Turbulence and Thermal Structure in the Upper Ocean: Turbulence-Resolving Simulations

The upper layer of the ocean participates directly in the exchange of momentum, heat and moisture with the atmosphere. We consider three examples of upper-ocean flow and heat transfer in the present contribution. These examples range from the canonical problem of a stratified shear layer to the surface boundary layer driven by wind and a diurnally varying heat flux to deep cycle turbulence in the Equatorial UnderCurrents (EUC). These problems illustrate stratified shear flow turbulence, wind-driven entrainment in a stratified, rotating fluid, and the communication of surface forcing to subsurface currents in the upper ocean. We discuss the three cases by including new simulations as well as some of our previous work. Direct numerical simulation (DNS) is our tool for the canonical shear layer and, for the other problems, our tool is large eddy simulation (LES) which is increasingly being used to examine turbulent transport and mixing in the ocean. We discuss how buoyancy and rotation affects the spatial structure and temporal evolution of turbulent fluxes, and thereby the distribution of surface inputs of momentum and heat in the upper ocean.