Equilibration of a warm pumped lens on a β plane

Abstract

The dynamics of a warm lens created by a surface buoyancy flux and Ekman pumping in an initially homogeneous, unbounded fluid on a β plane is studied in a set of high-resolution numerical experiments. A simple analytical model for the equilibrium structure of the lens is developed that assumes that the input of vorticity and buoyancy from the Ekman layer is balanced through transfer by baroclinic eddies that carry the warm fluid laterally away from the lens. The importance of eddy-induced diapycnal flux in the western intensification region is emphasized by developing a boundary layer theory based entirely on the cross-frontal mass exchange due to eddies. The theory is successfully tested against direct numerical eddy-resolving simulations. Possible oceanographic implications of the study for understanding subtropical gyres and the Antarctic Circumpolar Current are discussed.