Bright fibrils in Ca II K

TL;DR

This study reveals that bright fibrils are common in Ca II K observations at high spatial resolution, showing their connection to photospheric magnetic features and their role in chromospheric dynamics.

Contribution

The paper demonstrates the presence of narrow, bright fibrils in Ca II K and explores their connection to photospheric magnetic structures and chromospheric oscillations.

Findings

Bright fibrils are prevalent in Ca II K at high resolution.

Fibril footpoints are linked to photospheric magnetic features.

Fibrils can suppress or channel oscillations in the chromosphere.

Abstract

Context: Except for the Ca II resonance lines, fibrils are ubiquitously present in most high-resolution observations of chromospheric lines. Aims: We show that fibrils are also a prevailing feature in Ca II K, provided the spatial-resolution is sufficiently high. Methods: We present high spatial resolution observations of an active region in the Ca I} K line from the Swedish Solar Telescope. Through a comparison between photospheric intensity and magnetic field data, we study the connection between bright chromospheric fibrils and photospheric structures. Additionally, using Fourier analysis we study how the fibrils are linked to the observed dynamics. Results: We find that very narrow, bright fibrils are a prevailing feature over large portions of the observed field. We also find a clear connection between the fibril footpoints and photospheric magnetic features. We show that the fibrils play two distinct roles in the observed dynamics: depending on their location they can act as a canopy suppressing oscillations or they can channel low-frequency oscillations into the chromosphere. Conclusions: The Ca II K fibrils share many characteristics with fibrils observed in other chromospheric lines, but some features, such as the very small widths, are unique to these observations.