Energetic Submesoscales Maintain Strong Mixed Layer Stratification during an Autumn Storm

06 Nov 2017

Atmospheric storms are an important driver of changes in upper-ocean stratification and small-scale (1-100 m) turbulence. Yet, the modifying effects of submesoscale (0.1-10 km) motions in the ocean mixed layer on stratification and small-scale turbulence during a storm are not well understood. Here, we use large-eddy simulations to study the coupled response of submesocales and small-scale turbulence to the passage of an idealized autumn storm, with a wind stress representative of a storm observed in the North Atlantic above the Porcupine Abyssal Plain. Due to a relatively shallow mixed layer and a strong down-front wind, existing scaling theory predicts that submesoscales should be unable to re-stratify the mixed layer during the storm. In contrast, our simulations reveal a persistent and strong mean stratification in the mixed layer both during and after the storm. In addition, we find that the mean dissipation rate remains elevated throughout the mixed layer during the storm, despite the strong mean stratification. These results are attributed to strong spatial variability in stratification and small-scale turbulence at the submesoscale and have important implications for sampling and modeling submesoscales and their effects on stratification and turbulence in the upper-ocean.