A&A 502, 647-660 (2009)
DOI: 10.1051/0004-6361/200811155

Bright fibrils in Ca II K

A. Pietarila¹, J. Hirzberger¹, V. Zakharov¹, and S. K. Solanki<sup>1, 2

1</sup>  Max-Planck-Institut fur Sonnensystemforschung, 37191 Katlenburg-Lindau, Germany
    e-mail: pietarila@mps.mpg.de
²  School of Space Research, Kyung Hee University, Yongin, Gyeonggi 446-701, Korea

Received 15 October 2008 / Accepted 28 March 2009

Abstract
Context. Except for the 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 K, provided the spatial-resolution is sufficiently high.
Methods. We present high spatial resolution observations of an active region in the 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 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.

Key words: Sun: chromosphere -- Sun: magnetic fields -- Sun: oscillations

© ESO 2009

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