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| Titel |
Computing nonlinear force free coronal magnetic fields |
| VerfasserIn |
T. Wiegelmann, T. Neukirch |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1023-5809
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| Digitales Dokument |
URL |
| Erschienen |
In: Nonlinear Processes in Geophysics ; 10, no. 4/5 ; Nr. 10, no. 4/5, S.313-322 |
| Datensatznummer |
250007832
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| Publikation (Nr.) |
 copernicus.org/npg-10-313-2003.pdf |
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| Zusammenfassung |
| Knowledge of the
structure of the coronal magnetic field is important for our understanding
of many solar activity phenomena, e.g. flares and CMEs. However, the
direct measurement of coronal magnetic fields is not possible with present
methods, and therefore the coronal field has to be extrapolated from
photospheric measurements. Due to the low plasma beta the coronal magnetic
field can usually be assumed to be approximately force free, with electric
currents flowing along the magnetic field lines. There are both
observational and theoretical reasons which suggest that at least prior to
an eruption the coronal magnetic field is in a nonlinear force free state.
Unfortunately the computation of nonlinear force free fields is way more
difficult than potential or linear force free fields and analytic
solutions are not generally available. We discuss several methods which
have been proposed to compute nonlinear force free fields and focus
particularly on an optimization method which has been suggested recently.
We compare the numerical performance of a newly developed numerical code
based on the optimization method with the performance of another code
based on an MHD relaxation method if both codes are applied to the
reconstruction of a semi-analytic nonlinear force-free solution. The
optimization method has also been tested for cases where we add random
noise to the perfect boundary conditions of the analytic solution, in this
way mimicking the more realistic case where the boundary conditions are
given by vector magnetogram data. We find that the convergence properties
of the optimization method are affected by adding noise to the boundary
data and we discuss possibilities to overcome this difficulty. |
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