A NUMERICAL-MODEL OF INTERNAL TIDES WITH APPLICATION TO THE AUSTRALIAN NORTH-WEST SHELF

A nonlinear, primitive equation, finite-difference numerical model is applied to the problem of the generation, propagation, and dissipation of internal tides over a cross section of the continental slope and s helf topography of a region on the Australian North West Shelf. The mo del is forced through the specification of the offshore tidal elevatio n and as such the full tidal field is modeled for the M(2) constituent . An energetic internal tide is produced in the model with results sho wing sensitivity to changes in both stratification and bathymetry. The ratio of the slope of the internal wave characteristics to the bathym etry is generally less than or close to one, producing subcritical and approximately critical conditions. Model results are compared to prev iously reported observations and show reasonable agreement in terms of wave structure, propagation direction, and regions of generation and energy dissipation. The model shows a high degree of spatial variabili ty in the amplitude and phase of internal wave currents and vertical d isplacements with motion tending to propagate along characteristic pat hs as beams of signal. However, dissipation prevents the beams from ra diating large distances from the generation regions. The energy flux o f the internal tide propagates both onshore and offshore and the magni tude of the flux is strongly dependent on the slope of the bathymetry with largest values occurring for steepest topography. The internal wa ve amplitude and hence energy flux is also found to be dependent on th e magnitude of the vertical and horizontal mixing of momentum with max imum values achieved under conditions of no mixing.