As a Matter of Tension: Kinetic Energy Spectra in MHD Turbulence

While magnetized turbulence is ubiquitous in many astrophysical and terrestrial systems, our understanding of even the simplest physical description of this phenomena, ideal magnetohydrodynamic (MHD) turbulence, remains substantially incomplete. In this work, we highlight the shortcomings of existing theoretical and phenomenological descriptions of MHD turbulence that focus on the joint (kinetic and magnetic) energy fluxes and spectra by demonstrating that treating these quantities separately enables fundamental insights into the dynamics of MHD turbulence. This is accomplished through the analysis of the scale-wise energy transfer over time within an implicit large eddy simulation of subsonic, super-Alfvenic MHD turbulence. Our key finding is that the kinetic energy spectrum develops a scaling of approximately k(-4/3) in the stationary regime as magnetic tension mediates large-scale kinetic to magnetic energy conversion and significantly suppresses the kinetic energy cascade. This motivates a reevaluation of existing MHD turbulence theories with respect to a more differentiated modeling of the energy fluxes.

Automated summary

This study highlights the shortcomings of existing theoretical and phenomenological descriptions of MHD turbulence and provides fundamental insights into the dynamics of MHD turbulence by treating kinetic and magnetic energies separately. By analyzing the scale-wise energy transfer in subsonic, super-Alfvenic MHD turbulence, it is found that the kinetic energy spectrum develops a specific scaling law in the stationary regime.