The Internal Tide off the West Coast of Vancouver Island

Abstract

Using data from the Coastal Ocean Dynamics Experiment (CODE) and the Island Coastal Current Experiment, the internal tide off the west coast of the Vancouver Island was studied. Although the semidiurnal barotropic velocity field in the area was weak, the baroclinic field was found to be relatively strong with speeds up to five times greater. The intermittent nature of the baroclinic field was resolved by estimating the M2 tidal harmonic coefficients every 24 hours in 15-day overlaping intervals. These time-evolving coefficients were then analysed using spectral analysis methods. For most of the area under investigation, the internal tide was generated mainly at the shelf break and was found to propagate cross-shore. Off Estevan point, where the bottom contour is regular, the beam structure was identified and traced to distances 40 km from the generation region on the slope. The downward-propagating beam was found to follow the seasonal variation of the characteristic propagation paths. An empirical orthogonal function analysis revealed a highly coherent baroclinic field (78% of the M2 variance). The predictions of an internal tide model were found to he in good agreement with the experimental results on the slope. The interaction of a cyclonic eddy, present in the area during August 1980, with the internal tide was also addressed.