We describe results from some idealized numerical calculations in which we examine the influence of a barotropically stable mean flow on wind-driven variability in a flat-bottomed barotropic vorticity equation model. The mean flow has features in common with the vertically integrated time-mean circulation found in eddy-resolving models with a Sverdrup interior, western boundary current and inertial recirculation region. We integrate the equations of motion linearized about this flow and driven by oscillating wind forcing and compare the results with those obtained when the mean state is one of rest. We find that the presence of a mean flow leads to significant distortion of the model response particularly near the western boundary and in the inertial recirculation region. This distortion is characterized by downstream amplification and phase lag compared to the rest mean state cases. It is related, on the one hand, to the distortion of the mean potential vorticity contours from lines of latitude and, on the other, to advection by the mean flow. Possible applications of these results are discussed to explain features of observed variability in the Gulf Stream system and also the anomalous southward intrusion of the Oyashio Current along the coast of Japan.
Greatbatch, Richard J., and Jin Li. 1990. "Barotropic variability in the presence of an ocean gyre." Journal of Marine Research 48, (1). https://elischolar.library.yale.edu/journal_of_marine_research/1960