Two-dimensional Radiative Magnetohydrodynamic Simulations of Partial Ionization in the Chromosphere. II. Dynamics and Energetics of the Low Solar Atmosphere

TL;DR

This study uses advanced 2.5D radiative MHD simulations to explore how ion-neutral interactions, especially ambipolar diffusion, influence the dynamics and heating in the solar chromosphere and transition region.

Contribution

The paper extends the Bifrost code to include ion-neutral effects via the Generalized Ohm's Law, revealing their significant impact on chromospheric magneto-thermodynamics.

Findings

Ambipolar diffusion increases chromospheric temperature.

Large ambipolar diffusion causes horizontal magnetic field diffusion into the chromosphere.

Ambipolar diffusion leads to longer, faster spicules and plasma heating.

Abstract

We investigate the effects of interactions between ions and neutrals on the chromosphere and overlying corona using 2.5D radiative MHD simulations with the Bifrost code. We have extended the code capabilities implementing ion-neutral interaction effects using the Generalized Ohm's Law, i.e., we include the Hall term and the ambipolar diffusion (Pedersen dissipation) in the induction equation. Our models span from the upper convection zone to the corona, with the photosphere, chromosphere and transition region partially ionized. Our simulations reveal that the interactions between ionized particles and neutral particles have important consequences for the magneto-thermodynamics of these modeled layers: 1) ambipolar diffusion increases the temperature in the chromosphere; 2) sporadically the horizontal magnetic field in the photosphere is diffused into the chromosphere due to the large ambipolar diffusion; 3) ambipolar diffusion concentrates electrical currents leading to more violent jets and reconnection processes, resulting in 3a) the formation of longer and faster spicules, 3b) heating of plasma during the spicule evolution, and 3c) decoupling of the plasma and magnetic field in spicules. Our results indicate that ambipolar diffusion is a critical ingredient for understanding the magneto-thermo-dynamic properties in the chromosphere and transition region. The numerical simulations have been made publicly available, similar to previous Bifrost simulations. This will allow the community to study realistic numerical simulations with a wider range of magnetic field configurations and physics modules than previously possible.