---
author:
- 'Johan P. Bj[ø]{}rgen, Jorrit Leenaarts, Matthias Rempel, Mark C. M. Cheung, Sanja Danilovic, Jaime de la Cruz Rodríguez, and Andrii V. Sukhorukov'
bibliography:
- 'article.bib'
date: 'Received; Accepted '
title: 'Three-dimensional modeling of chromospheric spectral lines in a simulated active region'
---

Introduction {#sec:intro}
============

[The chromosphere above active regions exhibits various dynamic phenomena. The most prominent features in quiescent periods of active region evolution are *long fibrils*.]{} [Their existence was revealed already with the early solar observations that sampled [H$\alpha$]{} line center [@1964PhDT........83B; @1976SoPh...50...37M].]{} [Later, with improved spectral and spatial resolution, a similar scene was found in other chromospheric lines such as Ca <span style="font-variant:small-caps;">ii</span> 8542 Å  and [K]{}. ]{} [It is still, however not clear how they come about. Are they visible in chromospheric lines because of the density corrugations [@2012ApJ...749..136L] or do they outline magnetic tangential discontinuities where current sheets are formed [@2011ApJ...730L...4J]?]{} [The most recently proposed scenario is that the long fibrils are actually contrails where hot material shoots up as a consequence of energetic events happening lower down .]{} [It is also unclear if and how well fibrils follow the magnetic field lines ?]{} [Answering this question is crucial for chromospheric seismology 