Three-Dimensional Magnetic Restructuring in Two Homologous Solar Flares in the Seismically Active Noaa Ar 11283

Abstract

We carry out a comprehensive investigation comparing the three-dimensional magnetic field restructuring, flare energy release, and the helioseismic response, of two homologous flares, the 2011 September 6 X2.1 (FL1) and September 7 X1.8 (FL2) flares in NOAA AR 11283. In our analysis, (1) a twisted flux rope (FR) collapses onto the surface at a speed of 1.5 km s −1 after a partial eruption in FL1. The FR then gradually grows to reach a higher altitude and collapses again at 3 km s −1 after a fuller eruption in FL2. Also, FL2 shows a larger decrease of the flux-weighted centroid separation of opposite magnetic polarities and a greater change of the horizontal field on the surface. These imply a more violent coronal implosion with corresponding more intense surface signatures in FL2. (2) The FR is inclined northward, and together with the ambient fields, it undergoes a southward turning after both events. This agrees with the asymmetric decay of the penumbra observed in the peripheral regions.(3) The amounts of free magnetic energy and nonthermal electron energy released during FL1 are comparable to those of FL2 within the uncertainties of the measurements. (4) No sunquake was detected in FL1; in contrast, FL2 produced two seismic emission sources S1 and S2 both lying in the penumbral regions. Interestingly, S1 and S2 are connected by magnetic loops, and the stronger source S2 has weaker vertical magnetic field. We discuss these results in relation to the implosion process in the low corona and the sunquake generation.

Gradual Magnetic Evolution of Sunspot Structure and Filament–corona Dynamics Associated With the X1.8 Flare in Ar11283

“…Both X-class flares occurred in similar areas in this AR (Liu et al 2014). The yellow line in panel (c) delineates an "L"-shaped PIL.…”

“…As mentioned, it released two X-class flares on September 6 and 7, respectively. The eruption processes of both events have been well studied by many authors (Wang et al 2012;Feng et al 2013;Jiang & Feng 2013;Zharkov et al 2013;Liu et al 2014;Ruan et al 2014;Shen et al 2014). Thus, the details of the overall evolution of this AR will not be repeated here.…”

“…Many previous studies have focused on flare-induced changes of the photospheric magnetic field and sunspot structures (e.g., Severny 1964;Wang et al 1994;Spirock et al 2002;Yurchyshyn et al 2004;Wang & Liu 2010;Wang et al 2012;Liu et al 2014). Over the past five decades, with growing observational capabilities it has been established that the sunspot structure and corresponding photospheric magnetic field may change suddenly and irreversibly after flares.…”

“…In a recent study, Liu et al (2014) presented a comprehensive comparison of two major events released from the same NOAA active region (AR 11283). Both events are characterized by X-class flares (an X2.1 flare on 2011 September 6 and an X1.8 flare on September 7) with fast filament eruptions and coronal mass ejections (CMEs).…”

A unified view of coronal loop contraction and oscillation in flares

“…Benz 2008;Shibata & Magara 2011;Su et al 2013) that the energy required to power flares is released from magnetic fields in the corona by rapid magnetic reconfiguration, which may be enabled by magnetic reconnection. The direct coronal magnetic field measurements required to conclusively prove this are not presently possible, however, less direct estimates of changes to the coronal free magnetic energy using magnetic extrapolations generally support this view (Schrijver et al 2008;Jing et al 2010;Sun et al 2012;Malanushenko et al 2014;Liu et al 2014). The hypothesised rapid reconfiguration of the coronal magnetic field implies quick changes to the j × B Lorentz force acting on the coronal plasma, and these changes should have a variety of consequences, including coronal collapse and changes to photospheric magnetic fields, both of which are observed (references in Sect.…”