Formation of Magnetic Flux Ropes during Confined Flaring Well Before the Onset of a Pair of Major Coronal Mass Ejections

TL;DR

This study identifies pre-eruption magnetic flux ropes in solar active region 11429, formed during confined flares, which later developed into two major coronal mass ejections, using multi-wavelength observations and magnetic field modeling.

Contribution

It reveals the formation of magnetic flux ropes during confined flares prior to major CMEs, providing insight into pre-eruption magnetic structures.

Findings

Detected two weakly-twisted pre-eruption flux ropes.

Flux ropes formed during confined flares before CMEs.

Pre-eruption flux ropes can seed major CMEs.

Abstract

NOAA Active Region (AR) 11429 was the source of twin super-fast Coronal Mass Ejections (CMEs). The CMEs took place within a hour from each other, with the onset of the first taking place in the beginning of March 7, 2012. This AR fulfills all the requirements for a "super active region"; namely, Hale's law incompatibility and a $\delta$-spot magnetic configuration. One of the biggest storms of Solar Cycle 24 to date ($D_{st}=-143$ nT) was associated with one of these events. Magnetic Flux Ropes (MFRs) are twisted magnetic structures in the corona, best seen in $\sim$10 MK hot plasma emission and are often considered the core of erupting structures. However, their "dormant" existence in the solar atmosphere (i.e. prior to eruptions), is an open question. Aided by multi-wavelength observations (SDO/HMI/AIA and STEREO EUVI B) and a Non-Linear Force-Free (NLFFF) model for the coronal magnetic field, our work uncovers two separate, weakly-twisted magnetic flux systems which suggest the existence of pre-eruption MFRs that eventually became the seeds of the two CMEs. The MFRs could have been formed during confined (i.e. not leading to major CMEs) flaring and sub-flaring events which took place the day before the two CMEs in the host AR 11429.