This project will investigate, using high-resolution, process-oriented numerical simulations, the role of destruction of potential vorticity (PV) by winds in the dynamics of two key elements of the general circulation: separated western boundary currents (SWBCs) and their southern recirculation gyres (SRGs). The physics governing SRGs is intimately tied to eddy PV fluxes and to the processes that create the low-PV mode water that fills the gyres.
Scaling arguments and preliminary numerical experiments suggest that frictional forces associated with winds blowing along the density front of a SWBC can be as effective in forming low PV water, as the classical mechanism involving diabatic processes associated with atmospheric cooling. The preliminary experiments also suggest that eddy PV fluxes at wind-driven fronts scale with the wind-stress through the surface frictional PV flux.
Two model configurations will be used for the proposed numerical experiments. The first will focus on the frontal region of a wind-forced SWBC to characterize the eddy PV fluxes and develop a parameterization for these fluxes based on surface PV fluxes. The other model configuration will consist of a double-wind gyre, with a sloping western boundary. This configuration is designed to study the competing effects of eddy PV fluxes (driven by surface PV fluxes), gyre-scale advective PV fluxes, and frictional PV fluxes in the bottom Ekman layer in determining the PV and circulation of the SRG.
