Nonlinear Force-Free Modeling of Coronal Magnetic Fields. II. Modeling a Filament Arcade and Simulated Chromospheric and Photospheric Vector Fields

By T. Metcalf, M. DeRosa, C. Schrijver, G. Barnes, A. A. Ballegooijen, T. Wiegelmann, M. Wheatland, G. Valori, James M. McTtiernan. 2008

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We compare a variety of nonlinear force-free field (NLFFF) extrapolation algorithms, including optimization, magneto-frictional, and Grad – Rubin-like codes, applied to a solar-like reference model. The model used to test the algorithms includes realistic photospheric Lorentz forces and a complex field including a weakly twisted, right helical flux bundle. The codes were applied to both forced “photospheric” and more force-free “chromospheric” vector magnetic field boundary data derived from the model. When applied to the chromospheric boundary data, the codes are able to recover the presence of the flux bundle and the field’s free energy, though some details of the field connectivity are lost. When the codes are applied to the forced photospheric boundary data, the reference model field is not well recovered, indicating that the combination of Lorentz forces and small spatial scale structure at the photosphere severely impact the extrapolation of the field. Preprocessing of the forced photospheric boundary does improve the extrapolations considerably for the layers above the chromosphere, but the extrapolations are sensitive to the details of the numerical codes and neither the field connectivity nor the free magnetic energy in the full volume are well recovered. The magnetic virial theorem gives a rapid measure of the total magnetic energy without extrapolation though, like the NLFFF codes, it is sensitive to the Lorentz forces in the coronal volume. Both the magnetic virial theorem and the Wiegelmann extrapolation, when applied to the preprocessed photospheric boundary, give a magnetic energy which is nearly equivalent to the value derived from the chromospheric boundary, but both underestimate the free energy above the photosphere by at least a factor of two. We discuss the interpretation of the preprocessed field in this context. When applying the NLFFF codes to solar data, the problems associated with Lorentz forces present in the low solar atmosphere must be recognized: the various codes will not necessarily converge to the correct, or even the same, solution.

Subfields: Astronomy and Astrophysics, Molecular Biology

View Paper: https://www.semanticscholar.org/paper/8f4acc42ca2da0ab499d4a8850068f970e2835e8

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Citations in the corpus

Tracking Vector Magnetograms with the Magnetic Induction Equation (2008, methodology): “To address this Metcalf et al. (2008) suggested weighting the errors.”
GLOBAL ENERGETICS OF THIRTY-EIGHT LARGE SOLAR ERUPTIVE EVENTS (2012, background): “Published values for free energies in analytic (Schrijver et al. 2006) and semi-empirical (Metcalf et al. 2008) fields meant to model solar fields also hover around a few tens of percent of the potential field energy.”
COEXISTING FLUX ROPE AND DIPPED ARCADE SECTIONS ALONG ONE SOLAR FILAMENT (2010, methodology): “…the extrapolation domain (Wheatland et al. 2000), and it is 5.0 × 10−4 for the extrapolation of preprocessed and smoothed photospheric data generated by the flux rope insertion method (van Ballegooijen et al. 2000; van Ballegooijen 2004), using the optimization method (Metcalf et al. 2008).”
EVOLUTION OF MAGNETIC FIELD AND ENERGY IN A MAJOR ERUPTIVE ACTIVE REGION BASED ON SDO/HMI OBSERVATION (2011, background): “If the boundary is force-free enough and the region is largely isolated, as is the case for this HMI time series (see Appendix A), the free energy in the volume is expected to be well recovered (Metcalf et al. 2008).”
The magnetic field in the solar atmosphere (2014, background): “The corresponding numerical implementations have been intensively reviewed, and repeatedly evaluated and improved within the last decade (see Schrijver et al. 2006; Metcalf et al. 2008; Schrijver et al. 2008; De Rosa et al. 2009).”
How Should One Optimize Nonlinear Force-Free Coronal Magnetic Field Extrapolations from SDO/HMI Vector Magnetograms? (2012, background): “For reviews see (Sakurai, 1989; Aly, 1989; Amari et al., 1997; Wiegelmann, 2008) and within the last few years the different numerical codes have been intensively tested, evaluated and compared in (Schrijver et al., 2006; Metcalf et al., 2008; Schrijver et al., 2008).”
A CRITICAL ASSESSMENT OF NONLINEAR FORCE-FREE FIELD MODELING OF THE SOLAR CORONA FOR ACTIVE REGION 10953 (2009, background): “The previous results from this collaboration are presented in Schrijver et al. (2006), Metcalf et al. (2008), and Schrijver et al. (2008).”
Driving major solar flares and eruptions: A review (2008, methodology): “An application of the virial theorem to a model field in the detailed study by Metcalf et al. (2008), for example, shows that the magnitude of the uncertainty in the virial-theorem estimate of free energy is comparable to that in NLFF models.”