A numerical investigation into the bottom boundary layer flow and vertical structure of internal waves on a continental slope

A numerical investigation is made into the vertical structure and boundary-layer flow of semi diurnal tidal-period internal waves. The Princeton Ocean primitive equation Model, incorporating the Mellor–Yamada level 2.5 turbulence closure scheme, is used to study the flow and turbulence associated with propagating internal waves in a stratified ocean. Effects of stratification, seabed slope and a background barotropic tide are investigated. Of particular interest is the intensification of currents near the seabed that occurs for critical or near-critical slopes when the topographic slope is comparable to the slope of the internal wave characteristics. In the absence of friction, infinite intensification of currents is predicted near the seabed, but realistic bottom friction and vertical eddy viscosity reduce the bottom currents to about twice the speed of the surface currents. Over critical slopes, maximum current shear and vertical eddy viscosity are achieved. Strong asymmetry occurs between upslope and downslope flows. Downslope flows near the seabed are stronger and have thinner boundary layers than the upslope flow. Observations are presented of semi-diurnal internal tides from around the shelf break on the Australian North West Shelf. Bottom intensification of currents and asymmetry between upslope and downslope flows are observed, in qualitative agreement with the model.