LES of Stably Stratified Turbulence

Large-eddy simulations (LES) of forced uniformly stably stratified turbu-lence with grid points up to 5123 were performed with the degrees of stratification such that both nonlinear turbulent interactions and internal gravity wave motions play es-sential roles. The degrees of stratification correspond to those of the ocean turbulence at length scale O(10)[m]. It is assumed that at the subgrid scales, the flow is nearly isotropic and that the density fluctuation is approximated by a passive scalar. The LES model equations are derived by using the Lagrangian renormalized approximation which is free from any ad hoc parameter. Energy density of the simulated flow in the wavevector space is strongly anisotropic. The vertical shear spectrum is in qualitative agreement with the measurements in the ocean by Gargett et al.. However, the slope of the spectrum in the simulation (α k-1/3) is shallower than that by the measurement (α k-1).