Solar Active Regions (ARs) are produced by the emergence of strong magnetic fields generated in the solar interior. ARs can be further classified into (a) simple and (b) complex. Simple ARs appear on the Sun as one magnetic bipole (i.e., composed of one positive and one negative magnetic polarity/sunspots) and they do not produce significant activity. Complex ARs are composed of multiple polarities and can be the source of intense explosive activity on the Sun, producing solar flares and CMEs. In this presentation, we focus on such complex and developing ARs composed of multiple magnetic bipoles that emerge in close proximity to each other. Due to the compact clustering of the different emerging bipoles within such complex multipolar ARs, collision and shearing between opposite non-conjugated polarities produce “collisional polarity inversion lines” (cPILs) and drive rapid cancellation of magnetic fields at the surface of the Sun. The strength and the duration of the collision, shearing, and cancellation are defined by the orientation and the natural separation of the conjugated polarities during the emergence phase of each bipole in the host AR. This scenario is called “Collisional Shearing”. Chintzoglou et al (2019) demonstrated that collisional shearing occurred in two well-observed emerging and evolving flare- and CME-productive ARs (NOAA AR11158 and AR12017) by measuring significant amounts of magnetic flux canceling at the cPIL. Our proposed scenario supports the recurrent formation and energization of magnetic flux ropes (i.e., twisted magnetic field structures) before their eruption as CMEs.

New results from advanced 3D radiative MHD simulations of Collisional Shearing will be pre- sented together with observations. We will discuss the relevance of these results in explaining the cause of recurrent explosive activity on the Sun.