Evaluation of Applicability of a Flare Trigger Model Based on a Comparison of Geometric Structures

Abstract

The triggering mechanism(s) and critical condition(s) of solar flares are still not completely clarified, although various studies have attempted to elucidate them. We have also proposed a theoretical flare-trigger model based on MHD simulations (Kusano et al. 2012), in which two types of small-scale bipole field, the so-called Opposite Polarity (OP) and Reversed Shear (RS) types of field, can trigger flares. In this study, we evaluated the applicability of our flare-trigger model to observation of 32 flares that were observed by the Solar Dynamics Observatory (SDO), by focusing on geometrical structures. We classified the events into six types, including the OP and RS types, based on photospheric magnetic field configuration, presence of precursor brightenings, and shape of the initial flare ribbons. As a result, we found that approximately 30% of the flares were consistent with our flare-trigger model, and the number of RS type triggered flares is larger than that of the OP type. We found none of the sampled events contradicts our flare model, although we cannot clearly determine the trigger mechanism of 70% of the flares in this study. We carefully investigated the applicability of our flare-trigger model and the possibility that other models can explain the other 70% of the events. Consequently, we concluded that our flare-trigger model has certainly proposed important conditions for flare-triggering.

Flare-productive active regions

“…6). From these observations, Bamba et al (2013) suggested that such fine-scale magnetic structures galvanize the whole system into producing flare eruptions (Toriumi et al 2013a;Bamba et al 2017;Bamba and Kusano 2018).…”

An MHD Modeling of Successive X2.2 and X9.3 Solar Flares of 2017 September 6

“…As in this AR, there are several possibilities for eruptions in ARs which have complex magnetic field. Therefore, it is important to detect the disturbance as the triggering process of the solar flare (Bamba et al 2013, Wang et al 2017, Bamba & Kusano 2018, Kang et al 2019 as well as understand the physical property of the 3D magnetic structure (Kusano et al 2020) and also magnetic topology for correctly understanding and predicting. In addition, as a further interesting issue, how difference are large flares produced depending on a reconnection taken place at different area?…”

Intrusion of Magnetic Peninsula toward the Neighboring Opposite-polarity Region That Triggers the Largest Solar Flare in Solar Cycle 24

“…The minimum energy code ME0 (Leka et al 2009a(Leka et al ,b, 2012, which is based on the minimum energy method of Metcalf (1994), was adopted to resolve the 180 • ambiguity in the tangential component of the magnetic fields. As highlighted by Leka et al (2017); Bamba, & Kusano (2018), the three components of the photospheric magnetic field are influenced by a projection-effect; that is, the line-of-sight component of the magnetic field can be treated as the radial component only when the observing angle θ = 0. The AR 12673 was located on September 6, 2017, at S09W42, which is close to the south-east limb.…”

“…Third, the enhanced flare ribbons were extended further south for the X9.3 flare, com-6 We defined precursor brightening as a small brightening intermittently observed at the same site on a magnetic polarity inversion lines where initial flare ribbons appeared on both sides. A physical interpretation of precursor brightening in terms of flare trigger process is discussed in Bamba, & Kusano (2018).…”