Gulf Stream Slope Eddies and their Submesocale Interior

Wednesday, 17 December 2014
Jonathan Gula, Maarten J Molemaker and James C McWilliams, University of California Los Angeles, Los Angeles, CA, United States
Slope eddies are commonly observed and understood as the product of an instability of the Gulf Stream along the U.S. seaboard. Here we address the finite-amplitude behavior of a slope eddy after formation as a cut-off meander over the Charleston Bump, including its structure, propagation, and emergent submesoscale interior and neighboring substructure, as simulated in very high resolution simulations (dx=150m) of the Gulf Stream along the U.S. seaboard. A very rich submesoscale structure is revealed inside the slope eddy. Meander-induced frontogenesis sharpens the gradients and triggers submesoscale barotropic shear instability on the rim of the eddy. The small scale meandering perturbations become rolled up vortices which are advected back in the interior of the slope eddy. The slope eddy also locally creates a strong southward flow against the shelf leading to boundary generation of centrifugal instability. To illustrate and quantify the impact of a slope eddy in trapping material, generating cross-shelf exchanges and in mixing tracer properties, virtual Lagrangian particles are deployed in the model solutions. We discuss in particular diabatic mixing by the submesoscale processes.