Spatial and temporal structure of the barotropic response of the Scotian Shelf and Gulf of Maine to surface wind stress: A model‐based study

Abstract

The barotropic current and pressure field responses of the Scotian Shelf and Gulf of Maine region to spatially uniform wind stress are examined using a three‐dimensional finite‐element numerical model. The model is linear and harmonic with spatially varying eddy viscosity and bottom friction coefficients obtained from a nonlinear M2 tidal solution. The solutions for low‐frequency (20‐day period) wind stress and upstream boundary forcing are generally consistent with previous depth‐averaged model results, showing a substantially stronger response for along‐shelf (compared to cross‐shelf) stress and strong topographic shaping of the associated “arrested topographic waves.” With their expanded domain and dimensionality, the present solutions reveal important additional features of the responses, such as the Northeast Channel being the primary conduit for cross‐shelf subsurface flow compensating the cross‐shelf Ekman transport over the Scotian Shelf, widespread areas of near‐bottom upwelling and downwelling along the coast and shelf break, and leakage of the response across the shelf break. Model solutions for stress forcing with periods in the “storm band” (2–5 days) show similar structures and elevation/current gains to those in the low‐frequency solutions, with the primary exception that the large Northeast Channel transport for along‐shelf stress excites a topographic wave over the continental slope south of Georges Bank. The strength of bottom stress, dependent on the magnitudes of both the bottom friction coefficient and near‐bottom viscosity in the model, has a significant quantitative influence on the inner‐shelf response (coastal elevation amplitudes 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, including coastal elevations, offshore bottom pressures, currents, transports, upwelling zones, frequency dependences, and seasonal and frictional influences.