Interactions between near-inertial motion and unstable barotropic jets

It is generally accepted that low Rossby number geostrophic currents evolve independently of background near-inertial motion. Here, we consider a pair of barotropically unstable jets in a thin-aspect-ratio homogeneous fluid. 3D motion is added to the initial conditions in the form of a vertical shear with no horizontal structure. We examine feedbacks between the 3D and 2D modes as a function of the Rossby number. With an eye towards parameterization, we also look for correlations between the Reynolds stress forcing of the 2D flow and various fields derived from Weiss-like stability criteria (of 2D flow to 3D perturbations). We also point out that, in a forced-dissipative scenario, the solution may simply spin up until such time that $O(1)$ Rossby number effects allow for a forward energy cascade and suggest that such a mechanism may be relevant to the ocean.