Role of cross helicity in magnetohydrodynamic turbulence

TL;DR

This study uses high-resolution simulations to explore how cross helicity influences the structure and spectra of incompressible MHD turbulence, revealing the significance of aligned and anti-aligned fluctuations.

Contribution

It provides new insights into the role of cross helicity in MHD turbulence, including an analytical explanation for observed phenomena.

Findings

Regions of positive and negative cross-helicity are prevalent in turbulence.

Spectral and structural properties vary with cross-helicity regions.

Results align with balanced turbulence when averaged over all regions.

Abstract

Strong incompressible three-dimensional magnetohydrodynamic turbulence is investigated by means of high resolution direct numerical simulations. The simulations show that the configuration space is characterized by regions of positive and negative cross-helicity, corresponding to highly aligned or anti-aligned velocity and magnetic field fluctuations, even when the average cross-helicity is zero. To elucidate the role of cross-helicity, the spectra and structure of turbulence are obtained in imbalanced regions where cross-helicity is non-zero. When averaged over regions of positive and negative cross-helicity, the result is consistent with the simulations of balanced turbulence. An analytical explanation for the obtained results is proposed.