A model for the non-universal power-law of the solar wind sub-ion scale magnetic spectrum

TL;DR

This paper presents a phenomenological turbulence model for kinetic Alfvén waves that explains the non-universal power-law spectra observed at sub-ion scales in the solar wind and magnetosphere, highlighting the role of Landau damping and turbulence regimes.

Contribution

It introduces a new model that captures the transition from weak to strong turbulence and accounts for non-local interactions affecting the spectral steepness.

Findings

Reproduces observed non-universal power-law spectra at sub-ion scales.

Shows the impact of Landau damping on turbulence transfer time and spectral steepening.

Identifies the dependence of spectral exponent on the ratio of Alfvén wave period to nonlinear timescale.

Abstract

A phenomenological turbulence model for kinetic Alfv\'en waves in a magnetizedcollisionless plasma, able to reproduce the non-universalpower-law spectra observed at the sub-ion scales in the solar wind and the terrestrial magnetosphere, is presented.The process of temperature homogenization along distortedmagnetic field lines, induced by Landau damping,affects the turbulencetransfer time and results in a steepening of the sub-ion power-law spectrumof critically-balanced turbulence, whose exponent is sensitive to the ratio between the Alfv\'en wave period and the nonlinear timescale. Transition from large-scaleweak turbulence to smaller scale strong turbulence is capturedand non local interactions, relevant in the case of steep spectra, are accounted for.