Turbulence generation by large-scale extreme vertical drafts and the modulation of local energy dissipation in stably stratified geophysical flows

TL;DR

This study uses direct numerical simulations to show that large-scale vertical drafts in stratified flows generate turbulence and significantly influence local energy dissipation, explaining variability observed in oceanic flows.

Contribution

It reveals the role of extreme vertical drafts in turbulence generation and energy dissipation modulation in stratified geophysical flows, a novel insight into oceanic turbulence dynamics.

Findings

Vertical drafts produce intermittent turbulence.

Extreme drafts can account for up to 50% of energy dissipation.

Approximately 10% of the domain flow causes significant dissipation.

Abstract

We observe the emergence of strong vertical drafts in direct numerical simulations of the Boussinesq equations in a range of parameters of geophysical interest. These structures, which appear intermittently in space and time, generate turbulence and enhance kinetic and potential energy dissipation, providing a possible explanation for the observed variability of the local energy dissipation in the bulk of oceanic flows, and the modulation of its probability distribution function. We show how, due to the extreme drafts, in runs with Froude numbers observable in geophysical scenarios, roughly 10% of the domain flow can account for up to 50% of the global volume dissipation, reminiscent of estimates based on oceanic models.