Along-Slope Current Generation by Obliquely Incident Internal Waves

Numerical studies of internal wave reflection from sloping boundaries are presented. Previous work (Slinn and Riley, 1996, 1998a, 1998b, 1999) has restricted attention to internal waves that approach the bottom slope in a plane normal to the boundary (normal incidence). This work extends the scope of the three-dimensional time-dependent numerical experiments to examine internal waves that approach the slope at an oblique angle φ out of the plane normal to the boundary. These preliminary studies with obliquely incident waves at the critical frequency have shown that strong alongslope mean currents are generated near the boundary by the flux of incident wave momentum when wave breakdown occurs in a turbulent layer above the slope. After a short time the mean boundary currents interact with the oncoming wave field in a complex fashion. The waves break down near the upper interface of the current and no longer penetrate to the slope. Turbulent mixing near the boundary is nearly extinguished, and a new turbulent layer is produced at the upper interface of the shear layer. At this point the flux of wave momentum into the water column occurs farther from the wall, and the net result is a steady thickening of the alongslope boundary current. For the moderate wave parameters used in an illustrative example, within ten wave periods after the onset of wave breaking the mean current is approximately two vertical wavelengths thick and has a velocity close to the phase speed of the oncoming waves in the alongslope direction.