Kinetic Alfv\'{e}n turbulence below and above ion-cyclotron frequency

TL;DR

This paper investigates how anisotropic dispersive effects and turbulence intermittency influence the spectral characteristics of kinetic Alfvén turbulence around the ion-cyclotron frequency, revealing that these factors shape the observed spectral indices in space plasmas.

Contribution

It provides a comprehensive analysis of the combined effects of dispersion and intermittency on kinetic Alfvén turbulence spectra, aligning theoretical predictions with solar wind observations.

Findings

Spectral indices range from -2 to -3 due to dispersion and intermittency effects.

Intermittent turbulence spectra are confined to a narrower index range of [-7/3, -3].

The observed spectra in the solar wind are mainly shaped by dispersion and intermittency, with minor damping effects.

Abstract

Alfv\'{e}nic turbulent cascade perpendicular and parallel to the background magnetic field is studied accounting for anisotropic dispersive effects and turbulent intermittency. The perpendicular dispersion and intermittency make the perpendicular-wavenumber magnetic spectra steeper and speed up production of high ion-cyclotron frequencies by the turbulent cascade. On the contrary, the parallel dispersion makes the spectra flatter and decelerate the frequency cascade above the ion-cyclotron frequency. Competition of the above factors results in spectral indices distributed in the interval [-2,-3], where -2 is the index of high-frequency space-filling turbulence, and -3 is the index of low-frequency intermittent turbulence formed by tube-like fluctuations. Spectra of fully intermittent turbulence fill a narrower range of spectral indices [-7/3,-3], which almost coincides with the range of indexes measured in the solar wind. This suggests that the kinetic-scale turbulent spectra are shaped mainly by dispersion and intermittency. A small mismatch with measured indexes of about 0.1 can be associated with damping effects not studied here.