Internal Tide Observations from the Australian North West Shelf in Summer 1995

Abstract

Observations are presented of the internal tide over the continental shelf and slope from a cross section on the Australian North West Shelf. Data collected from moored instruments and repeated profile measurements during the summer months of 1995 show an energetic, large amplitude, shoreward propagating semidiurnal internal tide. Multiple generation sites are suggested, coinciding with near-critical bottom slopes. In water less than approximately 200 m deep, the vertical structure of the internal tide is predominantly a first vertical mode, whereas in deeper water over the slope the vertical structure is more complicated with currents and vertical displacements intensified in the lower part of the water column. The internal tide is largely confined to a region approximately 100 km wide, from water depths between 70 and 1000 m. Strong generation and dissipation of the internal tide energy is observed over this region and there is evidence that the dissipated energy impacts on the vertical mixing of the density field, particularly near the shelf break and upper continental slope. Even though the diurnal barotropic tidal currents are weak, a diurnal internal tide is observed and appears to be generated over a section of the continental slope that is at the critical slope for the K1 tidal frequency. The M4 harmonic is also observed and this results from nonlinear interactions of the M2 baroclinic tide.