Shelf Cross-Shore Flows under Storm-Driven Conditions: Role of Stratification, Shoreline Orientation, and Bathymetry

Numerical simulations are used to study the response of Long Bay, South Carolina, a typical coastal embayment with curved coastline located on the South Atlantic Bight, to realistic, climatologically defined, synoptic storm forcing. Synoptic storms, consisting of cold and warm fronts as well as tropical storms, are used as forcing under both mixed and stratified initial conditions. The analysis focuses on the development of cross-shore shelf circulation and the relative contributions of regionally defined cross-shore winds and alongshore bathymetric variation. The simulation results show that, under stratified conditions, the regionally defined offshore-directed wind component promotes upwelling during the developing stage of the cold front and enhances mixing during the decaying stage. No significant effect is found for warm front and tropical storm forcing conditions. Net cross-shore transports are induced at the southern and northern sides of the embayment that have opposing signs. Besides the surface and bottom Ekman transports, geostrophic transport due to alongshore shelf bed slope and horizontal advection are found to be important contributors to cross-shore flow development. Sea level variability along the curved coastline is driven by the regional alongshore wind, but a spatial variability is identified from the locally defined components of along- and cross-shore winds controlled by coastline orientation.