EDP Sciences
Free access
Volume 442, Number 1, October IV 2005
Page(s) 351 - 358
Section The Sun
DOI http://dx.doi.org/10.1051/0004-6361:20042016

A&A 442, 351-358 (2005)
DOI: 10.1051/0004-6361:20042016

On the 3-dimensional structure of the streamer belt of the solar corona

F. Saez1, A. N. Zhukov2, 3, P. Lamy1 and A. Llebaria1

1  Laboratoire d'Astronomie Spatiale (CNRS) Les Trois Lucs, BP 8, 13376 Marseille Cedex 12, France
    e-mail: fabien.saez@oamp.fr
2  Royal Observatory of Belgium, Avenue Circulaire 3, 1180 Brussels, Belgium
3  Skobeltsyn Institute of Nuclear Physics, Moscow State University, 119992 Moscow, Russia

(Received 15 September 2004 / Accepted 5 July 2005 )

We investigate the three-dimensional structure of the streamer belt of the solar corona using a model that allows us to simulate its quasi-stationary configuration. Starting from the National Solar Observatory photospheric magnetograms, the position of the neutral line at the source surface ( $2.5 ~R_\odot$) is determined using the potential field source surface model. A plasma sheet is centered around the current sheet represented as the radial extension of the neutral line. Comparing the synoptic maps of the streamer belt obtained with the SOHO/LASCO-C2 coronagraph and the simulated synoptic maps constructed from our model of the warped plasma sheet, we confirm earlier findings by Wang et al. (1997, ApJ, 485, 875; Wang et al. 2000, Geophys. Res. Lett., 27, 149) that the streamers are associated with folds in the plasma sheet. Although the large-scale structure of the streamer belt is described reasonably well, some features, however, cannot be explained in this framework. We propose that two types of large-scale structures take part in the formation of these additional features. The first one is an additional fold of the neutral line, which does not appear in the modeled source surface neutral line, but is well visible in photospheric magnetograms. The second one is a plasma sheet with a ramification in the form of a secondary short plasma sheet. We show that these structures better describe the observed configurations of the streamer belt. The secondary plasma sheet can be formed between two secondary current sheets connected to the main current sheet. Our results suggest that the potential field source surface model is not fully adequate for the description of the fine structure of the streamer belt, even during the time of low solar activity.

Key words: Sun: corona -- Sun: magnetic fields

© ESO 2005