Continental shelf waves of diurnal period along Vancouver Island

Abstract

Recent surveys of tides and currents on the continental shelf along the west coast of Vancouver Island have shown the diurnal tidal currents to be larger than the semi‐diurnal by a factor of 2–4, although the ratio (K1 + O1)/(M2 + S2) for the tidal heights is only 0.6. We attribute the diurnal currents to continental shelf waves, and show that the continental shelf and slope off Vancouver Island allow first mode barotropic shelf waves at the diurnal frequency. The tidal heights and deep water currents of K1 and O1 frequency behave as progressive Kelvin waves with height 43 cm at shore, and currents of 1–2 cm/s. The observed shelf waves at these frequencies have amplitudes at shore of 5 and 3 cm, and currents of order 10 and 6 cm/s, respectively. The Kelvin and shelf waves are in phase near Ucluelet and out of phase near Kyuquot, as determined by both current meter and shore tide gauge observations. Observed wavelengths are longer than predicted for a barotropic shelf wave, in accordance with the expected influence of stratification.