Rapid Buildup of a Magnetic Flux Rope during a Confined X2.2 Class Flare in NOAA AR 12673

Abstract

Magnetic flux ropes (MFRs) are believed to be the core structure in solar eruptions, nevertheless, their formation remains intensely debated. Here we report a rapid buildup process of an MFR-system during a confined X2.2 class flare occurred on 2017 September 6 in NOAA AR 12673, three hours after which the structure erupted to a major coronal mass ejection (CME) accompanied by an X9.3 class flare. For the X2.2 flare, we do not find EUV dimmings, separation of its flare ribbons, or clear CME signatures, suggesting a confined flare. For the X9.3 flare, large-scale dimmings, separation of its flare ribbons, and a CME show it to be eruptive. By performing a time sequence of nonlinear force-free fields (NLFFFs) extrapolations we find that: until the eruptive flare, an MFR-system was located in the AR. During the confined flare, the axial flux and the lower bound of the magnetic helicity for the MFR-system were dramatically enhanced by about 86% and 260%, respectively, although the mean twist number was almost unchanged. During the eruptive flare, the three parameters were all significantly reduced. The results evidence the buildup and release of the MFR-system during the confined and the eruptive flare, respectively. The former may be achieved by flare reconnection. We also calculate the pre-flare distributions of the decay index above the main polarity inversion line (PIL) and find no significant difference. It indicates that the buildup of the magnetic flux and helicity of the MFR-system may play a role in facilitating its final eruption.

Time-dependent data-driven coronal simulations of AR 12673 from emergence to eruption

“…it occurred without a CME eruption), while the other one was associated with a CME (e.g. Liu et al 2018;Zou et al 2019). This was a halo CME and had a plane-of-the-sky speed of approximately 1500 km s −1 .…”

“…This active region and its eruptions have been the subject of a number of studies (e.g. Yang et al 2017;Chertok et al 2018;Hou et al 2018;Inoue et al 2018;Liu et al 2018;Verma 2018;Yan et al 2018;Morosan et al 2019;Romano et al 2019;Zou et al 2019). During its transit across the solar disc, this AR produced four GOES X-class flares and numerous weaker flares.…”

Multi-flux-rope system in solar active regions

“…On 2017 September 6, an X9.3 flare took place in AR 12673, which is the largest flare in Solar Cycle 24 (Yang et al 2017;Yan et al 2018;Liu et al 2018). Here we investigate the evolutions of this large flare and the associated complex magnetic system (see more details in Hou et al 2018).…”

“…By examining the AIA 304Å observations, we detected two sets of filament threads located in the AR core region before the occurrence of the X9.3 flare (see F1 and F2 in Fig. 1), which forms a double-decker MFR configuration (Liu et al 2012). Around 11:53:53 UT and 11:54:53 UT, brightenings appeared at the north and south cross sites of these two filament threads (also two MFRs, FR1 and FR2), implying the interaction between rising FR1 and FR2 (see green arrows in panels (a1)-(a2)).…”

Investigation of a Confined C‐Class Flare in an Arch Filament System Close to a Regular Sunspot

“…This lower bound value of the twist is indicative of a weakly twisted, low‐lying, flux rope (Chintzoglou et al, ). In an alternate scenario, flux ropes can also be formed during strong, confined flares quickly leading up to a major CME within a short duration of time (Liu et al, ).…”