid parcels forced by wind blowing over a continental shelf, in the vicinity of a headland, are described with a linear, steady, three-dimensional barotropic model. The dynamical balance that governs the transport is similar to the wind-driven general circulation, because the varying bottom depth acts in the same way as meridional variation in the rotation rate. Far from the headland the circulation is independent of alongshore position, and the transport is parallel to the coast. The alongshore pressure gradient is a significant term in the alongshore momentum balance. Near the headland, the amplitude of the circulation, including the vertical motion, is larger on the upwave side (the side toward which a Kelvin wave would travel) than on the downwave side. On the upwave side, the flow adjusts to the presence of the headland over a distance of order δEB*, where δE is the ratio of the Ekman depth to the maximum shelf depth and B* is the width of the shelf. Fluid parcels that upwell on the upwave side are drawn from deeper depths than parcels that upwell at other alongshore locations. On the downwave side the flow adjusts over a relatively long distance, of order δ−1EB*.

Corresponding author address: Clinton Winant, Integrative Oceanography Division, Scripps Institution of Oceanography, University of California, San Diego, 9500 Gilman Dr., La Jolla, CA 92093. Email: cdw@coast.ucsd.edu

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