On the impact of turbulent mixing on frontogenesis in the surface mixed layer

Arooba Nawaz1, Lars Czeschel2
1Helmholtz-Zentrum Hereon, University of Hamburg
2University of Hamburg

Frontogenesis, a fluid dynamics process, rapidly sharpens horizontal density gradients as a natural consequence of baroclinic instability in the ocean. This sharpening of gradients, in turn, gives submesoscales their characteristic strong vertical velocities and buoyancy flux through ageostrophic secondary circulation by triggering submesoscale instabilities. Our goal is to understand the impact of small-scale turbulence during active submesoscale frontogenesis and the associated energy pathways. For this, we are using Large Eddy Simulation (LES) – in an idealized setup of baroclinically unstable fronts in a weakly stratified mixed layer above a well-stratified interior. To explore the role of turbulence, we vary the resolution up to a computational grid of (O) 1m and apply different sub-grid scale closures. We observed that the turbulence is shaping the ageostrophic cross-frontal circulations, and we discuss the impact on vertical buoyancy and potential vorticity fluxes, i.e. on the restratification of the mixed layer.