Interpreting Power Anisotropy Measurements in Plasma Turbulence

TL;DR

This paper derives a relationship between power and wavevector anisotropy in plasma turbulence, aiding the interpretation of solar wind measurements and understanding turbulence behavior across different scales.

Contribution

It introduces a method to interpret plasma turbulence measurements by relating power anisotropy to wavevector anisotropy, considering shape anisotropy and spectral break points.

Findings

Power anisotropy relates to wavevector anisotropy in plasma turbulence.

Spectral break points differ in parallel and perpendicular directions due to anisotropy.

Model spectra align with solar wind observations, highlighting anisotropic cascade processes.

Abstract

A relationship is derived between power anisotropy and wavevector anisotropy in turbulent fluctuations. This can be used to interpret plasma turbulence measurements, for example in the solar wind. If fluctuations are anisotropic in shape then the ion gyroscale break point in spectra in the directions parallel and perpendicular to the magnetic field would not occur at the same frequency, and similarly for the electron gyroscale break point. This is an important consideration when interpreting solar wind observations in terms of anisotropic turbulence theories. Model magnetic field power spectra are presented assuming a cascade of critically balanced Alfven waves in the inertial range and kinetic Alfven waves in the dissipation range. The variation of power anisotropy with scale is compared to existing solar wind measurements and the similarities and differences are discussed.