Small-scale structure and dynamics of the lower solar atmosphere

TL;DR

This paper discusses the dynamic small-scale structures of the solar chromosphere, comparing high-resolution observations with advanced simulations, and highlights the need for improved radiative transfer modeling for better understanding.

Contribution

It emphasizes the importance of combining observations with detailed simulations and discusses the challenges in radiative transfer calculations for the solar chromosphere.

Findings

Simulations show a mesh-like pattern of shock fronts and post-shock regions.

High-resolution observations reveal small-scale bright and dark structures.

Qualitative comparisons are currently the main method due to computational challenges.

Abstract

The chromosphere of the quiet Sun is a highly intermittent and dynamic phenomenon. Three-dimensional radiation (magneto-)hydrodynamic simulations exhibit a mesh-like pattern of hot shock fronts and cool expanding post-shock regions in the sub-canopy part of the inter-network. This domain might be called "fluctosphere". The pattern is produced by propagating shock waves, which are excited at the top of the convection zone and in the photospheric overshoot layer. New high-resolution observations reveal a ubiquitous small-scale pattern of bright structures and dark regions in-between. Although it qualitatively resembles the picture seen in models, more observations - e.g. with the future ALMA - are needed for thorough comparisons with present and future models. Quantitative comparisons demand for synthetic intensity maps and spectra for the three-dimensional (magneto-)hydrodynamic simulations. The necessary radiative transfer calculations, which have to take into account deviations from local thermodynamic equilibrium, are computationally very involved so that no reliable results have been produced so far. Until this task becomes feasible, we have to rely on careful qualitative comparisons of simulations and observations. Here we discuss what effects have to be considered for such a comparison. Nevertheless we are now on the verge of assembling a comprehensive picture of the solar chromosphere in inter-network regions as dynamic interplay of shock waves and structuring and guiding magnetic fields.