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Inner-shelf circulation is governed by the interaction between tides, baroclinic forcing, winds, waves, and frictional losses; the mean circulation ultimately governs exchange between the coast and ocean. In some cases, oscillatory tidal currents interact with bathymetric features to generate a tidally rectified flow. Recent observational and modeling efforts in an overlapping domain centered on the Martha's Vineyard Coastal Observatory (MVCO) provided an opportunity to investigate the spatial and temporal complexity of circulation on the inner shelf. ADCP and surface radar observations revealed a mean circulation pattern that was highly variable in the alongshore and cross-shore directions. Nested modeling incrementally...
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Current measurements from a vector-averaging current meter (VACM) on a subsurface mooring and a benthic acoustic stress sensor (BASS) on a bottom tripod are compared to assess their relative accuracy. The instruments were deployed off northern California at a midshelf site (water depth approximately 90 m) as part of the STRESS (Sediment Transport Events on Shelves and Slopes) field program. The subsurface mooring and bottom tripod were within a few hundred meters of each other, with the BASS 5.0 m and the VACM 6.7 m above the bottom, during two tripod deployments of 49 and 32 days in the winter of 1988/89. Speed differences between the VACM and BASS current observations have a mean of 0.2 cm s−1 and a standard deviation...
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Onshore volume transport (Stokes drift) due to surface gravity waves propagating toward the beach can result in a compensating Eulerian offshore flow in the surf zone referred to as undertow. Observed offshore flows indicate that wave-driven undertow extends well offshore of the surf zone, over the inner shelves of Martha’s Vineyard, Massachusetts, and North Carolina. Theoretical estimates of the wave-driven offshore transport from linear wave theory and observed wave characteristics account for 50% or more of the observed offshore transport variance in water depths between 5 and 12 m, and reproduce the observed dependence on wave height and water depth.During weak winds, wave-driven cross-shelf velocity profiles...
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Hudson Shelf Valley is a 20–30 m deep, 5–10 km wide v-shaped submarine valley that extends across the Middle Atlantic Bight continental shelf. The valley provides a conduit for cross-shelf exchange via along-valley currents of 0.5 m s−1 or more. Current profile, pressure, and density observations collected during the winter of 1999–2000 are used to examine the vertical structure and dynamics of the flow. Near-bottom along-valley currents having times scales of a few days are driven by cross-shelf pressure gradients setup by wind stresses, with eastward (westward) winds driving onshore (offshore) flow within the valley. The along-valley momentum balance in the bottom boundary layer is predominantly between the pressure...
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