第九届青年地学论坛

Solar active regions (ARs) are the main sources of flares and coronal mass ejections (CMEs). Under what circumstances an AR may produce confined or eruptive flares remains inconclusive. NOAA AR 12089 which emerged on 2014 June 10, produced two C-class eruptive flares within four hours after its emergence, while all subsequent flares were confined during its transit. To investigate why the AR produced eruptive flares so early, we compare the AR magnetic environment of the two eruptive flares to that of the largest confined flare (M1.1). We calculate the ratio between the mean characteristic twist parameter (α_FPIL) within the flaring polarity inversion line (FPIL) mask region and the total unsigned magnetic flux of the AR (ΦAR) for the three flares. The parameter considers the effects of both background magnetic field constraint and non-potentiality of the core region. We find that the αFPIL /ΦAR during the two eruptive flares is larger than the confined one. Furthermore, we compute the decay index along the polarity inversion line (PIL) before the onset of the three flares, revealing values of 1.77, 2.50, and 1.14, respectively. Finally, the evolution of the corona magnetic field was investigated by nonlinear force-free field extrapolation. The results indicate that before the eruptive flares, a flux rope was formed repeatedly through flux cancellation along the FPIL, which then ejected out and produced CMEs. Our research suggests that even a newly emerged, small AR can produce eruptive flares if it has sufficiently weak background field constraint and strong non-potentiality in the core region.