Instability observations associated with wave breaking in the stable-stratified deep-ocean

High-resolution temperature observations above underwater topography in the deep, stably stratified ocean have revealed two distinctive turbulence processes. These processes are associated with different phases of a large-scale (here tidal) internal gravity wave: (i) highly nonlinear turbulent bores during the upslope propagating phase, and (ii) Kelvin-Helmholtz billows, at some distance above the slope, during the downslope phase. Whilst the former may be associated in part with convective turbulent overturning following Rayleigh-Taylor instabilities 'RTi', the latter is mainly related to shear-induced Kelvin-Helmholtz instabilities. In this paper, details are particularly presented of rare (convective) RTi penetrating stable density stratification under high-frequency internal waves. Such 'apparent RTi' can be explained using both stability parameterization of entrainment across a density interface, and, more relevant here, internal wave acceleration overcoming the reduced gravity.