Potential Vorticity Dynamics of Boundary Currents in a Quasi-geostrophic Ocean

Abstract

Boundary layer potential vorticity dynamics for a quasi-geostrophic, eddy-resolving general circulation ocean model are studied using both Lagrangian and Eulerian analyses. Active western boundary layers are found not only in the upper wind-driven layer but also in the lower layers, despite the lack of a direct vorticity input to the deep ocean. At the western wall dissipative and inertial boundary regimes are exclusively controlled by the time-mean dynamics except for the deepest layer where eddy fluxes drive the mean flow across mean potential vorticity contours. Boundary layers formed at the southern wall in this model are dynamically distinct from the western boundary layers; they are controlled solely by the eddy flux of potential vorticity found in this region of active baroclinic instability. Basin-integrated vorticity balances reveal a strong contribution to the vorticity cycle by the lateral boundaries with such input overshadowed by the vorticity exchange across the midbasin gyre boundary in the surface layer.