The Effects of Oscillations & Collisions of Emerging Bipolar Regions on the Triggering of Solar Flares

TL;DR

This study uses 3D magnetohydrodynamic simulations to explore how oscillations and collisions of small bipolar regions near the PIL influence the strength of solar flares, revealing that motion and interactions can significantly enhance flare intensity.

Contribution

It provides new insights into how small-scale bipolar region dynamics, including oscillations and collisions, affect solar flare triggering and strength, extending previous models.

Findings

Oscillations along the PIL increase flare strength.

Oscillations across the PIL decrease flare strength.

Colliding bipolar regions produce stronger flares.

Abstract

The ability to predict the occurrence of solar flares in advance is important to humankind due to the potential damage they can cause to Earth's environment and infrastructure. It has been shown in Kusano et al. (2012) that a small-scale bipolar region (BR), with its flux reversed relative to the potential component of the overlying field, appearing near the polarity inversion line (PIL) is sufficient to effectively trigger a solar flare. In this study we perform further 3D magnetohydrodynamic simulations to study the effect that the motion of these small-scale BRs has on the effectiveness of flare triggering. The effect of two small-scale BRs colliding is also simulated. The results indicate that the strength of the triggered flare is dependent on how much of the overlying field is disrupted by the BR. Simulations of linear oscillations of the BR showed that oscillations along the PIL increase the flare strength whilst oscillations across the PIL detract from the flare strength. The flare strength is affected more by larger amplitude oscillations but is relatively insensitive to the frequency of oscillations. In the most extreme case the peak kinetic energy of the flare increased more than threefold compared to a non-oscillating BR. Simulations of torsional oscillations of the BR showed a very small effect on the flare strength. Finally, simulations of colliding BRs showed the generation of much stronger flares as the flares triggered by each individual BR coalesce. These results show that significantly stronger flares can result from motion of the BR along the PIL of a sheared field or from the presence of multiple BRs in the same region.