Abstract
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 two hours before erupting as a CME.
Highlights
Coronal mass ejections (CMEs) are eruptions of billions of tonnes of plasma from the Sun, requiring large amounts of energy (≈ 1032 ergs)
CMEs that are able to escape the Sun and propagate through the heliosphere are sometimes referred to as interplanetary CMEs (ICMEs) when they are detected in situ
The Atmospheric Imaging Assembly (AIA) observations strongly support an interpretation that part of the magnetic field in NOAA Active Region 11504 transforms from a sheared arcade to a flux rope before the CME occurs
Summary
Coronal mass ejections (CMEs) are eruptions of billions of tonnes of plasma from the Sun, requiring large amounts of energy (≈ 1032 ergs). The only coronal energy source large enough to produce CMEs is magnetic energy, as kinetic, gravitational, and thermal energy fall short by orders of magnitude (Forbes, 2000). While it has been theorised that CMEs may be a method of releasing magnetic helicity in addition to magnetic energy from the corona (Rust, 1994), the physical processes behind the initiation and subsequent evolution of the eruptions remain unclear. When ICMEs are Earth-directed, they can drive phenomena that affect the Earth and the near-Earth environment, and these effects are known collectively as space weather. Early space weather forecasts are needed to allow preparation for the effects of Earth-directed ICMEs
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