Supergranular-scale magnetic flux emergence beneath an unstable filament

Abstract

Aims. Here we report evidence of a large solar filament eruption on 2013, September 29. This smooth eruption, which passed without any previous flare, formed after a two-ribbon flare and a coronal mass ejection towards Earth. The coronal mass ejection generated a moderate geomagnetic storm on 2013, October 2 with very serious localized effects. The whole event passed unnoticed to flarewarning systems. Methods. We have conducted multi-wavelength analyses of the Solar Dynamics Observatory through Atmospheric Imaging Assembly (AIA) and Helioseismic and Magnetic Imager (HMI) data. The AIA data on 304, 193, 211, and 94 Å sample the transition region and the corona, respectively, while HMI provides photospheric magnetograms, continuum, and linear polarization data, in addition to the fully inverted data provided by HMI.Results. This flux emergence happened very close to a filament barb that was very active in mass motion, as seen in 304 Å images. The observed flux emergence exhibited hectogauss values. The flux emergence extent appeared just beneath the filament, and the filament rose during the following hours. The emergence acquired a size of 33 in ∼12 h, about ∼0.16 km s −1 . The rate of signed magnetic flux is around 2 × 10 17 Mx min −1 for each polarity. We have also studied the eruption speed, size, and dynamics. The mean velocity of the rising filament during the ∼40 min previous to the flare is 115 ± 5 km s −1 , and the subsequent acceleration in this period is 0.049 ± 0.001 km s −2 . Conclusions. We have observed a supergranular-sized emergence close to a large filament in the boundary of the active region NOAA11850. Filament dynamics and magnetogram results suggest that the magnetic flux emergence takes place in the photospheric level below the filament. Reconnection occurs underneath the filament between the dipped lines that support the filament and the supergranular emergence. The very smooth ascent is probably caused by this emergence and torus instability may play a fundamental role, which is helped by the emergence.

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

“…Related to this, the spatial size and duration of the heating caused by internal reconnection within the trigger field represented by precursor brightenings is different among the events. In addition, empirically from this and other studies (Bamba et al 2013(Bamba et al , 2014Palacios et al 2015;Bamba et al 2017a,b;Wang et al 2017;Woods et al 2017), the duration varies from several hours to a few seconds and the spatial size were from a few to dozens of arcseconds.…”

“…Another interesting topic for discussion is the result that the OP type events were rare compared to the RS types, at least in this study. Some other studies found events which were suggested to be triggered by the OP type small magnetic structure (Palacios et al 2015;Wang et al 2017;Woods et al 2017). However, so far we found only two OP type flare events (already shown by Bamba et al (2013) by the same method of this study) whereas six events were classified as the RS type in this study.…”

Observational Analysis on the Early Evolution of a CME Flux Rope: Preflare Reconnection and Flux Rope’s Footpoint Drift

“…For many hot channel eruption events, their exact origin and initiation process still remain heated debated yet. Some observation supported that before the hot channel eruption, a corresponding MFR may already exist (e.g., Liu et al 2016;Wang et al 2016;) and slow photospheric flows might be important for its gradual formation (e.g., Yan et al 2018;Hou et al 2018;Vasantharaju et al 2019); while others argued that they can also be newly built up via rapid coronal reconnection during the eruption (Cheng et al 2011;Song et al 2014;Palacios et al 2015). For their loss-of-equilibrium, some researchers found that the loss-of-equilibrium of hot channel is initially facilitated by the breakout type (e.g., Chen et al 2016;Mitra et al 2018) or tether-cutting type (e.g., Chen et al 2014;Joshi et al 2015;Dudík et al 2016;Chen et al 2018) pre-flare reconnection, but others believed the loss-ofequilibrium of hot channel may be directly triggered the ideal MHD instabilities (e.g., Liu et al 2007;Bi et al 2015;Vemareddy et al 2017).…”

“…Thereinto, the latter two, jointly termed as the main phase, correspond to the impulsive acceleration of the erupting CME flux-rope, while the less-studied precursor phase includes key information on the eruptive structure and its trigger process. In the past, the limited observations showed that precursor activities of solar eruptions can come in various forms, in which preceding flux emergence (e.g., Palacios et al 2015;Yan et al 2017;Yang, & Chen 2019) or cancellation (e.g., Green et al 2011;Yang et al 2016;Chen et al 2018) in magnetograms, pre-eruption brightenings in H α /EUV images (e.g., Bi et al 2012;Dudík et al 2016;Wang et al 2017;Awasthi et al 2018;Chen et al 2018), as well as non-thermal processes in microwave or hard X-ray wavelength (Joshi et al 2011;Altyntsev et al 2012;Chen et al 2016) are most common ones. In recent years, in the precursor phase of many CME/flare eruptive events, a type of new progenitors of CME flux-ropes, namely hot channels (HCs, Cheng et al 2011;Zhang et al 2012;Cheng et al 2013), have been detected in the AIA high-temperature passbands (e.g., 131 and 94 Å).…”

Understanding the Role of Mass-Unloading in a Filament Eruption

“…A more detailed description on the physics of flux emergence may be found in Cheung and Isobe (2014). The flux emergence associated with filament eruptions can either be located directly beneath the flux rope, as described by Palacios et al (2015), or to the side. Emergence beneath the flux rope can trigger the eruption through tether-cutting, as described by Moore et al (2001).…”