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Abstract

Solar active regions (ARs) that produce large solar eruptions usually own compact, highly-sheared polarity inversion lines (PILs). A scenario named as “collisional-shearing” is proposed to explain the formation of this type of PILs and the subsequent eruptions, stressing the role of collision and shearing induced by the relative motions of different bipoles in their emergence. However, if not considering the evolution stage of the ARs, about one third of the observed ARs that produce large solar eruptions govern a spot-spot type, i.e., an overall bipolar configuration. In this work, we studied the full evolution of an emerging, spot-spot type, eruption-producing AR, to explore the possible evolution gap between “collisional shearing” and the formation of the spot-spot type AR. It was found that the AR was formed through three bipoles emerged sequentially. The parallel arrangement of the bipoles made the AR exhibiting an overall bipolar configuration. In the fast emergence phase, the shearing gradually occurred due to the polarities’ imbalanced proper motions, but no significant collision occurred due to the bipoles’ parallel arrangement. Nor did the large eruption occur. After the fast emergence, one positive polarity started to decay, leading to collision to a non-conjugated negative polarity. A huge hot channel was formed through precursor flarings that initiated from the collision region. It erupted later, inducing an M7.3-class flare and a CME. The results suggest that even in the spot-spot type AR, the collision and shearing may also occur between non-conjugated polarities, playing a major role in producing the large eruptions.