The Source Locations of Major Flares and CMEs in Emerging Active Regions

Abstract

Abstract Major flares and coronal mass ejections (CMEs) tend to originate from compact polarity inversion lines (PILs) in solar active regions (ARs). Recently, a scenario named “collisional shearing” was proposed by Chintzoglou et al. to explain the phenomenon, which suggests that the collision between different emerging bipoles is able to form a compact PIL, driving the shearing and flux cancellation that are responsible for the subsequent large activities. In this work, by tracking the evolution of 19 emerging ARs from their birth until they produce the first major flares or CMEs, we investigated the source PILs of the activities, i.e., the active PILs, to explore the generality of “collisional shearing.” We find that none of the active PILs is the self PIL (sPIL) of a single bipole. We further find that 11 eruptions originate from the collisional PILs (cPILs) formed due to the collision between different bipoles, six from the conjoined systems of sPIL and cPIL, and two from the conjoined systems of sPIL and ePIL (external PIL between the AR and the nearby pre-existing polarities). Collision accompanied by shearing and flux cancellation is found to develop at all PILs prior to the eruptions, with 84% (16/19) cases having collisional length longer than 18 Mm. Moreover, we find that the magnitude of the flares is positively correlated with the collisional length of the active PILs, indicating that the more intense activities tend to originate from PILs with more severe collisions. The results suggest that “collisional shearing,” i.e., bipole–bipole interaction during the flux emergence, is a common process in driving the major activities in emerging ARs.