Flux Rope Formation Preceding Coronal Mass Ejection Onset

TL;DR

This study investigates the magnetic evolution of a sigmoidal active region leading up to a CME, providing evidence for a flux rope formation before eruption, driven by photospheric flux changes.

Contribution

It demonstrates the presence of a flux rope and a bald-patch separatrix surface in the corona prior to CME onset, linking magnetic topology changes to eruption.

Findings

Identification of a flux rope prior to CME

Detection of a bald-patch separatrix surface (BPSS)

Photospheric flux convergence and cancellation drive evolution

Abstract

We analyse the evolution of a sigmoidal (S shaped) active region toward eruption, which includes a coronal mass ejection (CME) but leaves part of the filament in place. The X-ray sigmoid is found to trace out three different magnetic topologies in succession: a highly sheared arcade of coronal loops in its long-lived phase, a bald-patch separatrix surface (BPSS) in the hours before the CME, and the first flare loops in its major transient intensity enhancement. The coronal evolution is driven by photospheric changes which involve the convergence and cancellation of flux elements under the sigmoid and filament. The data yield unambiguous evidence for the existence of a BPSS, and hence a flux rope, in the corona prior to the onset of the CME.