Submesoscale and boundary layer turbulence under mesoscale strain

The interaction among quasi-geostrophic mesoscale eddies, submesoscale fronts, and boundary-layer turbulence is a central problem in upper ocean dynamics. We investigate these multiscale dynamics using a novel large-eddy simulation on a 100km-scale domain with meter-scale resolution. The simulation resolves boundary-layer turbulence at a front subject to wind and convective forcing while it evolves within a prescribed, spatially inhomogeneous mesoscale eddy field. Using a triple flow decomposition, we analyze the kinetic energy pathways between the prescribed mesoscale field, the coherent submesoscale response, and the resolved turbulence. The simulation reveals significant along-front heterogeneity in the structure and intensity of the boundary-layer turbulence. Turbulent kinetic energy and production rates vary by more than an order of magnitude along the front, creating distinct turbulent `hotspots' and `deserts' whose locations are tied to the underlying large-scale flow. These results provide a direct numerical characterization of turbulence modulation by a non-uniform strain field, offering crucial insights for developing more physically robust subgrid-scale parameterizations for next-generation climate models.