Volume 524, December 2010
|Number of page(s)||9|
|Published online||19 November 2010|
A new type of small-scale downflow patches in sunspot penumbrae
National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo
2 Astronomical Institute of the Academy of Sciences, Fricova 298, 25165 Ondřejov, Czech Republic
Accepted: 9 July 2010
Context. Magnetic and flow structures in a sunspot penumbra are created by strong interplay between inclined magnetic fields and photospheric convection. They exhibit a complex nature that cannot always be explained by the well-known Evershed flow.
Aims. A sunspot penumbra is observationally examined to reveal properties of small-scale flow structures and their relationship to the filamentary magnetic structures and the Evershed flow. We also study how the photospheric dynamics are related to chromospheric activities.
Methods. This study is based on data analysis of spectro-polarimetric observations of photospheric Fe I lines with the Solar Optical Telescope aboard Hinode in a sunspot penumbra at different heliocentric angles. Vector magnetic fields and velocities are derived using the spectro-polarimetric data and a Stokes inversion technique. An observation with a Ca II H filtergram co-spatial and co-temporal with the spectro-polarimetric one is also used to study possible chromospheric responses.
Results. We find small patches with downflows in the photospheric layers. The downflow patches have a size of 0.5′′ or smaller and a different geometrical configuration from the Evershed flow. The downflow velocity is about 1 km s-1 in the lower photspheric layers and is almost zero in the upper layers. Some of the downflow patches are associated with brightenings seen in Ca II H images.
Conclusions. The downflows are possible observational signatures of downward flows driven by magnetic reconnection in the interlaced magnetic field configuration, where upward flows make brightenings in the chromosphere. Another possibility is that they are concentrated downward flows of overturning magnetoconvection.
Key words: Sun: chromosphere / Sun: photosphere / Sun: surface magnetism / sunspots
© ESO, 2010
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