Deep-ocean inertial subrange small bandwidth coherence and Ozmidov-frequency separation

• Published in: Physics of Fluids
• Main Author: van Haren, Hans
• Other Authors: Nederlandse Organisatie voor Wetenschappelijk Onderzoek
• Format: Article in Journal/Newspaper
• Language: English
• Published: AIP Publishing 2019
• Subjects: Condensed Matter Physics; Fluid Flow and Transfer Processes; Mechanics of Materials; Computational Mechanics; Mechanical Engineering; Josephine; Mid-Atlantic Ridge; Northeast Atlantic
• Online Access: http://dx.doi.org/10.1063/1.5099005; https://pubs.aip.org/aip/pof/article-pdf/doi/10.1063/1.5099005/15656105/066603_1_online.pdf

The inertial subrange of turbulence in a density stratified environment is the transition from internal waves to isotropic turbulence, but it is unclear how to interpret its extension to anisotropic “stratified” turbulence. Knowledge about stratified turbulence is relevant for the dispersal of suspended matter in geophysical flows, such as in most of the ocean. For studying internal-wave-induced ocean-turbulence, moored high-resolution temperature (T-)sensors are used. Spectra from observations on episodic quasiconvective internal wave breaking above a steep slope of large seamount Josephine in the Northeast-Atlantic demonstrate an inertial subrange that can be separated in two parts: A large-scale part with relatively coherent portions adjacent to less coherent portions and a small-scale part that is smoothly continuous (to within standard error). The separation is close to the Ozmidov frequency and coincides with the transition from anisotropic/quasideterministic stratified turbulence to isotropic/stochastic inertial convective motions as inferred from a comparison of vertical and horizontal cospectra. These observations contrast with T-sensor observations of shear-dominated internal wave breaking in an equally turbulent environment above the slope of a small Mid-Atlantic ridge-crest, which demonstrate a stochastic inertial subrange throughout.