On the spatio-temporal behavior of magnetohydrodynamic turbulence in a magnetized plasma

TL;DR

This study uses direct numerical simulations to analyze how magnetic field fluctuations in magnetohydrodynamic turbulence vary over space and time, revealing dominant sweeping effects and Alfvénic influences depending on magnetic field strength.

Contribution

It provides a detailed analysis of the spatio-temporal behavior of magnetic fluctuations in MHD turbulence across different magnetic field regimes, highlighting the dominant decorrelation mechanisms.

Findings

Time decorrelations are mainly due to sweeping effects.

Alfvénic effects dominate at high magnetic fields and aligned wave vectors.

The correlation functions vary with magnetic field strength and orientation.

Abstract

Using direct numerical simulations of three-dimensional magnetohydrodynamic (MHD) turbulence the spatio-temporal behavior of magnetic field fluctuations is analyzed. Cases with relatively small, medium and large values of a mean background magnetic field are considered. The (wavenumber) scale dependent time correlation function is directly computed for different simulations, varying the mean magnetic field value. From this correlation function the time decorrelation is computed and compared with different theoretical times, namely, the local non-linear time, the random sweeping time, and the Alfv\'enic time, the latter being a wave effect. It is observed that time decorrelations are dominated by sweeping effects, and only at large values of the mean magnetic field and for wave vectors mainly aligned with this field time decorrelations are controlled by Alfv\'enic effects.