Application of a model of internal hydraulic jumps

Abstract

A model devised by Thorpe & Li (J. Fluid Mech., vol. 758, 2014, pp. 94–120) that predicts the conditions in which stationary turbulent hydraulic jumps can occur in the flow of a continuously stratified layer over a horizontal rigid bottom is applied to, and its results compared with, observations made at several locations in the ocean. The model identifies two positions in the Samoan Passage at which hydraulic jumps should occur and where changes in the structure of the flow are indeed observed. The model predicts the amplitude of changes and the observed mode 2 form of the transitions. The predicted dissipation of turbulent kinetic energy is also consistent with observations. One location provides a particularly well-defined example of a persistent hydraulic jump. It takes the form of a 390 m thick and 3.7 km long mixing layer with frequent density inversions separated from the seabed by some 200 m of relatively rapidly moving dense water, thus revealing the previously unknown structure of an internal hydraulic jump in the deep ocean. Predictions in the Red Sea Outflow in the Gulf of Aden are relatively uncertain. Available data, and the model predictions, do not provide strong support for the existence of hydraulic jumps. In the Mediterranean Outflow, however, both model and data indicate the presence of a hydraulic jump.

Off-bottom turbulence expansions of unbounded flow over a deep-ocean ridge

“…Small vortices asymmetrically distributed above and below may be the cause of the slightly forward tilt of the entire expansion with the upper overturn passing the Tsensor array earlier than the lower overturn. This is also observable in the oval shape in Thorpe et al (2018), but more explicit in the present details.…”

“…The shape of the local mode-2 turbulence expansion at about 200 m above the seafloor is mushroom-or medusalike, but not oval as suggested by Thorpe et al (2018). The expansion thus resembles a horizontal dipolar vortex.…”

“…The upper isotherms (around z ¼ À2000 m, day 183.7) steeply rebound upward while the lower isotherms continue descent (between À2050 < z < À2100 m). This happens when the flow becomes supercritical, following Thorpe et al (2018), here at day 183.70. The shape of the transition to turbulence expansion between days 183.71 and 183.72 resembles a mushroom or perhaps a medusa, on its side, but not an oval as in Thorpe et al (2018).…”

“…This happens when the flow becomes supercritical, following Thorpe et al (2018), here at day 183.70. The shape of the transition to turbulence expansion between days 183.71 and 183.72 resembles a mushroom or perhaps a medusa, on its side, but not an oval as in Thorpe et al (2018). Its more or less vertical front around day 183.71 seems to consist of a vortex pair (see arrows in Fig.…”

“…Musgrave et al, 2016;Thorpe et al, 2018). The shape of the hydraulic transition was characterized as 'oval' and 'mode-2' by a model of Thorpe et al (2018), more or less fitting limited profiling observations in a deep-ocean through-flow.…”