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Abstract

American Astronomical Society logo American Astronomical Society logo iop-2016.png iop-2016.png A publishing partnership Toward a Quantitative Comparison of Magnetic Field Extrapolations and Observed Coronal Loops Harry P. Warren1, Nicholas A. Crump1, Ignacio Ugarte-Urra1, Xudong Sun2, Markus J. Aschwanden3, and Thomas Wiegelmann4 Published 2018 June 11 • © 2018. The American Astronomical Society. All rights reserved. The Astrophysical Journal, Volume 860, Number 1 Download Article PDF DownloadArticle ePub Figures Tables References 188 Total downloads 2 2 total citations on Dimensions. Turn on MathJax Get permission to re-use this article Share this article Share this content via email Share on Facebook Share on Twitter Share on Google+ Share on CiteULike Share on Mendeley Article information Abstract It is widely believed that loops observed in the solar atmosphere trace out magnetic field lines. However, the degree to which magnetic field extrapolations yield field lines that actually do follow loops has yet to be studied systematically. In this paper, we apply three different extrapolation techniques—a simple potential model, a nonlinear force-free (NLFF) model based on photospheric vector data, and an NLFF model based on forward fitting magnetic sources with vertical currents—to 15 active regions that span a wide range of magnetic conditions. We use a distance metric to assess how well each of these models is able to match field lines to the 12202 loops traced in coronal images. These distances are typically 1''–2''. We also compute the misalignment angle between each traced loop and the local magnetic field vector, and find values of 5°–12°. We find that the NLFF models generally outperform the potential extrapolation on these metrics, although the differences between the different extrapolations are relatively small. The methodology that we employ for this study suggests a number of ways that both the extrapolations and loop identification can be improved.