Comparing magnetic field extrapolations with measurements of magnetic loops

TL;DR

This study evaluates different magnetic field extrapolation methods by comparing them with actual magnetic loop observations in a new active region, highlighting the superiority of non-linear force-free models.

Contribution

First comparison of 3D magnetic field reconstructions with observed loops in a developing active region, demonstrating the effectiveness of non-linear force-free extrapolations.

Findings

Potential fields are inadequate for young active regions.

Force-free models improve reconstruction accuracy.

Non-linear force-free fields outperform linear models.

Abstract

We compare magnetic field extrapolations from a photospheric magnetogram with the observationally inferred structure of magnetic loops in a newly developed active region. This is the first time that the reconstructed 3D-topology of the magnetic field is available to test the extrapolations. We compare the observations with potential fields, linear force-free fields and non-linear force-free fields. This comparison reveals that a potential field extrapolation is not suitable for a reconstruction of the magnetic field in this young, developing active region. The inclusion of field-line-parallel electric currents, the so called force-free approach, gives much better results. Furthermore, a non-linear force-free computation reproduces the observations better than the linear force-free approximation, although no free parameters are available in the former case.