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This paper presents a study of a 2021 October 9 coronal mass ejection (CME) with multipoint imaging and in situ observations. We also simulate this CME from the Sun to Earth with a passive tracer to tag 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 reveal that the propagation speed of the CME approaches about 1° hr−1, suggesting a slow CME. With 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 an ellipsoid to a concave shape owing 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 away from the Sun–Earth line. This means that the CME flank (or the ICME leg) likely arrives at both Solar Orbiter and the L1 point. From the CME's eruption to 1 au, its volume and mass increase by about two orders and one order of magnitude, respectively. Its kinetic energy is about 100 times larger than its magnetic energy at 1 au. These results have important implications for our understanding of CMEs' morphology, as well as their space weather impacts. [ABSTRACT FROM AUTHOR]

A global, three-dimensional (3D) numerical simulation model has been employed to study the 3D morphology and kinematics of the large shock driven by the 2017 September 10 coronal mass ejection (CME). Based on actual solar observations, which include the photospheric magnetic field and the CME's speed and source location, the simulation result is delicately tuned by matching with coronal polarized brightness observations and in situ solar-wind measurements at 1 au. The simulation reproduces well the shock's shape and position in coronagraphic images. The shock's physical parameters at 1 au are similar to those constrained from the observations, with the simulated transit time being nearly the same as the observed one. The simulation reveals that the shock around the backward direction keeps propagating away from the Sun, and despite its large extent, the shock cannot be seen as a spherical structure forming a 360° envelope around the Sun. Identified as a fast forward shock, the shock has a sharp velocity jump and a large density compression with a Mach number larger than one from the nose toward the lateral parts, consistent with a driven shock all across the front. Compared to the nose, the right flank of the shock has a weak compression ratio, but probably yields enhanced energetic particles for observers aligned with it. It follows that large CME-driven shocks have the potential to accelerate energetic particles over a wide longitudinal separation and are likely responsible for the production of these particles in the inner heliosphere. [ABSTRACT FROM AUTHOR]

Aimed to be ready for the transition from research to operation, we have developed a solar wind model by coupling a data-driven empirical coronal model with a magnetohydrodynamics heliospheric model. We performed a data-driven simulation of the solar wind for a two-year period during the declining and minimum phases of solar cycle 23. Comparisons with OMNI and Ulysses spacecraft data show that the model can reproduce the large-scale variations of the solar wind plasma parameters. The evolution of geocentric solar magnetospheric (GSM) Bx and Bz components are also reasonably duplicated by the model in terms of polarity and strength. Apparent signatures of the Russell–McPherron (R-M) effect are found from both observed data and simulated results, indicating that during the investigated interval the R-M effect is the dominant mechanism that controls the large-scale evolution of the north–south component of the interplanetary magnetic field in the GSM frame. The results demonstrate that the established model can provide valuable space weather information about the solar wind. [ABSTRACT FROM AUTHOR]