The energetics of breaking events in a resonantly forced internal wave field

The energetics of breakng events in a resonantly forced internal wave field was investigated by deriving a series of vertical density profiles in a stratified tank in which a standing internal wave was forced to amplitudes at which it became unstable. As a result of the instability, the internal wave displayed localized patches of mixing within the fluid. By resorting the density profiles, the available potential energy in the patches was calculated, and, by a comparison with the average buoyancy flux in the tank, an average efficiency of utilization of available potential energy was calculated. It is shown that the temperature and the conductivity gradient spectra in different patches can be interpreted in a way consistent with the visualization of mixing events, showing an evolution from the generation of an initially unstable density distribution, through the formation of coherent structures as the fluid restratifies, and finally to the degeneration of these structures into the finer scales of motion at which mixing occurs.