Three-dimensional non-LTE radiative transfer computation of the Ca 8542 infrared line from a radiation-MHD simulation

TL;DR

This study employs 3D non-LTE radiative transfer modeling on a radiation-MHD simulation to interpret solar chromosphere imagery in the Ca II 8542 infrared line, comparing synthetic images with actual observations.

Contribution

It introduces a comprehensive 3D non-LTE radiative transfer approach applied to a radiation-MHD simulation for the Ca II 8542 line, enhancing understanding of chromospheric features.

Findings

Simulation reproduces observed dark patches caused by Doppler shifts

Brightenings in the line core are linked to upward-propagating shocks

Synthetic line core is narrower than observed, indicating unresolved small-scale motions

Abstract

Interpretation of imagery of the solar chromosphere in the widely used \CaIIIR infrared line is hampered by its complex, three-dimensional and non-LTE formation. Forward modelling is required to aid understanding. We use a 3D non-LTE radiative transfer code to compute synthetic \CaIIIR images from a radiation-MHD simulation of the solar atmosphere spanning from the convection zone to the corona. We compare the simulation with observations obtained with the CRISP filter at the Swedish 1--m Solar Telescope. We find that the simulation reproduces dark patches in the blue line wing caused by Doppler shifts, brightenings in the line core caused by upward-propagating shocks and thin dark elongated structures in the line core that form the interface between upward and downward gas motion in the chromosphere. The synthetic line core is narrower than the observed one, indicating that the sun exhibits both more vigorous large-scale dynamics as well as small scale motions that are not resolved within the simulation, presumably owing to a lack of spatial resolution.