Parametric subharmonic instability of inertial shear at ocean fronts

The two-dimensional stability of vertically sheared inertial oscillations at ocean fronts is explored through a linear analysis and nonlinear simulations. Baroclinic effects reduce the minimum frequency inertia-gravity waves to an extent determined by balanced Richardson number ${{Ri}}$ front. Below critical value , which depends on strength shear, become unstable parametric subharmonic instability (PSI) resulting in growing perturbations that oscillate half $f$ . Since always greater than 1, PSI can occur stable symmetric instability. Although modest weak growth rates exceeding $f/2$ be achieved for shear or equal thermal wind shear. Our formulation allows non-hydrostatic applied initially unstratified geostrophic adjustment problems. We find will almost totally damp transient arise during adjustment. gain energy expense ageostrophic production. then themselves secondary Kelvin–Helmholtz instabilities creating pathway dissipated rapidly. In contrast baroclinic draw front's kinetic potential energy, acts increase stored front as convergence divergence eddy-momentum fluxes set up circulation sense stand