Energy Flux to a Cyclonic Eddy off Cabo Frio, Brazil

Abstract

To evaluate the energy flux from the mean flow of South Atlantic western boundary currents toward typical Cabo Frio eddies (at Brazilian southeast coast), the southwestern Atlantic circulation was simulated with the Princeton Ocean Model. Throughout the study period, the vertical profile of eddy available potential energy direction was monitored. The results indicated that baroclinic instability eddies first appear in intermediate depths and then its signal propagates upward, draining energy from the Brazil Current (BC), until it reaches the surface, 30 days after its formation. The depth of eddy formation is related to the vertical profile of the mean potential vorticity cross-current gradient (?q/?s). The beginning of the potential energy flux toward the perturbation and the origin of the eddy occurred at a similar depth and time. The observed pattern suggests the following cycle: 1) a well-defined southwestward-flowing BC in the beginning of the period, with a baroclinically unstable profile of ?q/?s; 2) energy flux from the mean flow toward perturbation at intermediate depth; 3) current destabilization and meandering; 4) formation and growth of the cyclonic eddy; 5) potential energy flux progressively shallower; 6) propagation of the eddy signal upward; and 7) stabilization of the water column.