Large-aspect-ratio structures in simulated ocean surface boundary layer turbulence under a hurricane

The LES captures the observed deepening, cooling, and persistent stratification of the OSBL as the storm approaches and passes. As the storm approaches, surface-intensified Ekman-layer rolls, with horizontal wavelengths of about 200m and horizontal-to-vertical aspect and velocity magnitude ratios of about 20, dominate the kinetic energy and increase the turbulent Prandtl number from about 1 to 1.5 due partially to their restratifying vertical buoyancy flux.

However, as the storm passes, these rolls are washed away in a few hours due to the rapid rotation of the wind. In the bulk OSBL, the gradient Richardson number of the mean profiles remains just above (just below) 1/4 as the storm approaches (passes). At the base of the OSBL, large-aspect-ratio Kelvin-Helmholtz billows, with Prandtl number below 1, intermittently dominate the kinetic energy.