Abstract
Abstract The X8.2 event of 2017 September 10 provides unique observations to study the genesis, magnetic morphology, and impulsive dynamics of a very fast coronal mass ejection (CME). Combining GOES-16/SUVI and SDO/AIA EUV imagery, we identify a hot (T ≈ 10–15 MK) bright rim around a quickly expanding cavity, embedded inside a much larger CME shell (T ≈ 1–2 MK). The CME shell develops from a dense set of large AR loops (≳0.5R s ) and seamlessly evolves into the CME front observed in LASCO C2. The strong lateral overexpansion of the CME shell acts as a piston initiating the fast EUV wave. The hot cavity rim is demonstrated to be a manifestation of the dominantly poloidal flux and frozen-in plasma added to the rising flux rope by magnetic reconnection in the current sheet beneath. The same structure is later observed as the core of the white-light CME, challenging the traditional interpretation of the CME three-part morphology. The large amount of added magnetic flux suggested by these observations explains the extreme accelerations of the radial and lateral expansion of the CME shell and cavity, all reaching values of 5–10 km s−2. The acceleration peaks occur simultaneously with the first RHESSI 100–300 keV hard X-ray burst of the associated flare, further underlining the importance of the reconnection process for the impulsive CME evolution. Finally, the much higher radial propagation speed of the flux rope in relation to the CME shell causes a distinct deformation of the white-light CME front and shock.
Highlights
Coronal mass ejections (CMEs) are large-scale structures of magnetized plasma that are expelled from the Sun with speeds ranging from ∼100 up to about 3500 km s−1
The CME associated with the X8.2 flare of 2017 September 10 provides us with unique observations on the genesis, magnetic morphology, and impulsive dynamical evolution of a very fast solar eruption
We clearly demonstrate that the hot bright rim observed around the quickly expanding EUV cavity is formed by the dominantly poloidal flux and the attached heated plasma that is added to the erupting flux rope by magnetic reconnection in the large-scale current sheet beneath, and that this structure extends into the coronagraph field of view (FOV) as the CME core
Summary
Coronal mass ejections (CMEs) are large-scale structures of magnetized plasma that are expelled from the Sun with speeds ranging from ∼100 up to about 3500 km s−1 (St. Cyr et al 1999; Gopalswamy et al 2009), driven by magnetic forces (e.g., reviews by Forbes et al 2006; Chen & Wu 2011; Green et al 2018). Cyr et al 1999; Gopalswamy et al 2009), driven by magnetic forces (e.g., reviews by Forbes et al 2006; Chen & Wu 2011; Green et al 2018) They are the most energetic events in our solar system, being associated with energy releases of up to ∼1032 erg (Vourlidas et al 2010; Emslie et al 2012). In particular owing to the multispacecraft in situ observations of the STEREO satellites, revealed the production of widespread solar energetic particles (SEPs), which seem to be able to fill
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