Study of the 3D Coronal Magnetic Field of Active Region 11117 Around the Time of a Confined Flare Using a Data-Driven CESE--MHD Model

TL;DR

This study uses a data-driven MHD model to analyze the 3D magnetic field of NOAA AR 11117 around a confined C-class flare, revealing magnetic topology and energy changes associated with the flare.

Contribution

It introduces a data-driven CESE--MHD model that reproduces the coronal magnetic field structure and links magnetic reconnection at a bald patch to flare energy release.

Findings

The model qualitatively matches observed coronal loops.

Magnetic free energy decreases by ~10^30 erg during the flare.

Magnetic topology indicates reconnection at a bald patch.

Abstract

We apply a data-driven MHD model to investigate the three-dimensional (3D) magnetic field of NOAA active region (AR) 11117 around the time of a C-class confined flare occurred on 2010 October 25. The MHD model, based on the spacetime conservation-element and solution-element (CESE) scheme, is designed to focus on the magnetic-field evolution and to consider a simplified solar atomsphere with finite plasma $\beta$. Magnetic vector-field data derived from the observations at the photoshpere is inputted directly to constrain the model. Assuming that the dynamic evolution of the coronal magnetic field can be approximated by successive equilibria, we solve a time sequence of MHD equilibria basing on a set of vector magnetograms for AR 11117 taken by the Helioseismic and Magnetic Imager (HMI) on board the {\it Solar Dynamic Observatory (SDO)} around the time of flare. The model qualitatively reproduces the basic structures of the 3D magnetic field, as supported by the visual similarity between the field lines and the coronal loops observed by the Atmospheric Imaging Assembly (AIA), which shows that the coronal field can indeed be well characterized by the MHD equilibrium in most time. The magnetic configuration changes very limited during the studied time interval of two hours. A topological analysis reveals that the small flare is correlated with a bald patch (BP, where the magnetic field is tangent to the photoshpere), suggesting that the energy release of the flare can be understood by magnetic reconnection associated with the BP separatrices. The total magnetic flux and energy keep increasing slightly in spite of the flare, while the computed magnetic free energy drops during the flare with an amount of $\sim 10^{30}$ erg, which seems to be adequate to provide the energy budget of the minor C-class confined flare.