Eruption of a multi-flux-rope system in solar active region 12673 leading to the two largest flares in Solar Cycle 24

TL;DR

This paper investigates the complex magnetic flux rope system in solar active region 12673 that led to the two largest flares of Solar Cycle 24, revealing the magnetic evolution and eruption mechanisms involved.

Contribution

It provides a detailed analysis of the multi-flux-rope system and its role in major solar flares, using NLFFF modeling and magnetic field evolution data.

Findings

Double-decker flux rope configuration identified in AR 12673.

Magnetic flux emergence and dipole interactions contributed to flare eruptions.

Sequential eruptions suggest chain-reaction magnetic destabilization.

Abstract

Solar active region (AR) 12673 in 2017 September produced two largest flares in Solar Cycle 24: the X9.3 flare on September 06 and the X8.2 flare on September 10. We attempt to investigate the evolutions of the two great flares and their associated complex magnetic system in detail. Aided by the NLFFF modeling, we identify a double-decker flux rope configuration above the polarity inversion line (PIL) in the AR core region. The north ends of these two flux ropes were rooted in a negative- polarity magnetic patch, which began to move along the PIL and rotate anticlockwise before the X9.3 flare on September 06. The strong shearing motion and rotation contributed to the destabilization of the two magnetic flux ropes, of which the upper one subsequently erupted upward due to the kink-instability. Then another two sets of twisted loop bundles beside these ropes were disturbed and successively erupted within 5 minutes like a chain reaction. Similarly, multiple ejecta components were detected to consecutively erupt during the X8.2 flare occurring in the same AR on September 10. We examine the evolution of the AR magnetic fields from September 03 to 06 and find that five dipoles emerged successively at the east of the main sunspot. The interactions between these dipoles took place continuously, accompanied by magnetic flux cancellations and strong shearing motions. In AR 12673, significant flux emergence and successive interactions between the different emerging dipoles resulted in a complex magnetic system, accompanied by the formations of multiple flux ropes and twisted loop bundles. We propose that the eruptions of a multi-flux-rope system resulted in the two largest flares in Solar Cycle 24.