Using MHD simulations to model H-alpha and UV spectral lines for interpretation of IRIS and NST data

TL;DR

This paper uses non-LTE radiative transfer modeling combined with MHD simulations to interpret spectral lines from solar observations, revealing correlations useful for diagnosing chromospheric oscillations.

Contribution

It introduces a new method linking spectral line variations to atmospheric parameters using MHD simulations and non-LTE modeling for solar data interpretation.

Findings

Correlation between line intensity power spectra and atmospheric parameters.

Identification of MHD waves through spectral line analysis.

Potential for improved diagnostics of chromospheric oscillations.

Abstract

We present results of non-LTE modeling of H-alpha 6563 A and Mg II k&h 2796 A and 2803 A lines. This modeling is important for interpretation of coordinated observations from the recently launched NASA's IRIS mission and from the New Solar Telescope at Big Bear Solar Observatory. Among available codes for the non-LTE modeling, the RH code is chosen as the most appropriate for modeling of the line profiles. The most suitable Hydrogen and Magnesium atomic models are selected by performing several tests of the code. The influence of the ionization degree on the line profiles is also studied. Radiative-MHD simulations of the solar atmosphere, obtained with the Bifrost code, are used as input data for calculation of synthetic spectra of the H-alpha and Mg II h&k lines for particular locations evolving with time. The spectral line variations reveal the presence of MHD waves in the simulation results. We construct oscillation power spectra of the line intensity for different wavelength, and compare these with the corresponding height-dependent power spectra of atmospheric parameters from the simulations. We find correlations between the power spectra of intensities of the line profiles at certain wavelengths and the power spectra of the atmospheric parameters at the tau-unity heights for these wavelengths. These results provide a new diagnostic method of chromospheric oscillations; however, larger amounts of data are needed to confirm these correlations.