The Magnetic Systems Triggering the M6.6 Class Solar Flare in Noaa Active Region 11158

Abstract

We report a detailed event analysis on the M6.6-class flare in the active region (AR) NOAA 11158 on 2011 February 13. AR 11158, which consisted of two major emerging bipoles, showed prominent activities including one X-and several M-class flares. In order to investigate the magnetic structures related to the M6.6 event, particularly the formation process of a flare-triggering magnetic region, we analyzed multiple spacecraft observations and numerical results of a flare simulation. We observed that, in the center of this quadrupolar AR, a highly sheared polarity inversion line (PIL) was formed through proper motions of the major magnetic elements, which built a sheared coronal arcade lying over the PIL. The observations lend support to the interpretation that the target flare was triggered by a localized magnetic region that had an intrusive structure, namely a positive polarity penetrating into a negative counterpart. The geometrical relationship between the sheared coronal arcade and the triggering region was consistent with the theoretical flare model based on the previous numerical study. We found that the formation of the trigger region was due to a continuous accumulation of the small-scale magnetic patches. A few hours before the flare occurrence, the series of emerged/advected patches reconnected with a preexisting fields. Finally, the abrupt flare eruption of the M6.6 event started around 17:30 UT. Our analysis suggests that, in a triggering process of a flare activity, all magnetic systems of multiple scales, not only the entire AR evolution but also the fine magnetic elements, are altogether involved. Subject headings: Sun: activity -Sun: flares -Sun: magnetic fields Recently, a systematic study of three-dimensional magnetohydrodynamic (MHD) simulations in terms of the flare-triggering mechanisms has been performed by Kusano et al. (2012). They modeled the preexisting coronal arcade overlying the PIL of an AR and a triggering field injected at the bottom boundary. By varying the shear angle of the coronal arcade and the azimuth angle of the injected flux, they systematically surveyed the conditions of the flare onset. As a result, it is found that there are two different types for the flare onset depending on the azimuth angle of the injected flux (Figure 1). One is the opposite-polarity (OP) case, where the injected bipole on the PIL has an opposite orientation to the overlying arcade (Panel a), and the other is the reversed-shear (RS) case, where the azimuth of the bipole is sheared in a reversed sense to the arcade (Panel b).

Redefining the Boundaries of Interplanetary Coronal Mass Ejections From Observations at the Ecliptic Plane

“…This protrusion is similar to the one described in Toriumi et al (2013), which produced strong flaring activity and in the end it involved filament eruption.…”

Magnetohydrodynamic Simulations for Studying Solar Flare Trigger Mechanism

“…The ribbons mark the footpoints of magnetic field lines that reconnect during the flare. A proxy for flare ribbons in the simulations is made by following the method introduced by Toriumi et al (2013) and applied also in Inoue et al (2014). We calculate the total displacement of the footpoint for each field line for a given time and consider field lines with a large footpoint displacement to be reconnected ones.…”

“…Reversed shear polarity refers to the small bipole structure which is directed nearly opposite to the shear component of the field. In order to examine the model of the solar flare trigger mechanism proposed by Kusano et al (2012), several observational analyses of flare events have been conducted by using Hinode (Kusano et al 2012;Bamba et al 2013;Toriumi et al 2013), SDO (Bamba et al 2014), SOHO/MDI (Park et al 2013), and New Solar Telescope (NST) data (Wang et al 2017). From their results, several flare events can be explained to occur as a result of the flare trigger mechanism proposed in Kusano et al (2012).…”

The physical mechanisms that initiate and drive solar eruptions

“…Eruptions driven by this process were modeled in the context of small-scale flux emergence in the vicinity of the flux rope, in the 2D electric-wire paradigm (Lin et al 2001), in 2.5D MHD simulations (Chen & Shibata 2000) and recently in 3D simulations (Kusano et al 2012;Toriumi et al 2013). It was also found to operate in 3D MHD models…”