Density Fluctuation Spectrum of Solar Wind Turbulence between Ion and Electron Scales

TL;DR

This study measures the density fluctuation spectrum of solar wind turbulence between ion and electron scales, revealing a steep spectral index that suggests increased intermittency or damping, independent of pressure anisotropy thresholds.

Contribution

It provides the first detailed measurement of the density fluctuation spectral index between ion and electron scales in solar wind turbulence, highlighting its steepness and independence from instability thresholds.

Findings

Spectral index at 1 AU is approximately -2.75.

Steep spectra indicate increased intermittency or damping.

Spectral features are inherent to the turbulent cascade, unaffected by pressure anisotropy thresholds.

Abstract

We present a measurement of the spectral index of density fluctuations between ion and electron scales in solar wind turbulence using the EFI instrument on the ARTEMIS spacecraft. The mean spectral index at 1 AU was found to be -2.75 +/- 0.06, steeper than predictions for pure whistler or kinetic Alfven wave turbulence, but consistent with previous magnetic field measurements. The steep spectra are also consistent with expectations of increased intermittency or damping of some of the turbulent energy over this range of scales. Neither the spectral index nor the flattening of the density spectra before ion scales were found to depend on the proximity to the pressure anisotropy instability thresholds, suggesting that they are features inherent to the turbulent cascade.