Three-part structure of a solar coronal mass ejection observed in low coronal signatures of Solar Orbiter
Authors: Podladchikova Tatiana , Jain Shantanu , Veronig Astrid M. , Purkhart Stefan , Chikunova Galina , Dissauer Karin , Dumbović Mateja 
Published: October 2024

Context. Coronal mass ejections (CMEs) are large-scale eruptions of plasma and magnetic field from the Sun propagating through the heliosphere. Observations of the March 28, 2022, event provide unique images of a three-part solar CME in the low corona in active region 12975: a bright core or filament, a dark cavity, and a bright front edge.
Aims. We investigated the relationship between coronal dimming, filament eruption, and early CME propagation in this rarely seen case. We employed 3D filament and CME shock reconstructions along with estimations of early CME evolution inferred from the associated expansion of the coronal dimming.
Methods. We performed 3D reconstructions using data from Solar Orbiter, Solar TErrestrial RElations Observatory (STEREO-A), and Solar Dynamics Observatory (SDO) to analyse the path, height, and kinematics of the erupting filament. We developed the ATLAS-3D (Advanced Technique for single Line-of-sight Acquisition of Structures in 3D) method and validated it by comparing it to traditional approaches to reconstructing filament loops and the CME shock structure. ATLAS-3D uses Solar Orbiter data exclusively and integrates existing 3D filament reconstructions from the early stages of the event to establish spatial relationships between the filament and the CME frontal edge. Additionally, we employed the DIRECD method to estimate the characteristics of early CME propagation based on its coronal dimming evolution.
Results. The filament height increased from 28 to 616 Mm (0.04 to 0.89 Rsun) over 30 minutes, from 11:05 to 11:35 UT, with a peak velocity of 648 ± 51 km s−1 and a peak acceleration of 1624 ± 332 m s−2. At 11:45 UT, the filament deflected by about 12°, reaching a height of 841 Mm (1.21 Rsun). Simultaneously, the quasi-spherical CME shock expanded from 383 to 837 Mm (0.55 to 1.2 Rsun) between 11:25 and 11:35 UT. Over 10 minutes, the distance between the filament apex and the CME leading edge more than doubled, from approximately 93 to 212 Mm (0.13 to 0.3 Rsun),demonstrating significant growth and increasing separation between them. Key parameters estimated from DIRECD and the 3D filament reconstructions include the CME direction (inclined by 6° from radial expansion), a half-width of 21°, and a cone height of 1.12 Rsun, which was derived at the end of the dimming’s impulsive phase. The reconstructed 3D CME cone, which represents the inner part of the CME, closely matches the observed filament shape at 11:45 UT in terms of both height and angular width. Validation with white-light coronagraph data confirmed the accuracy of the 3D cone, particularly in terms of filament and CME characteristics, including projections to STEREO-A COR2 times.
Conclusions. The eruptive event on March 28, 2022, showed rapid filament development and its subsequent deflection from the primary propagation direction. This confirms that connections between dimming and CME expansion can be established by the end of the dimming’s impulsive phase, preceding the filament’s deflection at 11:45 UT, illustrating further self-similar CME evolution. Our approach links the expanding dimming with the early CME development, highlighting dimmings as indicators and the DIRECD method’s utility in correlating the 2D dimming with 3D CME structure. These findings provide valuable insights into early CME evolution and demonstrate the importance of using multi-viewpoint observations and novel reconstruction methods in space weather forecasting.