Anisotropy of Imbalanced Alfvenic Turbulence in Fast Solar Wind

TL;DR

This study measures the scale-dependent anisotropy of Elsasser variables in imbalanced fast solar wind turbulence, revealing different anisotropic behaviors for dominant and sub-dominant modes and challenging existing theories.

Contribution

First measurement of scale-dependent power anisotropy of Elsasser variables in imbalanced fast solar wind turbulence, highlighting new anisotropic behaviors.

Findings

Dominant Elsasser mode is isotropic at low frequencies and anisotropic at high frequencies.

Sub-dominant Elsasser mode remains anisotropic across scales, but scale-independent.

Two subranges with different scalings within the inertial range.

Abstract

We present the first measurement of the scale-dependent power anisotropy of Elsasser variables in imbalanced fast solar wind turbulence. The dominant Elsasser mode is isotropic at lower spacecraft frequencies but becomes increasingly anisotropic at higher frequencies. The sub-dominant mode is anisotropic throughout, but in a scale-independent way (at higher frequencies). There are two distinct subranges exhibiting different scalings within what is normally considered the inertial range. The low Alfven ratio and shallow scaling of the sub-dominant Elsasser mode suggest an interpretation of the observed discrepancy between the velocity and magnetic field scalings. The total energy is dominated by the latter. These results do not appear to be fully explained by any of the current theories of incompressible imbalanced MHD turbulence.