Theories of Internal Wave Interaction and Stably Stratified Turbulence: Testing Against Direct Numerical Experimentation

Abstract

Direct numerical experiments, both in 2D (vertical plane) and in 3D geometries, reveal the roles of nonlinear energy transfer and of vertical buoyancy (heat) flux in governing the wavenumber spectra of stably stratified turbulence. Buoyancy flux is typically negative (downwards) at large scales and positive (upwards, “restratifying”) at small scales where “small scale” may include the overturning scale. Numerical experiments provide a basis for testing some aspects of theoretical research. A practical concern arises because energy spectra and dissipation rates do not clearly imply the magnitude nor even the sign of the overall buoyancy flux.