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

Abstract

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.