Energy spectra stemming from interactions of Alfven waves and turbulent eddies

TL;DR

This study numerically investigates incompressible magnetohydrodynamic turbulence, revealing energy spectra influenced by Alfven waves and turbulent eddies, with distinct large-scale and small-scale behaviors consistent with theoretical predictions.

Contribution

It provides high-resolution numerical analysis of MHD turbulence without a uniform magnetic field, highlighting the spectral effects of Alfven waves and turbulence interactions.

Findings

Energy spectrum shows two components influenced by Alfven waves and turbulence.

Large scales exhibit isotropy and Iroshnikov-Kraichnan spectral law.

Small scales display a weak turbulence spectrum with a k_{ot}^{-2} scaling.

Abstract

We present a numerical analysis of an incompressible decaying magnetohydrodynamic turbulence run on a grid of 1536^3 points. The Taylor Reynolds number at the maximum of dissipation is ~1100, and the initial condition is a superposition of large scale ABC flows and random noise at small scales, with no uniform magnetic field. The initial kinetic and magnetic energies are equal, with negligible correlation. The resulting energy spectrum is a combination of two components, each moderately resolved. Isotropy obtains in the large scales, with a spectral law compatible with the Iroshnikov-Kraichnan theory stemming from the weakening of nonlinear interactions due to Alfven waves; scaling of structure functions confirms the non-Kolmogorovian nature of the flow in this range. At small scales, weak turbulence emerges with a k_{\perp}^{-2} spectrum, the perpendicular direction referring to the local quasi-uniform magnetic field.