Idealized Study on the Effect of Bottom Topography on the Seasonality of the Stability of the Iceland–Faeroe Front

Abstract

AbstractWe investigate the effects of bottom topography on the instability, eddy-driven heat flux, and overturning of a front that sits atop a ridge by varying the initial location of an idealized frontal outcrop with respect to a topographic ridge. The front is periodic in the along-ridge direction and unstable to both mixed layer and mesoscale baroclinic instabilities with both instabilities focused on the northern flank of the ridge where the front outcrops. We find agreement with the theoretical predictions for the development of mesoscale instability of the jet in the presence of sloping bottom topography, and we find the initial growth of surface mixed layer eddies is insensitive to topographic variations. However, during the finite amplitude phase of mixed layer instability, we find faster development of mesoscale eddies and thus a stronger cross-front eddy heat flux and residual circulation for the position of the jet where we found the faster growth of mesoscale baroclinic instability. Over an advective time scale that represents the transit time of a water parcel along the Iceland–Faeroe Ridge (IFR), the resulting eddy heat flux is greatest in the cases where the frontal jet experiences the most destabilizing bottom topography of the three cases tested, with values comparable to the heat flux associated with the mean flow. Therefore, eddy dynamics over the IFR frontal region are important contributors to the heat exchanges between the North Atlantic and Nordic Seas, with the bottom topography playing a key role in determining the largest heat fluxes, whether the initial growth is dominated by mixed layer eddies or mesoscale eddies.