Full-disk nonlinear force-free field extrapolation of SDO/HMI and SOLIS/VSM magnetograms

TL;DR

This paper develops a full-disk nonlinear force-free field extrapolation method in spherical coordinates to model the Sun's coronal magnetic field using SDO/HMI and SOLIS/VSM data, enabling analysis of entire solar disks.

Contribution

It introduces a spherical geometry extrapolation code for full-disk magnetic field modeling, improving upon previous Cartesian methods limited to small areas.

Findings

Good agreement between HMI and VSM extrapolated magnetic field lines

HMI data yields higher magnetic energy and current densities than VSM data

Full-disk modeling captures large-scale solar magnetic structures

Abstract

Extrapolation codes in Cartesian geometry for modelling the magnetic field in the corona do not take the curvature of the Sun's surface into account and can only be applied to relatively small areas, e.g., a single active region. We compare the analysis of the photospheric magnetic field and subsequent force-free modeling based on full-disk vector maps from Helioseismic and Magnetic Imager (HMI) on board solar dynamics observatory (SDO) and Vector Spectromagnetograph (VSM) of the Synoptic Optical Long-term Investigations of the Sun (SOLIS). We use Helioseismic and Magnetic Imager and Vector Spectromagnetograph photospheric magnetic field measurements to model the force-free coronal field above multiple solar active regions, assuming magnetic forces to dominate. We solve the nonlinear force-free field equations by minimizing a functional in spherical coordinates over a full disk excluding the poles. After searching for the optimum modeling parameters for the particular data sets, we compare the resulting nonlinear force-free model fields. We compare quantities like the total magnetic energy content and free magnetic energy, the longitudinal distribution of the magnetic pressure and surface electric current density using our spherical geometry extrapolation code. The magnetic field lines obtained from nonlinear force-free extrapolation based on Helioseismic and Magnetic Imager and Vector Spectromagnetograph data have good agreement. However, the nonlinear force-free extrapolation based on Helioseismic and Magnetic Imager data have more contents of total magnetic energy, free magnetic energy, the longitudinal distribution of the magnetic pressure and surface electric current density compared to the one from Vector Spectromagnetograph data.