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

Alexander James   Submitted: 2018-02-27 09:22

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.

Authors: James, A. W., Valori, G., Green, L. M., Liu, Y., Cheung, M. C. M., Guo, Y., van Driel-Gesztelyi, L.
Projects: SDO-AIA,SDO-HMI

Publication Status: Accepted in ApJL
Last Modified: 2018-02-28 14:01
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On-disc Observations of Flux Rope Formation Prior to its Eruption  

Alexander James   Submitted: 2017-04-11 07:46

Coronal mass ejections (CMEs) are one of the primary manifestations of solar activity and can drive severe space weather effects. Therefore, it is vital to work towards being able to predict their occurrence. However, many aspects of CME formation and eruption remain unclear, including whether magnetic flux ropes are present before the onset of eruption and the key mechanisms that cause CMEs to occur. In this work, the pre-eruptive coronal configuration of an active region that produced an interplanetary CME with a clear magnetic flux rope structure at 1 AU is studied. A forward-S sigmoid appears in extreme-ultraviolet (EUV) data two hours before the onset of the eruption (SOL2012-06-14), which is interpreted as a signature of a right-handed flux rope that formed prior to the eruption. Flare ribbons and EUV dimmings are used to infer the locations of the flux rope footpoints. These locations, together with observations of the global magnetic flux distribution, indicate that an interaction between newly emerged magnetic flux and pre-existing sunspot field in the days prior to the eruption may have enabled the coronal flux rope to form via tether-cutting-like reconnection. Composition analysis suggests that the flux rope had a coronal plasma composition, supporting our interpretation that the flux rope formed via magnetic reconnection in the corona. Once formed, the flux rope remained stable for 2 hours before erupting as a CME.

Authors: A. W. James, L. M. Green, E. Palmerio, G. Valori, H. A. S. Reid, D. Baker, D. H. Brooks, L. van Driel-Gesztelyi, E. K. J. Kilpua
Projects: GOES X-rays,Hinode/EIS,Nançay Radioheliograph,SDO-AIA,SDO-HMI

Publication Status: Accepted
Last Modified: 2017-04-11 23:28
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An Observationally-Constrained Model of a Flux Rope that Formed in the Solar Corona
On-disc Observations of Flux Rope Formation Prior to its Eruption

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