Vertical mixing in homogeneous sheared stratified turbulence: A one-dimensional-turbulence study

We conduct a parametric study of diapycnal mixing using one-dimensional-turbulence (ODT) simulations. Homogeneous sheared stratified turbulence is considered. ODT simulations reproduce the intermediate and energetic regimes of mixing, in agreement with previous work, but do not capture important physics of the diffusive regime. ODT indicates K-rho similar to epsilon/N-2 for the intermediate regime, and K-rho similar to (epsilon h(4))(1/3) for the energetic regime and limit of near-zero stratification. Here K-rho is the turbulent diffusivity for mass, e the dissipation rate, N the buoyancy frequency, and h the computational domain height, where h is relevant mainly in simulations with jump-periodic vertical boundary conditions. These scaling relationships suggest that K-rho is independent of the molecular diffusivity. ODT results for a wide range of parameters show that K-rho cannot be parametrized solely with the turbulent intensity parameter epsilon/(vN(2)), in contrast with the previous studies, but it is well predicted by correlations using the Ellison length scale. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3592329]