The Origin of Major Solar Activity: Collisional Shearing between Nonconjugated Polarities of Multiple Bipoles Emerging within Active Regions

Abstract

Active Regions (ARs) that exhibit compact Polarity Inversion Lines (PILs) are known to be very flare-productive. However, the physical mechanisms behind this statistical inference have not been demonstrated conclusively. We show that such PILs can occur due to the collision between two emerging flux tubes nested within the same AR. In such multipolar ARs, the flux tubes may emerge simultaneously or sequentially, each initially producing a bipolar magnetic region (BMR) at the surface. During each flux tube's emergence phase, the magnetic polarities can migrate such that opposite polarities belonging to different BMRs collide, resulting in shearing and cancellation of magnetic flux. We name this process "collisional shearing" to emphasize that the shearing and flux cancellation develops due to the collision. Collisional shearing is a process different from the known concept of flux cancellation occurring between polarities of a single bipole, a process that has been commonly used in many numerical models. High spatial and temporal resolution observations from the Solar Dynamics Observatory for two emerging ARs, AR11158 and AR12017, show the continuous cancellation of up to -2 -40% of the unsigned magnetic flux of the smallest BMR, which occurs at the collisional PIL for as long as the collision persists. The flux cancellation is accompanied by a succession of solar flares and CMEs, products of magnetic reconnection along the collisional PIL. Our results suggest that the quantification of magnetic cancellation driven by collisional shearing needs to be taken into consideration in order to improve the prediction of solar energetic events and space weather.

Decoding the Pre-Eruptive Magnetic Field Configurations of Coronal Mass Ejections

“…Fang and Fan, 2015;Takasao et al, 2015;Toriumi and Takasao, 2017;Cheung et al, 2019;Syntelis et al, 2019c). We note that the nature of shear and its role for the formation and eruption of MFRs has been investigated also in observational studies, for cases of two colliding emerging bipoles (Chintzoglou et al, 2019). Here we focus on the formation of MFRs in quadrupolar ARs in flux-emergence simulations.…”

“…Flux emergence in multipolar ARs can eventually lead to the formation of MFRs (Chintzoglou et al, 2019). These authors reported observations of multiple bipoles, emerging either simultaneously or sequentially, in two emerging ARs.…”

“…The convergence of opposite magnetic polarities towards PILs that leads to flux cancellation is driven by the dispersion of decaying AR magnetic fields, through convection and emergence of AR bipoles into pre-existing magnetic field, and also by the collision of bipoles during the emergence of multipolar ARs. The process of flux cancellation is often observed leading up to the formation of filament channels, filaments and CMEs (Martin et al, 1985(Martin et al, , 2012Martin, 1998;Gaizauskas et al, 2001;Gaizauskas, 2002;Wang and Muglach, 2007;Mackay et al, 2008Mackay et al, , 2014Chintzoglou et al, 2019), suggesting that flux cancellation plays an important role in the construction of pre-eruptive magnetic-field configurations. Small-scale brightenings and jets have been observed in the corona in connection with cancellation sites (e.g., Wang and Muglach, 2013).…”

A physics-based method that can predict imminent large solar flares

“…However, the k-scheme cannot determine the lead time between when the condition is first satisfied and the onset of the flare. It is likely that small-scale magnetic structures favorable for magnetic reconnection (18,24), flux emergence and cancellation (25,26), and the collision of nonconjugated magnetic polarities (27) may determine the initiation of the triggerreconnection.…”

Trigger mechanisms of the major solar flares

“…Their results revealed that large ARs with widespread and/or strong shearing flows along PILs tend to produce major flares within 24 hr. Furthermore, Chintzoglou et al (2019) demonstrated that the opposite polarities belonging to different bipolar magnetic regions collide, resulting in shearing and cancellation of magnetic flux, and named this kind of motion "collisional shearing". Fig.…”