ACOUSTIC DOPPLER CURRENT PROFILER MEASUREMENTS OF THE SEMI-DIURNAL INTERNAL TIDE ON THE WEST-COAST OF NEW-ZEALAND

Current measurements made by an Acoustic Doppler Current Profiler detail the vertical structure of the internal tide for a site at the continental shelf break on the west coast of New Zealand. The measurements, made over 10 h in late winter, had an 8 m vertical resolution. Tidal analysis of the velocity data shows a 60-degrees change in tidal phase and a 90-degrees change in tide ellipse orientation across the base of the mixed layer. The profiles of tidal ellipse parameters are shown to be consistent with the sum of a barotropic tide and an internal tide in a two density-layer ocean. The barotropic tidal amplitude was 10 cm s-1 whereas the internal tide had a 6.3 cm s-1 amplitude. Both the barotropic and internal modes propagate in a direction approximately normal to the topography.