Numerical Simulations of Flare-productive Active Regions: delta-sunspots, Sheared Polarity Inversion Lines, Energy Storage, and Predictions

TL;DR

This study uses flux emergence simulations to explore how complex magnetic interactions in active regions lead to flare-productive delta-sunspots, revealing key magnetic parameters that predict flares and CMEs.

Contribution

The paper introduces detailed flux emergence simulations of various active region types, elucidating the formation of delta-sunspots and identifying magnetic parameters predictive of flares and CMEs.

Findings

Delta-spot formation results from magnetic field interactions.

High-gradient, highly-sheared PILs are created by advection, stretching, and compression.

Photospheric magnetic parameters accurately predict flare energy buildup.

Abstract

Solar active regions (ARs) that produce strong flares and coronal mass ejections (CMEs) are known to have a relatively high non-potentiality and are characterized by delta-sunspots and sheared magnetic structures. In this study, we conduct a series of flux emergence simulations from the convection zone to the corona and model four types of active regions that have been observationally suggested to cause strong flares, namely the Spot-Spot, Spot-Satellite, Quadrupole, and Inter-AR cases. As a result, we confirm that delta-spot formation is due to the complex geometry and interaction of emerging magnetic fields, with finding that the strong-field, high-gradient, highly-sheared polarity inversion line (PIL) is created by the combined effect of the advection, stretching, and compression of magnetic fields. We show that free magnetic energy builds up in the form of a current sheet above the PIL. It is also revealed that photospheric magnetic parameters that predict flare eruptions reflect the stored free energy with high accuracy, while CME-predicting parameters indicate the magnetic relationship between flaring zones and entire ARs.