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.
@article{arxiv.0801.4519,
title = {Comparing magnetic field extrapolations with measurements of magnetic loops},
author = {T. Wiegelmann and A. Lagg and S. K. Solanki and B. Inhester and J. Woch},
journal= {arXiv preprint arXiv:0801.4519},
year = {2009}
}