Simulations of Alfven wave driving of the solar chromosphere - efficient heating and spicule launching

TL;DR

This paper demonstrates through high-resolution MHD simulations that Alfvén and kink wave driving can efficiently heat the solar chromosphere and generate spicules, aligning with observed phenomena.

Contribution

It introduces a comprehensive MHD model showing how wave-driven shocks from Alfvén and kink waves can simultaneously explain chromospheric heating and spicule formation.

Findings

Wave-driven shocks produce realistic chromospheric heating rates.

Simulated spicules match observed Type-I spicule properties.

The model unifies heating and spicule formation mechanisms.

Abstract

Two of the central problems in our understanding of the solar chromosphere are how the upper chromosphere is heated and what drives spicules. Estimates of the required chromospheric heating, based on radiative and conductive losses suggest a rate of ${\sim} 0.1 \mathrm{\:erg\:cm^{-3}\:s^{-1}}$ in the lower chromosphere dropping to ${\sim} 10^{-3} \mathrm{\:erg\:cm^{-3}\:s^{-1}}$ in the upper chromosphere (\citet{Avrett1981}). The chromosphere is also permeated by spicules, higher density plasma from the lower atmosphere propelled upwards at speeds of ${\sim} 10-20 \mathrm{\:km\:s^{-1}}$, for so called Type-I spicules (\citet{Pereira2012,Zhang2012}), reaching heights of ${\sim} 3000-5000 \mathrm{\:km}$ above the photosphere. A clearer understanding of chromospheric dynamics, its heating and the formation of spicules, is thus of central importance to solar atmospheric science. For over thirty years it has been proposed that photospheric driving of MHD waves may be responsible for both heating and spicule formation. This paper presents results from a high-resolution MHD treatment of photospheric driven Alfv\'en and kink waves propagating upwards into an expanding flux tube embedded in a model chromospheric atmosphere. We show that the ponderomotive coupling from Alfv\'en and kink waves into slow modes generates shocks which both heat the upper chromosphere and drive spicules. These simulations show that wave driving of the solar chromosphere can give a local heating rate which matches observations and drive spicules consistent with Type-I observations all within a single coherent model.