Subtidal Response of Scotian Shelf Circulation to Local and Remote Forcing. Part II: Barotropic Model

Abstract

A linear, barotropic numerical model that features realistic bathymetry of the Scotian Shelf provides solutions forced by steady and periodic wind stress that are generally incoherent on spatial scales of the shelf width. Closed circulation cells occur in association with, and on the scales of, major bathymetric features. Bathymetrically steered flow is prevalent, and more evident at lower frequencies. Model transport forced by a coastally trapped wave propagating across the backward boundary is not sensitive to the model structure of the incident wave; bathymetry rapidly modifies the wave form as it propagates in the free direction. Higher modes and reflected waves are probably dissipated over short distances by mattering and strong bottom stress. Patterns seen in the model solutions are consistent with results from more fundamental models, and are readily explained by relatively simple vorticity balances. Model results generally reproduce the diverse local and nonlocal velocity responses observed on the Scotian Shelf during winter. The model is more effective in accounting for the remote contribution to circulation. Wind-forced results generally reflect the observed directional variability, and are similar in magnitude to observations inside the 100-m isobath but underestimate the actual current response at deeper stations. It is speculated that spatial variability in wind stress, an effect not addressed in this work, may be responsible for some of this difference. The significant of baroclinic effects in deeper water, which cannot be discounted, is also beyond the scope of this model. Nevertheless, the fairly good agreement between the model and observed current responses to local and nonlocal forcing confirms the importance of bathymetric modifications to Scotian Shelf circulation at subtidal frequencies.