Dissipation-Scale Turbulence in the Solar Wind

TL;DR

This paper introduces a cascade model for solar wind turbulence that explains the spectral features and dissipation mechanisms, highlighting the role of Landau damping and instrumental limitations in observed spectra.

Contribution

The model provides a unified explanation for the spectral break, the exponential cutoff, and the variation in spectral indices in solar wind turbulence.

Findings

Spectral break corresponds to an exponential cutoff beyond which turbulence dissipates.

Instrumental sensitivity limitations can mimic power-law behavior in the dissipation range.

Variation in spectral indices from -2 to -4 is explained by Landau damping effects.

Abstract

We present a cascade model for turbulence in weakly collisional plasmas that follows the nonlinear cascade of energy from the large scales of driving in the MHD regime to the small scales of the kinetic Alfven wave regime where the turbulence is dissipated by kinetic processes. Steady-state solutions of the model for the slow solar wind yield three conclusions: (1) beyond the observed break in the magnetic energy spectrum, one expects an exponential cut-off; (2) the widely held interpretation that this dissipation range obeys power-law behavior is an artifact of instrumental sensitivity limitations; and, (3) over the range of parameters relevant to the solar wind, the observed variation of dissipation range spectral indices from -2 to -4 is naturally explained by the varying effectiveness of Landau damping, from an undamped prediction of -7/3 to a strongly damped index around -4.