The efficiency of mixing in turbulent patches: inferences from direct simulations and microstructure observations

We investigate the time evolution of mixing in turbulent overturns, using a combination of direct numerical simu-lations (DNS) and microstructure profiles obtained during two field experiments. Our focus is on the flux coeffi-cient , the ratio of the turbulent buoyancy flux to the tur-bulent kinetic energy dissipation rate . In observational oceanography, a constant value = 0:2 is often used to infer the buoyancy flux and the turbulent diffusivity from measured . In the simulations, the value of changes by more than an order of magnitude over the life of a turbu-lent overturn, suggesting that the use of a constant value for is an oversimplification. To account for the time dependence of in the interpretation of ocean turbulence data, we require a way to assess the evolutionary stage at which a given turbulent event was sampled. The ra-tio of the Ozmidov scale, L O, to the Thorpe scale,