Magnetic Properties of Solar Active Regions That Govern Large Solar Flares and Eruptions

Abstract

Solar flares and coronal mass ejections (CMEs), especially the larger ones, emanate from active regions (ARs). With the aim to understand the magnetic properties that govern such flares and eruptions, we systematically survey all flare events with GOES levels of ≥ M5.0 within 45• from disk center between May 2010 and April 2016. These criteria lead to a total of 51 flares from 29 ARs, for which we analyze the observational data obtained by the Solar Dynamics Observatory. More than 80% of the 29 ARs are found to exhibit δ-sunspots and at least three ARs violate Hale's polarity rule. The flare durations are approximately proportional to the distance between the two flare ribbons, to the total magnetic flux inside the ribbons, and to the ribbon area. From our study, one of the parameters that clearly determine whether a given flare event is CME-eruptive or not is the ribbon area normalized by the sunspot area, which may indicate that the structural relationship between the flaring region and the entire AR controls CME productivity. AR characterization show that even X-class events do not require δ-sunspots or strong-field, high-gradient polarity inversion lines. An investigation of historical observational data suggests the possibility that the largest solar ARs, with magnetic flux of 2×10 23 Mx, might be able to produce "superflares" with energies of order of 10 34 erg. The proportionality between the flare durations and magnetic energies is consistent with stellar flare observations, suggesting a common physical background for solar and stellar flares.

On the Factors Determining the Eruptive Character of Solar Flares

“…Fig. 6 of Toriumi et al 2017). That means that they originated from a minor ("satellite") bipolar magnetic flux concentration located in the periphery of an AR.…”

“…Out of these, 12 (∼27%) events were confined (7 M-and 5 X-flares) and 32 (∼73%) were eruptive (18 M-and 14 X-flares). In comparison to Toriumi et al (2017), we classify two events differently. Firstly, we classify event no.…”

Testing predictors of eruptivity using parametric flux emergence simulations

“…Given our framework, our study is thus limited in terms of size and complexity of active regions that we cannot explore: the reliability of eruptive indicators is tested only for a given class of active region size and complexity. Nonetheless, it is worth noting that a recent study by Toriumi et al (2017) concludes that a complex d-sunspot is not a necessary condition for flaring ARs, even for the X-class flares. Thus, this kind of controlled study is important in the sense that the size and the complexity of an active region are not discriminant parameters for eruptivity: small active regions can still produce flares, while two active regions in the same size and complexity range do not necessarily have the same flaring likelihood.…”

“…Determining whether or not the net electric current I AE net is neutralized over individual polarities of ARs is crucial for some theoretical flare and CMEs models (e.g., Melrose 1991;Parker 1996;Titov & Démoulin 1999;Forbes 2010). If the AR currents are fully neutralized, the net current integrated over one photospheric polarity is set to zero.…”

Observation of a Large-scale Quasi-circular Secondary Ribbon Associated with Successive Flares and a Halo CME

“…Recent statistical study of flare ribbons by Toriumi et al (2017) demonstrated that compared to confined flares, the eruptive flares showed a larger ratio of the ribbon area to AR area. According to the authors, this ratio reflects the relative scale of the magnetic field involved in reconnection compared to the ambient field that is an obstacle for fast and powerful eruption.…”