Equilibration of Symmetric Instability and Inertial Oscillations at a Finite-Width Submesoscale Front
Here, we consider the problem of an initially balanced front with a horizontal buoyancy gradient of finite width and bounded by flat no-stress horizontal surfaces. We study the evolution to equilibration of this symmetrically-unstable front using a linear stability analysis and three-dimensional nonlinear numerical simulations. We find drastically different behaviour emerging at late times depending on the strength and width of the front. While weak fronts develop frontlets and excite subinertial oscillations, stronger fronts produce bore-like gravity currents that propagate along the top and bottom boundaries. Although the instantaneous turbulent dissipation rate can be much larger in these strong fronts, the turbulence is intermittent and peaks during periods of weak stratification. We explain the energetics as the front evolves towards the final adjusted state in terms of the dimensionless front strength and aspect ratio.