Waves explain observed similarity scaling of turbulence dissipation in the Southern Ocean

Abstract

Abstract We investigate the turbulence kinetic energy (TKE) budget of the upper ocean and its response to wind and wave forcing in the Southern Ocean, using realistically forced Large Eddy Simulations (LES) and in situ microstructure shear observations. The widely used law-of-the-wall similarity scaling assumes that shear production of TKE is balanced by its dissipation. However, our findings reiterate that this assumption is violated under wave forcing: dissipation is primarily balanced by local Stokes shear production, augmented by almost equal contributions from local Eulerian shear production and non-local convergence of TKE transport. Despite this, the canonical law-of-the-wall scaling reasonably describes the vertical distribution of dissipation rates in the boundary layer in both realistically-forced LES and observations, even though the underlying physical reasoning does not hold. We propose a modified scaling to account for the non-local component of the TKE budget that yields accurate predictions of the TKE budget as well as an interpretation accounting for wave effects. These insights have important implications for interpreting turbulence dissipation rate observations.