A comparison of preprocessing methods for solar force-free magnetic field extrapolation

Abstract

Extrapolations of solar photospheric vector magnetograms into three-dimensional magnetic fields in the chromosphere and corona are usually done under the assumption that the fields are force-free. The field calculations can be improved by preprocessing the photospheric magnetograms. We compare two preprocessing methods presently in use, namely the methods of Wiegelmann et al. (2006) and Fuhrmann et al. (2007). The two preprocessing methods were applied to a recently observed vector magnetogram. We examine the changes in the magnetogram effected by the two preprocessing algorithms. Furthermore, the original magnetogram and the two preprocessed magnetograms were each used as input data for nonlinear force-free field extrapolations by means of two different methods, and we analyze the resulting fields. Both preprocessing methods managed to significantly decrease the magnetic forces and magnetic torques that act through the magnetogram area and that can cause incompatibilities with the assumption of force-freeness in the solution domain. Both methods also reduced the amount of small-scale irregularities in the observed photospheric field, which can sharply worsen the quality of the solutions. For the chosen parameter set, the Wiegelmann et al. method led to greater changes in strong-field areas, leaving weak-field areas mostly unchanged, and thus providing an approximation of the magnetic field vector in the chromosphere, while the Fuhrmann et al. method weakly changed the whole magnetogram, thereby better preserving patterns present in the original magnetogram. Both preprocessing methods raised the magnetic energy content of the extrapolated fields to values above the minimum energy, corresponding to the potential field. Also, the fields calculated from the preprocessed magnetograms fulfill the solenoidal condition better than those calculated without preprocessing.

Accepted for Astron. Astrophys

References in corpus (11)

• The Solar Optical Telescope for the Hinode Mission: An Overview
• Optimization code with weighting function for the reconstruction of coronal magnetic fields
• Preprocessing of vector magnetograph data for a non-linear force-free magnetic field reconstruction
• Non-linear force-free field modeling of a solar active region around the time of a major flare and coronal mass ejection
• Nonlinear force-free modeling of the solar coronal magnetic field
• Emergence of a Helical Flux Rope Under an Active Region Prominence
• Computing nonlinear force-free fields in spherical geometry
• Testing magnetofrictional extrapolation with the Titov-Démoulin model of solar active regions
• Can We Improve the Preprocessing of Photospheric Vector Magnetograms by the Inclusion of Chromospheric Observations?
• Nonlinear force-free coronal magnetic field modelling and preprocessing of vector magnetograms in spherical geometry
• Testing non-linear force-free coronal magnetic field extrapolations with the Titov-Demoulin equilibrium

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• Studying the transfer of magnetic helicity in solar active regions with the connectivity-based helicity flux density method
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