Linear and Non-Linear Landau Resonance of Kinetic Alfv\'en Waves: Consequences for Electron Distribution and Wave Spectrum in the Solar Wind

TL;DR

This paper investigates how kinetic Alfvén wave turbulence and non-Maxwellian electron distributions influence solar wind plasma dynamics, leading to spectrum steepening consistent with observations.

Contribution

It introduces a generalized nonlinear wave scattering process for short wavelengths and demonstrates its dominance over three-wave decay in solar wind conditions.

Findings

Formation of a plateau in electron distribution reduces Landau damping

Nonlinear scattering dominates wave interactions at short wavelengths

Wave spectrum steepens between inertial and dissipation ranges

Abstract

Kinetic Alfven wave turbulence in solar wind is considered and it is shown that non-Maxwellian electron distribution function has a significant effect on the dynamics of the solar wind plasmas. Linear Landau damping leads to the formation of a plateau in the parallel electron distribution function which diminishes the Landau damping rate significantly. Nonlinear scattering of waves by plasma particles is generalized to short wavelengths and it is found that for the solar wind parameters this scattering is the dominant process as compared to three wave decay and coalescence in the wave vector range . Incorporation of these effects lead to the steepening of the wave spectrum between the inertial and the dissipation ranges with a spectral index between 2 and 3. This region can be labeled as the scattering range. Such steepening has been observed in the solar wind plasmas.