SPATIAL AND TEMPORAL STRUCTURE OF THE BAROTROPIC RESPONSE OF THE SCOTIAN SHELF AND GULF-OF-MAINE TO SURFACE WIND STRESS - A MODEL-BASED STUDY

The barotropic current and pressure field responses of the Scotian She lf and Gulf of Maine region to spatially uniform wind stress are exami ned using a three-dimensional finite-element numerical model. The mode l is linear and harmonic with spatially varying eddy viscosity and bot tom friction coefficients obtained from a nonlinear M-2 tidal solution . The solutions for low-frequency (20-day period) wind stress and upst ream boundary forcing are generally consistent with previous depth-ave raged model results, showing a substantially stronger response for alo ng-shelf (compared to cross-shelf) stress and strong topographic shapi ng of the associated ''arrested topographic waves.'' With their expand ed domain and dimensionality, the present solutions reveal important a dditional features of the responses, such as the Northeast Channel bei ng the primary conduit for cross-shelf subsurface Row compensating the cross-shelf Ekman transport over the Scotian Shelf, widespread areas of near-bottom upwelling and downwelling along the coast and shelf bre ak, and leakage of the response across the shelf break. Model solution s for stress forcing with periods in the ''storm band'' (2-5 days) sho w similar structures and elevation/current gains to those in the low-f requency solutions, with the primary exception that the large Northeas t Channel transport for along-shelf stress excites a topographic wave over the continental slope south of Georges Bank. The strength of bott om stress, dependent on the magnitudes of both the bottom friction coe fficient and near-bottom viscosity in the model, has a significant qua ntitative influence on the inner-shelf response (coastal elevation amp litudes and cross-shelf decay scales) in particular. The implications of the model solutions for the interpretation of various observational features of the region's response to wind stress are discussed, inclu ding coastal elevations, offshore bottom pressures, currents, transpor ts, upwelling zones, frequency dependences, and seasonal and frictiona l influences.