Modeling the Effect of Wave–Current Interaction on the Three-Dimensional Wind-Driven Circulation of the Eastern Irish Sea

A high-resolution (0.5′ north–south by 1.0′ west–east) three-dimensional hydrodynamic model of the eastern Irish Sea is used to examine the influence of enhanced bed friction due to wind–wave effects upon the three-dimensional, wind-induced circulation of the eastern Irish Sea. The model uses a mixed finite difference-modal approach, in which a standard finite-difference grid is employed in the horizontal, with the Galerkin method, with an expansion of functions (modes) in the vertical, giving a continuous current profile from sea surface to seabed. Vertical eddy viscosity within the model is a function of the flow field. The model is used to examine the wind-induced response of the area to spatially uniform and constant in time northerly and westerly wind stresses of 1 N m−2. The effect upon bed stresses, and hence the three-dimensional circulation of the region of enhanced bed turbulence due to wind wave effects, is also considered using idealized wave fields. Changes in bed stress, particularly in shallow water regions, have a significant influence upon the wind-induced circulation, especially the wind-induced, near-bed currents. In addition to calculations using a uniform drag coefficient and bed type, the wind-induced circulation using a range of bed types corresponding to the bed composition, from mud to gravel, of the eastern Irish Sea is also considered. The intensity of near-bed turbulence, and hence drag coefficient, due to wave–current interaction is found to vary significantly with bed type, and this also influences the near-bed currents.