Preprocessing of Hinode/SOT vector magnetograms for nonlinear force-free coronal magnetic field modelling

TL;DR

This paper presents a preprocessing method to transform Hinode/SOT vector magnetogram data into a form suitable for nonlinear force-free coronal magnetic field modeling, addressing the non-force-free nature of photospheric measurements.

Contribution

The authors developed and tested a minimization preprocessing procedure that adjusts photospheric magnetic data to better approximate chromospheric conditions for accurate extrapolation.

Findings

Preprocessing improves force-free consistency of magnetogram data.

Method successfully applied to Hinode/SOT measurements.

Enhances the reliability of coronal magnetic field models.

Abstract

The solar magnetic field is key to understanding the physical processes in the solar atmosphere. Nonlinear force-free codes have been shown to be useful in extrapolating the coronal field from underlying vector boundary data [see Schrijver et al. 2006 for an overview]. However, we can only measure the magnetic field vector routinely with high accuracy in the photosphere with, e.g., Hinode/SOT, and unfortunately these data do not fulfill the force-free consistency condition as defined by Aly (1989). We must therefore apply some transformations to these data before nonlinear force-free extrapolation codes can be legitimately applied. To this end, we have developed a minimization procedure that uses the measured photospheric field vectors as input to approximate a more chromospheric like field The method was dubbed preprocessing. See Wiegelmann et al. 2006 for details]. The procedure includes force-free consistency integrals and spatial smoothing. The method has been intensively tested with model active regions [see Metcalf et al. 2008] and been applied to several ground based vector magnetogram data before. Here we apply the preprocessing program to photospheric magnetic field measurements with the Hinode/SOT instrument.