Kinetic Turbulence in the Terrestrial Magnetosheath: Cluster Observations

TL;DR

This study analyzes subproton and electron scale turbulence in Earth's magnetosheath using Cluster spacecraft data, revealing spectral breaks and steep power-law spectra that inform models of kinetic plasma turbulence.

Contribution

First statistical analysis of electron and subproton scale turbulence in the magnetosheath, identifying spectral breaks and steep power-law spectra in space plasma turbulence.

Findings

Spectral breaks near electron scale separate dispersive and dissipation ranges.

Break frequencies correlate with electron gyroscale, not inertial length.

Observed steep spectra with slopes as low as -7.5.

Abstract

We present a first statistical study of subproton and electron scales turbulence in the terrestrial magnetosheath using the Cluster Search Coil Magnetometer (SCM) waveforms of the STAFF instrument measured in the frequency range [1,180] Hz. It is found that clear spectral breaks exist near the electron scale, which separate two power-law like frequency bands referred to as the dispersive and the electron dissipation ranges. The frequencies of the breaks f_b are shown to be well correlated with the electron gyroscale \rho_e rather than with the electron inertial length de. The distribution of the slopes below fb was found to be narrow and peaks near -2.9, while that of the slopes above fb was found broader, peaks near -5.2 and has values as low as -7.5. This is the first time that such steep power-law spectra are reported in space plasma turbulence. These observations provide strong constraints on theoretical modeling of kinetic turbulence and dissipation in collisionless magnetized plasmas.