Spectra of strong magnetohydrodynamic turbulence from high-resolution simulations

Abstract

Magnetohydrodynamic (MHD) turbulence is present in a variety of solar and astrophysical environments. Solar wind fluctuations with frequencies lower than 0.1 Hz are believed to be mostly governed by Alfvénic turbulence with particle transport depending on the power spectrum and the anisotropy of such turbulence. Recently, conflicting spectral slopes for the inertial range of MHD turbulence have been reported by different groups. Spectral shapes from earlier simulations showed that MHD turbulence is less scale-local compared with hydrodynamic turbulence. This is why higher-resolution simulations, and careful and rigorous numerical analysis is especially needed for the MHD case. In this Letter, we present two groups of simulations with resolution up to 4096 3, which are numerically well-resolved and have been analyzed with an exact and well-tested method of scaling study. Our results from both simulation groups indicate that the asymptotic power spectral slope for all energy-related quantities, such as total energy and residual energy, is around -1.7, close to Kolmogorov's -5/3. This suggests that residual energy is a constant fraction of the total energy and that in the asymptotic regime of Alfvénic turbulence magnetic and kinetic spectra have the same scaling. The -1.5 slope for energy and the -2 slope for residual energy, which have been suggested earlier, are incompatible with our numerics. © 2014. The American Astronomical Society. All rights reserved.