SOLARNET Conference: The Many Scales of the Magnetic Sun

It is often observed that the Sun produces repetitive coronal mass ejections (CMEs) with similar morphological features originating from the same source region. This kind of CMEs is known as homologous CMEs and their occurrence is majorly controlled by the storage of free magnetic energy in the active region corona. The stored energy is catastrophically released during flares, accompanied by successful eruption of plasma materials, to be observed as CMEs. Therefore, it is important to study the homologous flare-CME events in order to understand their association in terms of sustained energy build-up in the corona. In this study, we select three homologous flare-CME events of successively increasing flaring intensities (M2.0, M2.6, X1.0) originated in NOAA AR 12017 during 2014 March 28-29. We analyze the detailed evolution of the photospheric line-of-sight magnetogram from ≈1 day before the first event and encompassing all the three events. Our observations reveal significant phases of emergence and cancellation of magnetic flux in and around the flaring region, which strongly supports the idea of ‘tether-cutting’ model as a plausible triggering mechanism of the eruptions. We also analyze the build-up and release of free magnetic energy in the active region corona, which temporally correlates with a prolonged phase of magnetic flux emergence. The importance of this study lies in the investigation of the intrinsic coupling of magnetic fields and associated processes from the photosphere to corona that resulted into the repetitive build-up and eruption of magnetic flux ropes. Interestingly, the homologous flux rope eruptions led to broad CMEs (angular width ≈100° to 360°), in spite of their origin from compact eruption-source site. We investigate this apparent observational paradox in the framework of generalized ‘magnetic-arch blowout’ scenario, which satisfactorily explains the observed phenomena.