Evolutionary stages and triggering process of a complex eruptive flare with circular and parallel ribbons

Abstract

We report multiwavelength study of a complex M-class solar eruptive flare that consists of three different sets of flare ribbons, viz. circular, parallel, and remote ribbons. Magnetic field modelling of source active region NOAA 12242 exhibits the presence of 3D null-point magnetic topology that encompasses an inner bipolar region. The event initiates with the faint signatures of the circular ribbon along with remote brightening right from the pre-flare phase that points toward the ongoing slow yet persistent null-point reconnection. We first detected flux cancellation and an associated brightening, which are likely signatures of tether-cutting reconnection that builds the flux rope near the polarity inversion line (PIL) of the inner bipolar region. In the next stage, with the onset of M8.7 flare, there is a substantial enhancement in the brightening of circular ribbon, which essentially suggests an increase in the rate of ongoing null-point reconnection. Finally, the eruption of underlying flux rope triggers ‘standard flare reconnection’ beneath it producing an abrupt rise in the intensity of the parallel ribbons as well as enhancing the rate of null-point reconnection by external forcing. We show that within the the fan dome, the region with magnetic decay index n > 1.5 borders the null-point QSL. Our analysis suggests that both the torus instability and the breakout model have played role toward the triggering mechanism for the eruptive flare. This event is a nice example of the dynamical evolution of a flux rope initially confined in a null-point topology that subsequently activates and erupts with the progression of the circular-cum-parallel ribbon flare.

Energy Partition in Four Confined Circular-Ribbon Flares

“…Contrary to two-ribbon flares, circular-ribbon flares (CRFs) are a special type of flares that consist of a short, compact inner ribbon and a bright, outer ribbon with a circular or elliptical shape (Masson et al, 2009;Joshi et al, 2015;Liu et al, 2015;Hernandez-Perez et al, 2017;Devi et al, 2020;Kashapova et al, 2020;Prasad et al, 2020;Joshi, Joshi, and Mitra, 2021). The three-dimensional (3D) magnetic configuration of CRFs is usually related to a fan-spine structure associated with a magnetic null point (Wang and Liu, 2012;Zhang et al, 2012;Sun et al, 2013;Hou et al, 2019;Lee et al, 2020;Liu et al, 2020;Yang et al, 2020;Zhang et al, 2021).…”

Homologous Compact Major Blowout-eruption Solar Flares and their Production of Broad CMEs

“…The interpretation of solar flares in the 3D regime is based upon several complex characteristics: coronal sigmoids (Sterling & Hudson 1997;Moore et al 2001;Aulanier et al 2010;Green et al 2011;Joshi et al 2017aJoshi et al , 2018Mitra et al 2018), systematic HXR footpoint motions along flare ribbons (Fletcher & Hudson 2002;Joshi et al 2009), and sheared flare loops (Asai et al 2003;Warren et al 2011). In addition to these complex magnetic features, some new aspects of the flare ribbons in the 3D domain have been identified, such as photospheric current ribbons (Janvier et al 2014), three flare ribbons (Wang et al 2014), circular flare ribbons (Masson et al 2009;Sun et al 2013;Devi et al 2020;Joshi et al 2021;, J-shaped ribbons (Chandra et al 2009;Schrijver et al 2011;Savcheva et al 2015;Joshi et al 2017b), etc. Since the nature of solar flares is intrinsically 3D, the energy release processes via magnetic reconnection are supposed to be 3D in nature.…”

Statistical analysis of circular-ribbon flares

“…Apart from the typical two-ribbon flares, there is another class of flares, i.e., circular-ribbon flares (CFs), whose ribbons are elliptical or circular (Masson et al 2009). It is generally believed that the three-dimensional (3D) magnetic configuration of CFs is composed of a null point and the associated dome-shaped fan-spine structure in the corona (e.g., Reid et al 2012;Wang & Liu 2012;Jiang et al 2013;Sun et al 2013;Vemareddy & Wiegelmann 2014;Joshi et al 2015Joshi et al , 2021Liu et al 2015;Zhang et al 2015Zhang et al , 2021. Sometimes, the outer spine is embedded in a thin quasi-separatrix layer (QSL; Demoulin et al 1996) where magnetic connectivity changes rapidly (Masson et al 2009;Yang et al 2015;Li et al 2018).…”

“…Interestingly, Zhang et al (2020) reported fast degradation of a circular ribbon at speeds of 30−70 km s −1 on 2014 August 24. Remote brightenings are frequently observed adjacent to the main flare site as a result of energy transport along the outer spine (Masson et al 2009(Masson et al , 2017Zhang et al 2015;Hernandez-Perez et al 2017;Li et al 2017;Devi et al 2020;Joshi et al 2021). Extended remote brightenings with a length of ∼400 ′′ is investigated by Liu et al (2020).…”