SEASONAL-VARIATION OF THE 3-DIMENSIONAL MEAN CIRCULATION OVER THE SCOTIAN SHELF

The seasonal-mean circulation over the Scotian Shelf is studied numeri cally by computing mean and tidal current fields for winter, spring, a nd summer using a three-dimensional nonlinear diagnostic model. The me an current fields are forced by seasonal-mean baroclinic pressure grad ients, tidal rectification, uniform wind stresses, and associated baro tropic pressure gradients. A historical hydrographic database is used to determine the climatological mean baroclinic forcing. Upstream open boundary conditions are estimated from the density fields to give no normal geostrophic bottom flow and are specified as either along-bound ary elevation gradients or depth-integrated normal velocities. The num erical solutions for nominal bimonthly periods (January-February, Apri l-May, and July-August) reveal the dominant southwestward nearshore an d shelf-break flows of relatively cool and fresh shelf water from the Gulf of St. Lawrence and Newfoundland Shelf, with speeds up to about 2 0 cm/s. The seasonal intensification of the southwestward flows is rep roduced by the model, with the transport increasing from 0.3 Sv in sum mer to 0.9 Sv in winter on the Inner Halifax section. There are also p ronounced topographic-scale influences of submarine banks, basins, and cross-shelf channels on the circulation; such as anticyclonic gyres o ver banks and cyclonic gyres over basins. Baroclinicity is the dominan t forcing throughout the domain, but tidal rectification is comparable on the southwestern Scotian Shelf (e.g., about 0.2 Sv recirculating t ransport around Browns Bank for all the periods). The mean wind stress generates offshore surface drift in winter. The solutions are in appr oximate agreement with observed currents and transports over the Scoti an Shelf, although there are local discrepancies.