A Comparative Study of the Eruptive and Non-eruptive Flares Produced by the Largest Active Region of Solar Cycle 24

Abstract

We investigate the morphological and magnetic characteristics of solar active region (AR) NOAA 12192. AR 12192 was the largest region of Solar Cycle 24; it underwent noticeable growth and produced 6 X-class flares, 22 M-class flares, and 53 C-class flares in the course of its disc passage. However, the most peculiar fact of this AR is that it was associated with only one CME in spite of producing several X-class flares. In this work, we carry out a comparative study between the eruptive and non-eruptive flares produced by AR 12192. We find that the magnitude of abrupt and permanent changes in the horizontal magnetic field and Lorentz force are significantly smaller in the case of the confined flares compared to the eruptive one. We present the areal evolution of AR 12192 during its disc passage. We find the flare-related morphological changes to be weaker during the confined flares, whereas the eruptive flare exhibits a rapid and permanent disappearance of penumbral area away from the magnetic neutral line after the flare. Furthermore, from the extrapolated nonlinear force-free magnetic field, we examine the overlying coronal magnetic environment over the eruptive and non-eruptive zones of the AR. We find that the critical decay index for the onset of torus instability was achieved at a lower height over the eruptive flaring region, than for the non-eruptive core area. These results suggest that the decay rate of the gradient of overlying magnetic field strength may play a decisive role to determine the CME productivity of the AR. In addition, the magnitude of changes in the flare-related magnetic characteristics are found to be well correlated with the nature of solar eruptions.

The source and engine of coronal mass ejections

“…The notable, intriguing counterexample of NOAA AR 12192 that hosted a large number of confined flares (e.g. [197]), possibly due to properties of the overlying magnetic field, eventually gave way to a single CME [198] before rotating to the far side. Substantial discussion has been already devoted to this exceptional target that warrants further investigation.…”

Lorentz Force Evolution Reveals the Energy Build-up Processes during Recurrent Eruptive Solar Flares

“…As the flare related major changes in horizontal magnetic field and Lorentz forces are expected to occur close to the polarity inversion line (PIL) (Wang 2006;Petrie & Sudol 2010;Petrie 2012;Sarkar & Srivastava 2018), we have selected subdomains (shown by the region enclosed by the green rectangular boxes in Figure 1) near the PIL on the flare productive part of each AR to carry out our analysis. As the recurrent flares studied in this paper occurred from the same part of the PIL, we are able to capture the evolution of the magnetic field over several days including the time of each flares within that same selected domain on the AR.…”

Failed prominence eruptions near 24 cycle maximum

“…The decay index in the flare-rich but CME-poor active region NOAA 12192 (2014 October) was lower than in CME-productive regions; n did not reach a value of 1.5 until a large height of more than 120 Mm, so the torus instability was unlikely (Sun et al 2015). The decisive role of the decay index heightdependence for the active-region CME-productivity was confirmed in many other flares (Vasantharaju et al 2018;Sarkar & Srivastava 2018).…”