Abstract
Abstract So far, most studies on the structure of coronal mass ejections (CMEs) are conducted through white-light coronagraphs, demonstrating that about one third of CMEs exhibit the typical three-part structure in the high corona (e.g., beyond 2 ), i.e., the bright front, the dark cavity, and the bright core. In this paper, we address the CME structure in the low corona (e.g., below 1.3 ) through extreme-ultraviolet (EUV) passbands and find that the three-part CMEs in the white-light images can possess a similar three-part appearance in the EUV images, i.e., a leading edge, a low-density zone, and a filament or hot channel. The analyses identify that the leading edge and the filament or hot channel in the EUV passbands evolve into the front and the core later within several solar radii in the white-light passbands, respectively. What is more, we find that the CMEs without an obvious cavity in the white-light images can also exhibit the clear three-part appearance in the EUV images, which means that the low-density zone in the EUV images (observed as the cavity in white-light images) can be compressed and/or transformed gradually by the expansion of the bright core and/or the reconnection of the magnetic field surrounding the core during the CME propagation outward. Our study suggests that more CMEs can possess the clear three-part structure in their early eruption stage. The nature of the low-density zone between the leading edge and the filament or hot channel is discussed.
Highlights
Coronal mass ejections (CMEs) are one of the most energetic explosions in the solar atmosphere, which can release large quantities of magnetized plasmas, magnetic fluxes, and energetic particles into the interplanetary space (Forbes et al 2006; Chen 2011; Webb & Howard 2012), and produce geomagnetic storms that may adversely impact human high-technology systems around the Earth (e.g., Gosling et al 1991; Webb et al 1994, 2000; Zhang et al 2003, 2007)
The EUV data sets are provided by three instruments, including the Atmospheric Imaging Assembly (AIA; Lemen et al 2012) on board the Solar Dynamics Observatory (SDO), the Extreme Ultraviolet Imager (EUVI; Howard et al 2008) on board the Solar Terrestrial Relations Observatory (STEREO), as well as the Solar Ultraviolet Imager (SUVI; Seaton & Darnel 2018) on board the GOES-16
The observations demonstrated that all the four coronal mass ejections (CMEs) can possess the three-part appearance in the EUV images, wherever they were associated with the eruption of a filament or a hot channel magnetic flux ropes (MFRs), and whether they had obvious cavity or not in the white-light images
Summary
Coronal mass ejections (CMEs) are one of the most energetic explosions in the solar atmosphere, which can release large quantities of magnetized plasmas, magnetic fluxes, and energetic particles into the interplanetary space (Forbes et al 2006; Chen 2011; Webb & Howard 2012), and produce geomagnetic storms that may adversely impact human high-technology systems around the Earth (e.g., Gosling et al 1991; Webb et al 1994, 2000; Zhang et al 2003, 2007). Howard et al (2017) conducted a survey based on 42 CMEs all with the three-part structure, which illustrated that ∼69% of the events are not associated with any eruptive filament They speculated that the CME core is produced by the geometric projection of a twisted MFR. Song et al (2017) clearly demonstrated that the hot channel MFR corresponds to the bright core through a filament-unrelated CME from both edge-on and face-on perspectives. The density structures in the white-light and the EUV passbands can be compared and correlated each other more straightforwardly for limb CMEs. We select four CMEs originating near the limb in this paper, including two (two) events with (without) the obvious cavity in the coronagraphs, which are associated with the eruption of a filament and a hot channel, respectively.
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