On the Constraints and Observational Manifestations of Failed Solar Eruptions in Toroidal Magnetic Cage

TL;DR

This study uses 3D MHD simulations and particle diagnostics to explore how strong toroidal magnetic fields influence the confinement, rotation, and observational signatures of failed solar eruptions within magnetic cages.

Contribution

It reveals the critical role of toroidal fields in eruption confinement, flux rope rotation, and flare morphology, advancing understanding of failed solar eruptions.

Findings

Toroidal fields generate return currents that suppress flux rope ascent.

Reconnection leads to flux rope rotation and break-up.

Synthetic emissions show distinct thermal and nonthermal signatures.

Abstract

Observations show that many solar eruptions remain confined within strong overlying magnetic fields, forming a so-called magnetic cage. While confinement by poloidal overlying fields has been widely investigated, the role of strong external toroidal fields remains unclear. Using three-dimensional magnetohydrodynamic simulations, we study confined eruptions in a toroidal magnetic cage, focusing on the interplay between the Lorentz force and magnetic reconnection, and their observational signatures. We further employ a guiding-center test-particle approach to synthesize hard X-ray emission for comparison between thermal and nonthermal responses. We find that overlying toroidal fields play a crucial role in confinement by generating strong return currents that produce a significant downward Lorentz force, suppressing flux rope ascent. At the same time, they induce large-angle rotation of the flux rope, leading to reconnection with overlying fields and eventual break-up. Synthetic EUV emission reveals multi-ribbon flares with highly sheared, globally cowboy-hat-like loop structures. Hard X-ray diagnostics show that thermal and nonthermal emissions are not co-spatial, with return currents acting as an efficient accelerator of energetic electrons. These results demonstrate that toroidal-field-induced forces govern both the confinement and rotation of erupting flux ropes, providing an explanation for failed eruptions even under torus-unstable conditions. These results suggest that the morphology and shearing angle of flare loops are the useful diagnostics for distinguishing confined from eruptive events.