Structure and Stability of Magnetic Fields in Solar Active Region12192 Based on Nonlinear Force-Free Field Modeling

TL;DR

This study models the 3D magnetic structure of solar active region 12192 using nonlinear force-free field approximation, revealing complex flux tube systems, stability features, and potential flare ribbon shapes related to an X3.1-class solar flare.

Contribution

It provides a detailed 3D magnetic field analysis of AR 12192, highlighting the coexistence of multiple flux tubes and their stability, which advances understanding of flare mechanisms without major eruptions.

Findings

Multiple flux tubes coexist in AR 12192.

Most magnetic twists remain after the flare.

Upper flux tube exceeds decay index for torus instability.

Abstract

We analyze a three-dimensional (3D) magnetic structure and its stability in large solar active region(AR) 12192, using the 3D coronal magnetic field constructed under a nonlinear force-free field (NLFFF) approximation. In particular, we focus on the magnetic structure that produced an X3.1-class flare which is one of the X-class flares observed in AR 12192. According to our analysis, the AR contains multiple-flux-tube system, {\it e.g.}, a large flux tube, both of whose footpoints are anchored to the large bipole field, under which other tubes exist close to a polarity inversion line (PIL). These various flux tubes of different sizes and shapes coexist there. In particular, the later are embedded along the PIL, which produces a favorable shape for the tether-cutting reconnection and is related to the X-class solar flare. We further found that most of magnetic twists are not released even after the flare, which is consistent with the fact that no observational evidence for major eruptions was found. On the other hand, the upper part of the flux tube is beyond a critical decay index, essential for the excitation of torus instability before the flare, even though no coronal mass ejections (CMEs) were observed. We discuss the stability of the complicated flux tube system and suggest the reason for the existence of the stable flux tube. In addition, we further point out a possibility for tracing the shape of flare ribbons, on the basis of a detailed structural analysis of the NLFFF before a flare.