Parallel Electric Field Spectrum of Solar Wind Turbulence

TL;DR

This study analyzes satellite data to characterize the spectrum of parallel electric field turbulence in the solar wind, revealing power-law behaviors and spectral flattening near ion scales.

Contribution

It provides the first reliable observations of parallel electric field turbulence in the undisturbed solar wind, highlighting spectral similarities and differences with perpendicular turbulence.

Findings

Parallel electric field spectra follow a -5/3 power law below ion scales.

Spectral flattening occurs near the ion gyroscale (~0.1 Hz).

At higher frequencies, spectra steepen to -2.1 to -2.8, indicating kinetic Alfven turbulence.

Abstract

By searching through more than 10 satellite-years of THEMIS and Cluster data, three reliable examples of parallel electric field turbulence in the undisturbed solar wind have been found. The perpendicular and parallel electric field spectra in these examples have similar shapes and amplitudes, even at large scales (frequencies below the ion gyroscale) where Alfvenic turbulence with no parallel electric field component is thought to dominate. The spectra of the parallel electric field fluctuations are power laws with exponents near -5/3 below the ion scales (~ 0.1 Hz), and with a flattening of the spectrum in the vicinity of this frequency. At small scales (above a few Hz), the spectra are steeper than -5/3 with values in the range of -2.1 to -2.8. These steeper slopes are consistent with expectations for kinetic Alfven turbulence, although their amplitude relative to the perpendicular fluctuations is larger than expected.