Global Morphology Distortion of the 2021 October 9 Coronal Mass Ejection from an Ellipsoid to a Concave Shape

This paper presents a study of 2021 October 9 coronal mass ejection (CME) with multipoint imaging and in situ observations, which include coronagraph and heliosphericimaging observations from the Solar TErrestrial RElations Observatory (STEREO)-A and SOlar and Heliospheric Observatory (SOHO), in connection with the plasma andmagnetic field measurements made at Solar Orbiter (SolO) and L1 point. We also simulate this CME from the Sun to Earth with a passive tracer to mark the CME’s motion. The coronagraphic images show that the CME is observed as a full halo by SOHO and as a partial halo by STEREO-A. The heliospheric images show that the propagation speed of the CME approaches to about 1 degree per hour, suggesting a slow CME. With the simulated results matching these observation results, the simulation discloses that as the CME ejects from the Sun out to interplanetary space, its global morphology is distorted from a quasi-spherical geometry into a concave-outward topology due to interactions with the bimodal solar wind. The cross section of the CME’s flux rope structure transforms from a circular shape into a flat one. As a result of the deflection, the propagation direction of the CME is far from the Sun-Earth line. This makes the plasma and magnetic field measurements at L1 point show a clear sheath region driven by the CME, while the SolO satellite measures the left flank of the CME. When the CME arrives at 1 AU, its volume and mass increase about 2 orders and about 1 order of magnitude, respectively. Its kinetic energy is about 100 times larger than its magnetic energy. These results have important implications for our understanding of CMEs’morphology as well as their space weather impacts.