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First 3D Reconstructions of Coronal Loops with the STEREO A+B Spacecraft: IV. Magnetic Modeling with Twisted Force-Free Fields View all abstracts by submitter

Markus J. Aschwanden   Submitted: 2012-07-11 14:09

The three-dimensional (3D) coordinates of stereoscopically triangulated loops provide strong constraints for magnetic field models of active regions in the solar corona. Here we use STEREO/A and B data from some 500 stereoscopically triangulated loops observed in four active regions (2007 Apr 30, May 9, May 19, Dec 11), together with SOHO/MDI line-of-sight magnetograms. We measure the average misalignment angle between the stereoscopic loops and theoretical magnetic field models, finding a mismatch of mu=19°-46° for a potential field model, which is reduced to mu=14°-19° for a non-potential field model parameterized by twist parameters. The residual error is commensurable with stereoscopic measurement errors (muSE approx 8°-12°). We developed a potential field code that deconvolves a line-of-sight magnetogram into three magnetic field components (B_x, B_y, B_z), as well as a non-potential field forward-fitting code that determines the full length of twisted loops (L approx 50-300 Mm), the number of twist turns (median Ntwist=0.06), the nonlinear force-free α -parameter (median α approx 4 imes 10-11 cm-1), and the current density (median j_z approx 1500 Mx cm-2 s-1). All twisted loops are found to be far below the critical value for kink instability, and Joule dissipation of their currents is found be be far below the coronal heating requirement. The algorithm developed here, based on an analytical solution of nonlinear force-free fields that is accurate to second order (in the force-free parameter α ), represents the first code that enables fast forward-fitting to photospheric magnetograms and stereoscopically triangulated loops in the solar corona.

Authors: Markus J. Aschwanden, Jean-Pierre Wuelser, Nariaki V. Nitta, James R. Lemen, Marc L. DeRosa, and Anna Malanushenko
Projects: STEREO

Publication Status: The Astrophysical Journal (in press)
Last Modified: 2012-07-12 09:38
Go to main E-Print page  Solar Stereoscopy with STEREO/EUVI A and B spacecraft from small (6°) to large (170°) spacecraft separation angles  A Nonlinear Force-Free Magnetic Field Approximation         Suitable for Fast Forward-Fitting to Coronal Loops.  II. Numeric Code and Tests  Edit Entry  Download Preprint  Submitter's Homepage Delete Entry 

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