Non-equilibrium helium ionization in an MHD simulation of the solar atmosphere

Abstract

The ionization state of the gas in the dynamic solar chromosphere can depart strongly from the instantaneous statistical equilibrium commonly assumed in numerical modeling. We improve on earlier simulations of the solar atmosphere that only included non-equilbrium hydrogen ionization by performing a 2D radiation-magneto-hydrodynamics simulation featuring non-equilibrium ionization of both hydrogen and helium. The simulation includes the effect of hydrogen Lyman-$\alpha$ and the EUV radiation from the corona on the ionization and heating of the atmosphere. Details on code implementation are given. We obtain helium ion fractions that are far from their equilibrium values. Comparison with models with LTE ionization shows that non-equilibrium helium ionization leads to higher temperatures in wave fronts and lower temperatures in the gas between shocks. Assuming LTE ionization results in a thermostat-like behaviour with matter accumulating around the temperatures where the LTE ionization fractions change rapidly. Comparison of DEM curves computed from our models shows that non-equilibrium ionization leads to more radiating material in the temperature range 11-18 kK compared to models with LTE helium ionization. We conclude that non-equilbrium helium ionization is important for the dynamics and thermal structure of the upper chromosphere and transition region. It might also help resolve the problem that intensities of chromospheric lines computed from current models are smaller than those observed.

Accepted for publication in Astrophysical Journal

References in corpus (8)

• The FIP and Inverse FIP Effects in Solar and Stellar Coronae
• A Contemporary View of Coronal Heating
• A publicly available simulation of an enhanced network region of the Sun
• Non-equilibrium hydrogen ionization in 2D simulations of the solar atmosphere
• Why Is Non-thermal Line Broadening of Spectral Lines in The Lower Transition Region of the Sun Independent of Spatial Resolution?
• The Formation of IRIS Diagnostics. VII. The Formation of the OI 135.56 nm Line in the Solar Atmosphere
• Coronal energy input and dissipation in a solar active region 3D MHD model
• Simulations of Stellar Magnetoconvection using the Radiative MHD Code `StellarBox'

Cited by in corpus (38)

• Partially Ionized Plasmas in Astrophysics
• The MUSCLES Treasury Survey IV: Scaling Relations for Ultraviolet, Ca II K, and Energetic Particle Fluxes from M Dwarfs
• Three-dimensional Magnetohydrodynamic Simulation of the Formation of Solar Chromospheric Jets with Twisted Magnetic Field Lines
• Probing the physics of the solar atmosphere with the Multi-slit Solar Explorer (MUSE): I. Coronal Heating
• Three-dimensional modeling of the Ca II H&K lines in the solar atmosphere
• The GAPS programme at TNG XXII. The GIARPS view of the extended helium atmosphere of HD189733 b accounting for stellar activity
• Non-Equilibrium Processes in the Solar Corona, Transition Region, Flares, and Solar Wind \textit{(Invited Review)}
• Ion-neutral interactions and non-equilibrium ionization in the solar chromosphere
• Chromospheric Extension of the MURaM Code
• Three-dimensional modeling of chromospheric spectral lines in a simulated active region
• The cause of spatial structure in solar He I 1083 nm multiplet images
• Nonequilibrium ionization and ambipolar diffusion in solar magnetic flux emergence processes
• A First Comparison of Millimeter Continuum and Mg II Ultraviolet Line Emission from the Solar Chromosphere
• Formation of the helium EUV resonance lines
• Ambipolar diffusion in the Bifrost code
• He I 10830 Å Dimming During Solar Flares, I. The Crucial Role of Non-Thermal Collisional Ionisations
• Radiation hydrodynamics in simulations of the solar atmosphere
• The Formation Height of Millimeter-wavelength Emission in the Solar Chromosphere
• Numerical simulations and observations of Mg II in the solar chromosphere
• On the importance of the nonequilibrium ionization of Si IV and O IV and the line-of-sight in solar surges
• The impact of multi-fluid effects in the solar chromosphere on the ponderomotive force under LTE and NEQ ionization conditions
• Modeling Mg II during Solar Flares. II. Non-equilibrium Effects
• ALMA and IRIS Observations of the Solar Chromosphere I: an On-Disk Type II Spicule
• Multi-Fluid Simulations of Upper Chromospheric Magnetic Reconnection with Helium-Hydrogen mixture
• Capabilities of bisector analysis of the Si I 10827 A line for estimating line-of-sight velocities in the quiet Sun
• Chromospheric Heating from Local Magnetic Growth and Ambipolar Diffusion Under Non-Equilibrium Conditions
• A benchmark study of atomic models for the transition region against quiet Sun observations
• Comparison of Solar Fine Structure Observed Simultaneously in Ly-α and Mg II h
• Structure and dynamics of the internetwork solar chromosphere: results of a small-scale dynamo simulation
• Formation of the Mg II h and k polarization profiles in a solar plage model and their suitability to infer magnetic fields
• Doppler shifts of spectral lines formed in the solar transition region and corona
• Multi-fluid Simulation of Solar Chromospheric Turbulence and Heating Due to the Thermal Farley-Buneman Instability
• Chromosphere of the quiet sun -- I. Shock and current-sheet dynamics and heating
• Magnetic Imaging of the Outer Solar Atmosphere (MImOSA): Unlocking the driver of the dynamics in the upper solar atmosphere
• A new view of the solar interface region from the Interface Region Imaging Spectrograph (IRIS)
• Modeling brightness temperature of sunspots using ALMA single-dish observations
• The multi-thermal chromosphere: inversions of ALMA and IRIS data
• A single frequency approach to nonequilibrium modeling of the chromosphere