Effect of the Size of the Computational Domain on Spherical Nonlinear Force-Free Modeling of a Coronal Magnetic Field Using SDO/HMI Data

Abstract

The solar coronal magnetic field produces solar activity, including extremely energetic solar flares and coronal mass ejections (CMEs). Knowledge of the structure and evolution of the magnetic field of the solar corona is important for investigating and understanding the origins of space weather. Although the coronal field remains difficult to measure directly, there is considerable interest in accurate modeling of magnetic fields in and around sunspot regions on the Sun using photospheric vector magnetograms as boundary data. In this work, we investigate effects of the size of the domain chosen for coronal magnetic field modeling on resulting model solutions. We applied a spherical nonlinear force-free optimization procedure to vector magnetogram data of the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). We selected a particular observation in which there were four active regions observed on 9 March 2012 at 20:55 UT. The results imply that quantities such as magnetic flux density, electric current density, and free magnetic energy density of active regions of interest are significantly different from the corresponding quantities obtained in the same region with a larger computational domain. The difference is even more pronounced in the regions that are connected to the outside of the domain.