Magnetic Flux and Magnetic Nonpotentiality of Active Regions in Eruptive and Confined Solar Flares

Abstract

With the aim of understanding how the magnetic properties of active regions (ARs) control the eruptive character of solar flares, we analyze 719 flares of Geostationary Operational Environmental Satellite (GOES) class ≥C5.0 during 2010–2019. We carry out the first statistical study that investigates the flare-coronal mass ejection (CME) association rate as a function of the flare intensity and the AR characteristics that produce the flare, in terms of its total unsigned magnetic flux (Φ AR ). Our results show that the slope of the flare–CME association rate with flare intensity reveals a steep monotonic decrease with Φ AR . This means that flares of the same GOES class but originating from an AR of larger Φ AR , are much more likely to be confined. Based on an AR flux as high as 1.0 × 10 24 Mx for solar-type stars, we estimate that the CME association rate in X100-class “superflares” is no more than 50%. For a sample of 132 flares ≥M2.0 class, we measure three nonpotential parameters including the length of steep gradient polarity-inversion line ( L SGPIL ), the total photospheric free magnetic energy ( E free ), and the area with large shear angle ( A Ψ ). We find that confined flares tend to have larger values of L SGPIL , E free , and A Ψ compared to eruptive flares. Each nonpotential parameter shows a moderate positive correlation with Φ AR . Our results imply that Φ AR is a decisive quantity describing the eruptive character of a flare, as it provides a global parameter relating to the strength of the background field confinement.