A Coupled Hydrodynamic–Bottom Boundary Layer Model of Ekman Flow on Stratified Continental Shelves

This paper describes a hydrodynamic model with turbulent energy closure that uses a simplified wave-current interaction model of the bottom boundary layer to compute bed drag coefficients. The coupled model is used to investigate the interaction of the upper and lower boundary layers with the geostrophic core flow for simple shelf geometry and forcing, and to evaluate the effects of increased bottom friction on coastal hydrodynamics for summer and winter stratification. The thickness of the bottom boundary layer predicted by the model ranges from 10 to 35 m and is consistent with observations from the California shelf. The increased bottom friction calculated by the coupled model in intermediate water depths increases bottom Ekman veering (leftward in the Northern Hemisphere) by as much as 10-degrees if stratification is strong, thus enhancing downwelling and upwelling. Currents along isobaths in shallow water are uniformly decreased by as much as 25% in the coupled model for both summer and winter initial stratification.