Scale dependent anisotropy of electric field fluctuations in solar wind turbulence

TL;DR

This study investigates how electric field fluctuation properties in solar wind turbulence vary with angle and scale, revealing anisotropic behaviors and differences between electric and magnetic spectra using Cluster spacecraft data.

Contribution

It provides the first detailed scale-dependent analysis of electric field anisotropy in solar wind turbulence using wavelet techniques and multi-year spacecraft data.

Findings

Electric power spectra show prominent anisotropy with respect to magnetic field direction.

Parallel electric fluctuations are steeper but have greater power than perpendicular ones.

Below 0.1 Hz, electric spectra deviate from magnetic spectra, indicating Alfvénic turbulence.

Abstract

We study the variation of average powers and spectral indices of electric field fluctuations with respect to the angle between average flow direction and the mean magnetic field in solar wind turbulence. Cluster spacecraft data from the years 2002 and 2007 are used for the present analysis. We perform a scale dependent study with respect to the local mean magnetic field using wavelet analysis technique. Prominent anisotropies are found for both the spectral index and power levels of the electric power spectra. Similar to the magnetic field fluctuations, the parallel (or antiparallel) electric fluctuation spectrum is found to be steeper than the perpendicular spectrum. However the parallel (or antiparallel) electric power is found to be greater than the perpendicular one. Below 0.1 Hz, the slope of the parallel electric power spectra deviates substantially from that of the total magnetic power spectra, supporting the existence of Alfv\'enic turbulence.