Book Description

Coronal mass ejections (CMEs) are eruptions of billions of tonnes of plasma and associated magnetic fields from the solar atmosphere that can affect the near-Earth environment. In order to produce accurate long-term forecasts of space weather, we need to develop the ability to predict CMEs days before they occur. This requires a full understanding of the mechanisms involved in triggering and driving CMEs, which in turn involves discerning the pre-eruptive configuration of the coronal magnetic field. In this thesis, I use extreme-ultraviolet observations to infer that the preeruptive coronal configuration of a CME that occurred on 14 June 2012 was that of a magnetic flux rope. This flux rope formed in a hyperbolic flux tube (HFT) configuration via magnetic reconnection high up in the solar corona "†a scenario which has not previously been studied in great quantity or detail. It is proposed that the coronal reconnection that formed the flux rope was forced by the observed "orbiting" motion of newly-emerging magnetic flux in the photosphere. A numerical model of the coronal magnetic field on 14 June 2012 is produced via the nonlinear force-free field extrapolation of photospheric field measurements. The model shows exceptional agreement with the observational analysis, confirming the presence of the HFT flux rope. Furthermore, the model suggests that the eruption of the flux rope was driven by the torus instability. Four additional cases of pre-eruptive HFT flux ropes are identified, and similar photospheric "orbiting" motions are observed whilst the flux ropes formed. This suggests that these motions are systematically involved in triggering the formation of HFT flux ropes via magnetic reconnection in the corona.