The Mesoscale Eddy Field in the Northern North Atlantic and its Relationship to Linear Baroclinic Instability

A 10-year long eddy-permitting ocean simulation is used to form an eddy census for the northern North Atlantic and Arctic Ocean. Coherent vortices are extracted from daily-mean fields by a hybrid detection method that searches for closed surface geostrophic streamilnes and negative Okubo-Weiss values. The method picks up very few eddies in the Arctic Ocean, likely due to the prevalence of sub-surface eddies there or small sizes compared to the model resolution. In contrast, the calculations show that coherent vortices are indeed responsible for the bulk of eddy kinetic energy in the Nordic Seas and the northern extremities of the North Atlantic. Boundary currents, following continental slopes, are the primary sources for most of the eddy field, but eddies are also advected into the deeper basins. The calculations also point to some expected cyclone-anticyclone asymmetries with respect to hydrographic properties and propagation. Linear stability calculations done on the time-mean background model field suggest that baroclinic instability is a consistent source of the eddy field. The calculations also point to important deviations from Eady dynamics and, in particular, suggest that topographic slopes impact unstable growth significantly.