VARIABILITY OF TIDAL CURRENTS IN A WIDE STRAIT - A COMPARISON BETWEENDRIFTER OBSERVATIONS AND NUMERICAL SIMULATIONS

The spatial variability of semidiurnal tidal currents throughout the w aters of the northwest coast of Canada is investigated by examination of velocities of surface drifters recording half-hourly Loran-C positi ons. Time series are examined to remove any records with significant i nertial currents. The remaining records are segmented into sequential 25-hour blocks, detrended, and analyzed for semidiurnal energy. Tidal current ellipses are computed and compared with two different numerica l models: a finite element barotropic simulation, and a finite differe nce baroclinic simulation that was initialized with horizontally unifo rm density surfaces. Models and observations show the dominance of neg ative rotation (clockwise rotary) with the amplification of currents s horeward of the continental slope. In shallow waters both models agree well with the observations. Along the edge of the continental shelf i n waters deeper than 200 m the baroclinic model provides better agreem ent with observations because of its ability to simulate internal tide s. However, observations also reveal that internal tidal currents at a nd seaward of the shelf break may be irregular because of the presence of plumes and jets, and a baroclinic model with horizontally uniform stratification cannot reproduce local features in these jets and plume s. Internal tidal currents in Dixon Entrance exceed those simulated by the baroclinic model by a significant degree. This is likely due to t he constraints of the density field used to initialize the model and t o terrain smoothing in its 5-km grid.