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Testing the alphabest magnetic field extrapolation method with nonlinear force-free fields View all abstracts by submitter

Bernhard Kliem   Submitted: 2004-12-15 15:38

We apply the alphabest magnetic field extrapolation method to two complementary nonlinear force-free models of solar active regions containing a twisted flux rope, in order to demonstrate that the method strongly underestimates the current helicity density in equilibrium flux ropes with twists exceeding Phisimpi. This behaviour results from the limit set on the force-free parameter α by the employed linear force-free field and from the compromise in fitting a linear to a nonlinear force-free field embodied by the method. The result holds for flux ropes with and without a net current. The α _mathrm{best} values obtained for nonlinear fields scatter strongly if the magnetogram size or the threshold field strength used in determining α _mathrm{best} are varied. The scatter can, in some cases, even lead to a sign of α _mathrm{best} opposite to that of α in the core of the flux rope.

Authors: B. Kliem and G. Valori
Projects: None

Publication Status: ApJ, submitted
Last Modified: 2004-12-15 15:38
Go to main E-Print page  Early signatures of large-scale field line opening  Multi-wavelength analysis of features connected with a 'halo' CME event  Extrapolation of a nonlinear force-free field containing a highly twisted magnetic loop  Edit Entry  Download Preprint  Submitter's Homepage Delete Entry 

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