Characterization of local energy transfer in large-scale intermittent stratified turbulent flows via coarse graining

TL;DR

This paper investigates how extreme vertical velocity drafts in stratified turbulent flows influence local energy transfer across scales, revealing their role in enhancing energy exchanges and turbulence intermittency in geophysical flows.

Contribution

It refines a classical coarse-graining method to analyze local energy transfer in stratified turbulence, highlighting the impact of vertical drafts on energy exchanges.

Findings

Vertical drafts trigger both upscale and downscale energy transfers.

Energy transfer strength depends on the intensity of vertical velocity.

Vertical drafts enhance coupling between kinetic and potential energies.

Abstract

Recent studies based on simulations of the Boussinesq equations indicate that stratified turbulent flows can develop large-scale intermittency in the velocity and temperature fields, as detected in the atmosphere and oceans. In particular, emerging powerful vertical drafts were found to generate local turbulence, proving necessary for stratified flows to dissipate the energy as efficiently as homogeneous isotropic turbulent flows. The existence of regions characterized by enhanced turbulence and dissipation, as observed, for instance, in the ocean, requires appropriate tools to assess how energy is transferred across the scales and at the same time locally in the physical space. After refining a classical space-filtering procedure, here we investigate the feedback of extreme vertical velocity drafts on energy transfer and exchanges in subdomains of simulations of stably stratified flows of geophysical interest. Our analysis shows that vertical drafts are indeed able to trigger upscale and downscale energy transfers, strengthening the coupling between kinetic and potential energies at certain scales, depending on the intensity of the local vertical velocity.