Impact of Wind Forcing, Bottom Topography, and Inertia on Midlatitude Jet Separation in a Quasigeostrophic Model

The persistence of unrealistic Gulf Stream separation in numerical models of the ocean has prompted many theories about possible mechanisms that influence the separation of a western boundary current from the coast. In this paper, the joint effects of (a) coastline orientation, (b) bottom topography, and (c) inertia on the midlatitude jet separation are explored in a wind-driven two-layer quasigeostrophic model. It is shown that topographic effects are of importance in high eddy activity regions and that eddy–topography interactions strongly influence the separation process. In order for the western boundary current to separate from the coastline and cross the f/h contours associated with the continental rise, eddy fluctuations need to be weak at the separation point. This can be achieved either by introducing a positive wind stress curl in the northern part of the domain or by increasing the inertia of the western boundary current. In both cases, the separation is facilitated by low eddy activity, resulting in a decoupling of the upper layer from the lower layer when the current crosses the f/h contours.