The stability of the Norwegian Atlantic Current east of the Lofoten Basin

The Norwegian Atlantic Current (NwAC) that flows along the Norwegian continental slope is characterized by sharp property fronts that delineate coastal waters from open oceanic waters. A rich mesoscale eddy field along this current suggests that it is hydro-dynamically unstable. The eddy activity is most intense along a very steep portion of the continental slope off the Lofoten-Vesterålen islands, east of the Lofoten Basin (LB). We investigate the stability of the NwAC in this region by performing linear stability calculations on time-mean fields from an 800m-resolution numerical model run. The primary goal is to ascertain whether barotropic or baroclinic instability (or a mix of the two) is primarily responsible for the high eddy kinetic energy levels. We investigate the effect of complex and steep topography by conducting one-layer and two-layer Rotating Shallow Water (RSW) stability calculations. The study area is divided into several sub-zones based on the topographic features and peculiarities. The calculations reveal that baroclinic instability of the boundary current is likely the primary source of the mesoscale variability observed in this part of the Nordic Seas. However, horizontal shear instability also contributes considerably in some regions where the topographic slope is particularly large.