Numerical models of the general circulation in the Strait of Georgia

Numerical models have been used to study the low frequency (< 0.5 cycles per day) currents of the Strait of Georgia. In the central part of the Strait, the observed mean (i.e., time-averaged) residual circulation is characterized by cyclonic eddies in the velocity field of about eight kilometers in 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 semidiurnal tidal currents. These low frequency currents have about one-third of their energy at the fortnightly and monthly bands. The magnitudes of the mean and low frequency fluctuating components are about the same. Two different models are used in this thesis to study these currents. The first is a depth-independent numerical model. The model reproduces the location and scale of the observed depth-averaged mean residual but significantly underestimates the magnitude of the velocity. The model low frequency oscillations are basically confined to the fortnightly band and once again the magnitude of the velocity is significantly underestimated. The second is a three-dimensional baroclinic model. This model has energy levels that are comparable to those of the observed mean residual and low frequency components. The spatial and temporal structure are now reasonably reproduced especially for the fluctuating component. Bearing in mind the limitations of the models in reproducing the observed residual (particularly the depth-averaged model) various diagnostic analyses have been performed with the aim of revealing the mechanism(s) maintaining the observed residual. It has been found that no matter where the energy comes from (e.g., baroclinic forcing, wind or tides) the non-linear interactions transfer energy to the low frequency bands. Deep-water renewal in the Strait of Georgia has been successfully modeled. Renewal occurs in the model, during summer, once a month. The phase and amplitude of renewal events compare well with those observed in the central Strait of Georgia. A deep water renewal event starts at extreme neap tides, the time of minimal mixing, when maximum stratification is reached at Boundary Passage and the denser waters of Juan de Fuca Strait penetrate past the sill at Boundary Passage and reach the bottom of the deep basin in the central Strait of Georgia as a gravity current.Science, Faculty ofEarth, Ocean and Atmospheric Sciences, Department ofGraduat