Transient downflows associated with the intensification of small-scale magnetic features and bright point formation⋆
Institute for Solar Physics, Royal Swedish Academy of Sciences, AlbaNova University Center, 106 91 Stockholm, Sweden
2 Stockholm Observatory, Dept. of Astronomy, Stockholm University, AlbaNova University Center, 106 91 Stockholm, Sweden
Received: 28 October 2010
Accepted: 31 January 2011
Context. Small-scale magnetic features are present everywhere in the solar photosphere. Theoretical models, numerical calculations, and simulations describing the formation of these features have existed for a few decades, but there are only a few observational studies in direct support of the simulations. In particular, there is a lack of high resolution spectropolarimetric observations capturing the formation of small-scale magnetic features.
Aims. In this study we present the evolution of small-scale magnetic features with a spatial resolution close to 015 and compare these observations with those predicted by numerical simulations and also with previous observational work of a similar nature.
Methods. We analyze a 40 min time sequence of full Stokes spectropolarimetric 630.25 nm data from a plage region near the Sun center. We use line-of-sight velocities and magnetic field measurements obtained using Milne-Eddington inversion techniques with and without stray-light compensation along with measured continuum and line minimum intensities. We discuss the results in relation to earlier observations and simulations.
Results. We present eight cases involving strong transient downflows and magnetic field intensification. All cases studied are associated with the formation of a bright point in the continuum. In three out of the eight cases we find the presence of weak opposite polarity field in close proximity to the downflow.
Conclusions. Our data are consistent with earlier simulations describing flux tube collapse, but the transition to a state with stronger field appears transient and short-lived, rather than resulting in a permanent field intensification. Three cases of weak opposite polarity field found adjacent to the downflows do not appear related to reconnection but may be related to overturning convection pulling down some field lines and leading to up/down “serpentine”field, as seen in some simulations.
Key words: Sun: photosphere / Sun: granulation / Sun: faculae, plages / Sun: surface magnetism
Appendix A is only available in electronic form at http://www.aanda.org
© ESO, 2011