Chromospheric Heating from Local Magnetic Growth and Ambipolar Diffusion Under Non-Equilibrium Conditions

TL;DR

This study uses advanced radiative MHD simulations with ambipolar diffusion and non-equilibrium hydrogen ionization to better understand chromospheric heating, showing improved agreement with IRIS observations of Mg II profiles.

Contribution

It introduces a high-resolution 3D radiative MHD model incorporating ambipolar diffusion and NEQI, advancing the understanding of chromospheric heating mechanisms.

Findings

Magnetic energy dissipates in the upper chromosphere, increasing temperature.

Including ambipolar diffusion and NEQI improves Mg II profile matching with observations.

Some discrepancies between models and observations still remain.

Abstract

The heating of the chromosphere in internetwork regions remains one of the foremost open questions in solar physics. In the present study we tackle this old problem by using a very high spatial-resolution simulation of quiet-Sun conditions performed with radiative MHD numerical models and IRIS observations. We have expanded a previously existing 3D radiative MHD numerical model of the solar atmosphere, which included self-consistently locally driven magnetic amplification in the chromosphere, by adding ambipolar diffusion and time-dependent non-equilibrium hydrogen ionization to the model. The energy of the magnetic field is dissipated in the upper chromosphere, providing a large temperature increase due to ambipolar diffusion and the non-equilibrium ionization (NEQI). At the same time, we find that adding the ambipolar diffusion and NEQI in the simulation has a minor impact on the local growth of the magnetic field in the lower chromosphere and its dynamics. Our comparison between synthesized Mg II profiles from these high spatial resolution models, with and without ambipolar diffusion and NEQI, and quiet Sun and coronal hole observations from IRIS now reveal a better correspondence. The intensity of profiles is increased and the line cores are slightly broader when ambipolar diffusion and NEQI effects are included. Therefore, the Mg II profiles are closer to those observed than in previous models, but some differences still remain.