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Coronal mass ejections (CMEs) are large-scale eruptions of plasma from thecoronae of stars. Understanding the plasma processes involved in CME initiationhas applications to space weather forecasting and laboratory plasmaexperiments. James et al. (Sol. Phys. 292, 71, 2017) used EUV observations toconclude that a magnetic flux rope formed in the solar corona above NOAA ActiveRegion 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 magneticfield of the active region one hour prior to eruption using a nonlinearforce-free field extrapolation, and find a flux rope reaching a maximum heightof 150 Mm above the photosphere. Estimations of the average twist of thestrongly asymmetric extrapolated flux rope are between 1.35 and 1.88 turns,depending on the choice of axis, although the erupting structure was notobserved to kink. The decay index near the apex of the axis of the extrapolatedflux rope is comparable to typical critical values required for the onset ofthe torus instability, so we suggest that the torus instability drove theeruption.

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