AUTHOR=Liu Lijuan 

TITLE=The evolution of a spot–spot-type solar active region which produced a major solar eruption

JOURNAL=Frontiers in Astronomy and Space Sciences

VOLUME=Volume 10 - 2023

YEAR=2023

URL=https://www.frontiersin.org/journals/astronomy-and-space-sciences/articles/10.3389/fspas.2023.1135256

DOI=10.3389/fspas.2023.1135256

ISSN=2296-987X

ABSTRACT=Solar active regions (ARs) are the main sources of large solar flares and coronal mass ejections.
It is found that the ARs producing large eruptions usually show 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, which stresses the role of collision
and shearing induced by relative motions of different bipoles in their emergence. However, in
observations, if not considering the evolution stage of the ARs, about one third of the ARs that
produce large solar eruptions govern a spot-spot type configuration. In this work, we studied the
full evolution of an emerging AR, which owned a spot-spot type configuration when producing
a major eruption, to explore the possible evolution gap between “collisional shearing” process
in flux emergence and the formation of the spot-spot type, eruption-producing AR. We tracked
the AR from the very beginning of its emergence until it produced the first major eruption. It was
found that the AR was formed through three bipoles emerged sequentially. The bipoles were
arranged in parallel on the photosphere, shown as two clusters of sunspots with opposite-sign
polarities, so that the AR exhibited an overall large bipole configuration. In the fast emergence
phase of the AR, the shearing gradually occurred due to the proper motions of the polarities, but
no significant collision occurred due to the parallel arrangement of the bipoles. Nor did the large
eruption occur. After the fast emergence phase, one large positive polarity started to show signs
of decay. Its dispersion led to the collision to a negative polarity which belonged to another bipole.
A huge hot channel spanning the entire AR was formed through precursor flarings around the
collision region. The hot channel erupted later, accompanied by an M7.3-class flare. The results
suggest that in the spot-spot type AR, along with the shearing induced by the proper motions of
the polarities, a decay process may lead to the collision of the polarities, driving the subsequent
eruptions.