A regional model of the semidiurnal internal tide on the Australian North West Shelf

A fully three-dimensional nonlinear primitive equation model is applied to a study of the semidiurnal internal tide on the Australian North West Shelf, a region of strong barotropic and baroclinic tide. The model shows a significant internal tide over most of the continental slope region, predominantly between 100- and 1000-m depths. Energy flux is highly variable with regions of onshore flux and regions of offshore flux, corresponding to regions of subcritical and supercritical seabed slopes. A comparison between the model and detailed observations from one region shows reasonable agreement in vertical displacement, currents, and depth-integrated energy flux. The comparison also highlights the difficulty in obtaining appropriate observations to provide a rigorous verification of internal tide models. The M-2 and S-2 internal tides show similar patterns of flow with energy in the S-2 internal tide about 25% of that in the M-2 constituent. Estimates of the total baroclinic M-2 energy are about 2.2 GW for the North West Shelf, nearly an order of magnitude larger than suggested by earlier studies. This represents about 5% of the dissipation of the M-2 barotropic tide in the model domain. The seasonal variability in the baroclinic energy flux is about 20% from the mean. The baroclinic energy extracted from the tide is expected to make a significant contribution to mixing in the region.