Nonlinear Force-Free Magnetic Field Fitting to Coronal Loops with and without Stereoscopy

TL;DR

This paper introduces a new NLFFF forward-fitting algorithm that accurately models coronal magnetic fields using only 2D loop data, eliminating the need for stereoscopic observations, and demonstrates its effectiveness on simulated and real data.

Contribution

The authors developed a fast, accurate NLFFF fitting method that works with 2D loop data, reducing reliance on stereoscopy for active region magnetic modeling.

Findings

NLFFF solutions can be fitted with or without stereoscopy with similar accuracy.

The 2D loop tracing achieves a misalignment of about 2.7 degrees.

The method accurately estimates magnetic energy ratios within 1%."],

Abstract

We developed a new nonlinear force-free magnetic field (NLFFF) forward-fitting algorithm based on an analytical approximation of force-free and divergence-free NLFFF solutions, which requires as input a line-of-sight magnetogram and traced 2D loop coordinates of coronal loops only, in contrast to stereoscopically triangulated 3D loop coordinates used in previous studies. Test results of simulated magnetic configurations and from four active regions observed with STEREO demonstrate that NLFFF solutions can be fitted with equal accuracy with or without stereoscopy, which relinquishes the necessity of STEREO data for magnetic modeling of active regions (on the solar disk). The 2D loop tracing method achieves a 2D misalignment of $\mu_2=2.7^\circ\pm 1.3^\circ$ between the model field lines and observed loops, and an accuracy of $\approx 1.0%$ for the magnetic energy or free magnetic energy ratio. The three times higher spatial resolution of TRACE or SDO/AIA (compared with STEREO) yields also a proportionally smaller misalignment angle between model fit and observations. Visual/manual loop tracings are found to produce more accurate magnetic model fits than automated tracing algorithms. The computation time of the new forward-fitting code amounts to a few minutes per active region.