An Observationally-Constrained Model of a Flux Rope that Formed in the Solar Corona

TL;DR

This study models a solar coronal flux rope prior to eruption, using observational data to analyze its magnetic structure and stability, providing insights into CME initiation mechanisms.

Contribution

It presents a detailed nonlinear force-free field extrapolation of a flux rope before eruption, linking magnetic stability criteria to CME onset.

Findings

Flux rope reached 150 Mm height before eruption

Estimated twist between 1.35 and 1.88 turns

Torus instability likely triggered the eruption

Abstract

Coronal mass ejections (CMEs) are large-scale eruptions of plasma from the coronae of stars. Understanding the plasma processes involved in CME initiation has applications to space weather forecasting and laboratory plasma experiments. James et al. (Sol. Phys. 292, 71, 2017) used EUV observations to conclude that a magnetic flux rope formed in the solar corona above NOAA Active Region 11504 before it erupted on 14 June 2012 (SOL2012-06-14). In this work, we use data from the Solar Dynamics Observatory to model the coronal magnetic field of the active region one hour prior to eruption using a nonlinear force-free field extrapolation, and find a flux rope reaching a maximum height of 150 Mm above the photosphere. Estimations of the average twist of the strongly asymmetric extrapolated flux rope are between 1.35 and 1.88 turns, depending on the choice of axis, although the erupting structure was not observed to kink. The decay index near the apex of the axis of the extrapolated flux rope is comparable to typical critical values required for the onset of the torus instability, so we suggest that the torus instability drove the eruption.