Inner Shelf Circulation Patterns and Nearshore Flow Reversal Under Downwelling and Stratified Conditions off a Curved Coastline

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The role of a curved coastline and associated bathymetry in the development of downwelling circulation in a stratified inner shelf is examined through a number of numerical experiments. Different scenarios include constant versus variable wind-forcing and variations in bottom friction. The three-dimensional response of the shelf within the domain (embayment enclosed by capes) is associated with the generation of a velocity/ pycnocline disturbance at the upstream cape and its subsequent downstream advection. This disturbance is more pronounced under variable wind conditions. Its downstream advection through the bay exhibits different patterns depending on the competition between inertia and bottom friction near the cape. When inertia dominates, the disturbance separates from the cape and travels downwind with an enhanced downstream flow offshore and a countercurrent inshore. The separation occurs at a low Rossby number (Ro ~ 0.15), which is attributed to the positive curvature of the coastline forming the cape. When friction dominates, the advection path is constrained along the coastline, resulting in an alongshore temperature gradient and a transient thermal front running almost perpendicular to the coast/isobaths. Simulations with spatially variable bottom friction, with higher friction toward the coast, result in the generation of eddy-like features. The numerical results are in agreement with both observations and surface temperature imagery from Long Bay, South Carolina, an embayment enclosed by two capes, and emphasize the role that coastline and associated shelf morphology can play in enhancing cross-shelf transport and exchange.

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