A three-dimensional model of tide and wind-induced residual currents in the central strait of Georgia, Canada

A 3-dimensional baroclinic numerical model has been used to study residual, i.e. mean and low-frequency (< 0.5 cycles day(-1)), currents of the Strait of Georgia, Canada. In the central part of the Strait, the observed mean circulation is characterized by cyclonic eddies of about 8 km diameter. The observed low-frequency currents account for approximately half of the total kinetic energy of the fluctuating currents; the other half is associated with diurnal and semi-diurnal tidal currents. The low-frequency currents have about one-third of their energy at the fortnightly and monthly bands. The mean and low-frequency fluctuating components have similar amplitudes. The model is forced with tides, winds and runoff and produces energy levels that are smaller than, but comparable to, the observed mean and low-frequency currents. The spatial (e.g. eddy formation) and temporal structures are reasonably reproduced. It is found that the residual currents in the model are produced by non-linear interactions of the diurnal and semi-diurnal tidal components and by wind forcing, thereby supporting earlier suggestions based on observations; about 50% of the variance in the model is contained in frequencies of tidal origin and the rest is spread over a broad energy band, which is related to wind forcing. A qualitatively good agreement between modelled and observed currents is found in the upper and middle parts of the water column. (C) 1996 Academic Press Limited