A Kinetic Model of Solar Wind Generation and Heating by Kinetic Alfv\'en Wave Turbulence

TL;DR

This paper develops a kinetic model for solar wind proton heating via Alfvén wave turbulence, incorporating various physical effects, but finds the resulting speeds and temperatures insufficient for fast solar wind, suggesting future model improvements.

Contribution

The study introduces a comprehensive kinetic model including gravity, electric fields, and wave effects to analyze proton heating in the solar wind, highlighting limitations of current turbulence spectra.

Findings

Proton distributions develop parallel extensions due to Landau resonance.

Perpendicular heating remains minimal under current parameters.

Resulting speeds and temperatures are below those needed for fast solar wind.

Abstract

We present results from a kinetic model of collisionless gyrotropic coronal hole protons heated by cyclotron and Landau resonant dissipation of critically balanced kinetic Alfv\'en waves. The model incorporates the kinetic effects of gravity, ambipolar electric field, ponderomotive force of the large-scale Alfv\'en waves and the mirror force in a super-radially expanding flux tube. The flow speed is self- consistently obtained as the bulk flow of the proton distribution. Two cases, taking the intensities of the turbulent spectra to be balanced in the parallel propagation direction or imbalanced at a ratio of 9:1 show almost no difference. The distributions develop parallel extensions outward due to the Landau resonance, but exhibit very little perpendicular heating under the parameter choices used here. The speeds and temperatures fall well short of the requirements for a fast solar wind. Rather than continuing to explore the parameter space of this system, we propose that a modified model using turbulent spectra based on the recent helicity barrier scenario would be an appropriate next step.