DNS and LES of inertia-gravity wave breaking

Despite its important role in maintaining the circulation in the middle atmosphere, the breaking of inertia-gravity waves is still not especially well understood, in part because the wide range of scales involved, from the relatively large scale of the wave and the primary instability structures to the turbulent small scales where energy and momentum are dissipated, make well resolved observation and numerical simulation difficult. In this study, we systematically analyse the breaking of both high- and low-frequency monochromatic inertia-gravity waves using a combination of linear stability analysis and direct numerical simulation (DNS).

Normal mode and singular vector analysis is used to determine the dominant scales of instability of statically unstable inertia-gravity waves and then to initialize 3D DNS. In order to make the DNS feasible, Reynolds numbers on the order of 40000, relevant to breaking waves in the upper mesosphere, are used. The DNS are then used as reference data to validate standard large-eddy simulation (LES) schemes, including the implicit Adaptive Local Deconvolution Method (ALDM), wherein the truncation error in the discretization of the governing partial differential equations is tuned so as to function as an implicit sub-gridscale turbulence parameterization.