Formation and arrest of a surface density front via strain-driven frontogenesis

We describe a large-eddy simulation of mixed layer frontogenesis driven by a balanced background flow. The simulation captures the onset of a submesoscale regime from a larger-scale, rotation-dominated front. Frontogenesis shifts the balance between vertical mixing and restratification driven by the frontal ageostrophic secondary circulation and instability. The transition to this state is marked by the appearance of down-front symmetric cells throughout the front, which coalesce to form a circulation that entrains fluid from the base of the mixed layer. We interpret the results in the context of submesoscale instability and potential vorticity transport and discuss relationships with observation and implications for submesoscale frontogenesis.