Successive X-class Flares and Coronal Mass Ejections Driven by Shearing Motion and Sunspot Rotation in Active Region NOAA 12673

Abstract

We present a clear case study on the occurrence of two successive X-class flares including a decade-class flare (X9.3) and two coronal mass ejections (CMEs) triggered by shearing motion and sunspot rotation in active region NOAA 12673 on 2017 September 6. A shearing motion between the main sunspots with opposite polarities started on September 5 and even lasted after the second X-class flare on September 6. Moreover, the main sunspot with negative polarity rotated around its umbral center and another main sunspot with positive polarity also exhibited a slow rotation. The sunspot with negative polarity at the northwest of active region also began to rotate counter-clockwise before the onset of the first X-class flare, which is related to the formation of the second S-shaped structure. The successive formation and eruption of two S-shaped structures were closely related to the counter-clockwise rotation of three sunspots. The existence of a flux rope is found prior to the onset of two flares by using non-linear force free field extrapolation based on the vector magnetograms observed by SDO/HMI. The first flux rope corresponds to the first S-shaped structures mentioned above. The second S-shaped structure was formed after the eruption of the first flux rope. These results suggest that shearing motion and sunspot rotation play an important role in the buildup of the free energy and the formation of flux ropes in the corona which produces solar flares and CMEs.

CME–CME Interactions as Sources of CME Geoeffectiveness: The Formation of the Complex Ejecta and Intense Geomagnetic Storm in 2017 Early September

“…Démoulin & Pariat 2009;Palmerio et al 2017). In the particular case under study, images in the extreme ultraviolet SDO/AIA filter at 94 Å (Figure 1(g)-(i)) suggest that AR 12673 was characterised by a negative chirality as indicated by the presence of a reverse-S sigmoid in its northern part, which is also consistent with the recent analyses by Mitra et al (2018), Yan et al (2018) and Price et al (2019). Although cases of inconsistency between the chirality of the source region and that of the erupted CME have been observed (e.g.…”

Two Types of Confined Solar Flares

“…All these observations of flare loops or ribbon motions during "type I" confined flares provide the evidence for slipping magnetic reconnections between different sets of magnetic systems. The constant flux emergence and shearing motion (Figure 1) probably help to accumulate the current at the interface between the two systems (Krall et al 1982;Yan et al 2018). Magnetic reconnections could occur within the current layer in the vicinity of QSLs, similar to the simulations of Aulanier et al (2005).…”

Very Fast Helicity Injection Leading to Critically Stable State and Large Eruptive Activity in Solar Active Region NOAA 12673

“…They had proposed a block-induced complex structure for a flare-productive AR. Similarly, Yan et al (2018) suggested the sunspot rotation and shearing motion played an important role in the buildup of free-energy and the formation of flux ropes in the corona which produces solar flares and CMEs. We believe that the long term evolution of the AR has characteristic clues for the nature and strength of the activity, which by studying different AR cases can help constrain the space-weather prediction models.…”