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Issue A&A
Volume 507, Number 1, November III 2009
Page(s) L9 - L12
Section Letters
DOI http://dx.doi.org/10.1051/0004-6361/200913380
Published online 21 October 2009

A&A 507, L9-L12 (2009)
DOI: 10.1051/0004-6361/200913380

Letter

Small-scale swirl events in the quiet Sun chromosphere

S. Wedemeyer-Böhm1, 2 and L. Rouppe van der Voort1

1  Institute of Theoretical Astrophysics, University of Oslo, PO Box 1029 Blindern, 0315 Oslo, Norway
    e-mail: sven.wedemeyer-bohm@astro.uio.no
2  Center of Mathematics for Applications, University of Oslo, Box 1053 Blindern, 0316 Oslo, Norway

Received 30 September 2009 / Accepted 14 October 2009

Abstract
Context. Recent progress in instrumentation enables solar observations with high resolution simultaneously in the spatial, temporal, and spectral domains.
Aims. We use such high-resolution observations to study small-scale structures and dynamics in the chromosphere of the quiet Sun.
Methods. We analyse time series of spectral scans through the Ca II 854.2 nm spectral line obtained with the CRISP instrument at the Swedish 1-m Solar Telescope. The targets are quiet Sun regions inside coronal holes close to disc-centre.
Results. The line core maps exhibit relatively few fibrils compared to what is normally observed in quiet Sun regions outside coronal holes. The time series show a chaotic and dynamic scene that includes spatially confined “swirl” events. These events feature dark and bright rotating patches, which can consist of arcs, spiral arms, rings or ring fragments. The width of the fragments typically appears to be of the order of only 0$\farcs$2, which is close to the effective spatial resolution. They exhibit Doppler shifts of -2 to -4 km s-1 but sometimes up to -7 km s-1, indicating fast upflows. The diameter of a swirl is usually of the order of 2´´. At the location of these swirls, the line wing and wide-band maps show close groups of photospheric bright points that move with respect to each other.
Conclusions. A likely explanation is that the relative motion of the bright points twists the associated magnetic field in the chromosphere above. Plasma or propagating waves may then spiral upwards guided by the magnetic flux structure, thereby producing the observed intensity signature of Doppler-shifted ring fragments.


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



© ESO 2009


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