Effect of ion-neutral collisions in simulations of emerging active regions

TL;DR

This study uses advanced 2.5D simulations to explore how ion-neutral collisions influence magnetic flux emergence in the solar atmosphere, revealing effects on flux transport, plasma dynamics, and magnetic energy transfer.

Contribution

It introduces ion-neutral collision effects into flux emergence models with realistic physics, showing their impact on flux transport and energy in the solar atmosphere.

Findings

Ionization reduces flux tube rise speed.

Neutral Hydrogen increases magnetic flux in the corona.

Ion-neutral collisions decrease free magnetic energy in the corona.

Abstract

We present results of 2.5D numerical simulations of the emergence of sub-surface magnetic flux into the solar atmosphere, with emerging flux regions ranging from $10^{18}$ to $10^{21}$ Mx, representing both ephemeral and active regions. We include the presence of neutral Hydrogen in the governing equations, improve upon previous models by including the ionization in the equation of state, and use a more realistic convection zone model. We find that ionization and recombination of plasma during the rise of a convection zone flux tube reduces the rise speed of the tube's axis. The presence of neutral Hydrogen allows the effective flow of mass across fieldlines, by the addition of a Pedersen resistivity to the generalized Ohm's law, which dissipates current perpendicular to the magnetic field. This causes an increase of up to 10% in the amount of magnetic in-plane flux supplied to the corona and a reduction of up to 89% in the amount of sub-surface plasma brought up into the corona. However, it also reduces the amount of free magnetic energy supplied to the corona, and thus does not positively affect the likelihood of creating unstable coronal structures.