Anisotropic scaling of magnetohydrodynamic turbulence

TL;DR

This paper analyzes the anisotropic scaling of magnetic fluctuations in solar wind turbulence using wavelet techniques, revealing different spectral behaviors depending on the magnetic field orientation.

Contribution

It introduces a novel wavelet method to quantify anisotropic power and scaling in MHD turbulence from spacecraft data, highlighting the spectral index variations with field direction.

Findings

Spectral index near 2 when magnetic field is parallel to flow.

Most power contained in wavevectors at large angles with spectral index 5/3.

First quantitative estimate of anisotropic power using wavelet analysis in this context.

Abstract

We present a quantitative estimate of the anisotropic power and scaling of magnetic field fluctuations in inertial range magnetohydrodynamic turbulence, using a novel wavelet technique applied to spacecraft measurements in the solar wind. We show for the first time that, when the local magnetic field direction is parallel to the flow, the spacecraft-frame spectrum has a spectral index near 2. This can be interpreted as the signature of a population of fluctuations in field-parallel wavenumbers with a $k_{\parallel}^{-2}$ spectrum but is also consistent with the presence of a "critical balance" style turbulent cascade. We also find, in common with previous studies, that most of the power is contained in wavevectors at large angles to the local magnetic field and that this component of the turbulence has a spectral index of 5/3.