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

Abstract

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 M2 and S2 internal tides show similar patterns of flow with energy in the S2 internal tide about 25% of that in the M2 constituent. Estimates of the total baroclinic M2 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 M2 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.