The Magnetic Topology and Eruption Mechanism of a Multiple-ribbon Flare

TL;DR

This paper investigates the magnetic topology and eruption mechanism of a complex X2.1 solar flare, revealing the role of flux ropes, hyperbolic flux tubes, and null points in the flare's development and associated CME.

Contribution

It provides a detailed magnetic topology analysis of a multiple-ribbon flare using advanced modeling and simulations, highlighting the flux ropes and HFT structures involved.

Findings

Identification of two flux ropes and a hyperbolic flux tube in the active region.

The flux rope's rise triggers brightening and CME acceleration.

The CME's early acceleration profile fits a 45-degree inclination path.

Abstract

Multiple-ribbon flares are usually complex in their magnetic topologies and eruption mechanisms. In this paper, we investigate an X2.1 flare (SOL2015-03-11T16:22) that occurred in active region 12297 near the center of the solar disk by both potential and nonlinear force-free field models extrapolated with the data observed by the Helioseismic and Magnetic Imager (HMI) on board Solar Dynamics Observatory (SDO). We calculate the three-dimensional squashing degree distribution. The results reveal that there are two flux ropes in this active region, covered by a large scale hyperbolic flux tube (HFT), which is the intersection of quasi-separatrix layers with a null point embedded in it. When the background magnetic field diminishes due to the separation of the northwest dipole and the flux cancellation, the central flux rope rises up forming the two brightest central ribbons. It then squeezes the upper lying HFT structure to generate further brightenings. This very energetic flare with a complex shape is accompanied by a coronal mass ejection (CME). We adopt the simplified line-tied force-balance equation of the current ring model and assign the observed value of the decay index to the equation to simulate the acceleration profile of the CME in the early stage. It is found that the path with an inclination of $45^\circ$ from radial best fits the profile of the actual acceleration.