Strong magnetohydrodynamic turbulence with cross helicity

TL;DR

This paper investigates the properties of magnetohydrodynamic turbulence with cross helicity, revealing that energy spectra scaling is unaffected by cross helicity, though amplitudes vary with it, through high-resolution simulations.

Contribution

It provides new insights into the scaling behavior of MHD turbulence with cross helicity using high-resolution numerical simulations.

Findings

Energy spectra scaling is independent of cross helicity.

E^+ and E^- spectra have the same scaling but different amplitudes.

Inherent local imbalance in MHD turbulence is confirmed.

Abstract

Magnetohydrodynamics (MHD) provides the simplest description of magnetic plasma turbulence in a variety of astrophysical and laboratory systems. MHD turbulence with nonzero cross helicity is often called imbalanced, as it implies that the energies of Alfv\'en fluctuations propagating parallel and anti-parallel the background field are not equal. Recent analytical and numerical studies have revealed that at every scale, MHD turbulence consists of regions of positive and negative cross helicity, indicating that such turbulence is inherently locally imbalanced. In this paper, results from high resolution numerical simulations of steady-state incompressible MHD turbulence, with and without cross helicity are presented. It is argued that the inertial range scaling of the energy spectra (E^+ and E^-) of fluctuations moving in opposite directions is independent of the amount of cross-helicity. When cross helicity is nonzero, E^+ and E^- maintain the same scaling, but have differing amplitudes depending on the amount of cross-helicity.