As a matter of tension -- kinetic energy spectra in MHD turbulence

TL;DR

This study uses simulations to analyze kinetic and magnetic energy spectra in MHD turbulence, revealing a $k^{-4/3}$ scaling in kinetic energy, which suggests the need to revise existing theories for better differentiation of energy fluxes.

Contribution

It demonstrates the importance of separately analyzing kinetic and magnetic energies in MHD turbulence and provides new insights into the kinetic energy spectrum scaling.

Findings

Kinetic energy spectrum develops a $k^{-4/3}$ scaling.

Magnetic tension suppresses the kinetic energy cascade.

Results suggest revisiting MHD turbulence theories.

Abstract

Magnetized turbulence is ubiquitous in many astrophysical and terrestrial systems but no complete, uncontested theory even in the simplest form, magnetohydrodynamics (MHD), exists. Many theories and phenomenologies focus on the joint (kinetic and magnetic) energy fluxes and spectra. We highlight the importance of treating kinetic and magnetic energies separately to shed light on MHD turbulence dynamics. We conduct an implicit large eddy simulation of subsonic, super-Alfv\'enic MHD turbulence and analyze the scale-wise energy transfer over time. Our key finding is that the kinetic energy spectrum develops a scaling of approximately $k^{-4/3}$ in the stationary regime as the kinetic energy cascade is suppressed by magnetic tension. This motivates a reevaluation of existing MHD turbulence theories with respect to a more differentiated modeling of the energy fluxes.