The Structure of Energy Fluxes in Wave Turbulence

TL;DR

This paper introduces a new formalism for calculating energy fluxes in wave turbulence systems, applicable to both isotropic and anisotropic cases, and provides insights into energy transfer pathways without relying on traditional assumptions.

Contribution

The paper develops a general formalism for energy flux calculation in wave turbulence, extending analysis to non-stationary, non-scale-invariant, and non-local interactions.

Findings

Re-derived standard energy flux formula for isotropic systems.

Quantified locality of energy transfers in surface capillary waves.

Characterized energy pathways in oceanic internal wavefield.

Abstract

We calculate the net energy per unit time exchanged between two sets of modes in a generic system governed by a three-wave kinetic equation. Our calculation is based on the property of detailed energy conservation of the triadic resonant interactions. In a first application to isotropic systems, we rederive the standard formula for the energy flux as a particular case for adjacent sets. We then exploit the new formalism to quantify the level of locality of the energy transfers in the example of surface capillary waves. A second application to anisotropic wave systems expands the currently available set of tools to investigate magnitude and direction of the energy fluxes in these systems. We illustrate the use of the formalism by characterizing the energy pathways in the oceanic internal wavefield. Our proposed approach, unlike traditional approaches, is not limited to stationarity, scale-invariance and strict locality. In addition, we define a number $w$ that quantifies the scale separation necessary for two sets of modes to be energetically disconnected, with potential consequences in the interpretation of wave-turbulence experiments. The methodology presented here provides a general, simple and systematic approach to energy fluxes in wave turbulence.