Non-constant-alpha force-free reconstruction of the coronal magnetic field. Example of the active region NOAA 8151

Details Non-constant-alpha force-free reconstruction of the coronal magnetic field. Example of the active region NOAA 8151 Non-constant-alpha force-free reconstruction of the coronal magnetic field. Example of the active region NOAA 8151

Dec 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufmsh11c0729r&link_type=abstract

American Geophysical Union, Fall Meeting 2001, abstract #SH11C-0729

Mathematics

Logic

7509 Corona, 7524 Magnetic Fields

Scientific paper

We present the method and results of a non-constant-alpha force-free reconstruction of the 3D coronal magnetic field of an active region. AR 8151 observed in February 1998 exhibits a filament, a system of coronal loops, and a sigmoid. In order to determine the magnetic configuration of such structures, a non-constant-alpha force-free method (Amari et al 1997, Solar Physics 174, 129) is used to reconstruct the coronal magnetic field using the photospheric vector magnetograms as boundary condition. We compare the geometric and the topological changes in the magnetic configurations given by the three following methods: current-free field, constant-alpha force-free field and non-constant-alpha force-free field. The comparison between the observations (SXT/Yohkoh, EIT/SOHO) and the three models confirms that the non-constant-alpha force-free field matches the observations. In particular, the sigmoid can be reproduced by twisted flux tubes with a height of 40,000 or 60,000 km, and the system of coronal loops is well described by an untwisted flux tube (40,000 km). We also look for the magnetic dips which are combined with the filament material. The possible magnetic configurations for supporting the filament are either a quadrupolar magnetic field or a long twisted flux tube. From the chromospheric and magnetic observations, we conclude that the most likely configuration is the long twisted flux tube with a height of 30,000 km. In summary, with the non-constant-alpha force-free field we are able to reconstruct the coronal magnetic structures such as the system of coronal loops and the sigmoid, and to determine the structure of the magnetic field lines supporting the filament material.

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