On the current understanding of large-scale flux ropes within solar coronal mass ejections

Abstract

Understanding the large-scale structure and evolution of coronal mass ejections (CMEs) is essential for accurately forecasting their space weather impacts at Earth and other planets. There are several open issues concerning the global shape, evolution and magnetic configuration of CME flux ropes as they travel through the heliosphere, notably their deformation, erosion, deflection, rotation and coherence. Extensive progress is currently made in both regimes of observations and modeling. All types of models, being numerical, empirical or analytical, have their advantages and disadvantages. While 3D-MHD models capture the physics of CMEs in detail, very fast models can map the full parameter space and can quickly interpret multipoint CME flux rope observations. With solar cycle 25 on the rise, the spacecraft fleet Parker Solar Probe, Solar Orbiter, BepiColombo, STEREO-A, and several probes at L1 now routinely provide us with multi-spacecraft lineup observations of the same CME event. This makes it possible to combine remote sensing and in situ observations to constrain CME models. However, entirely novel types of observations are driving the field forward now. In June and September 2022, Parker Solar Probe observed CMEs in situ at 0.07 AU, setting new records for the observations of CMEs closest to the Sun. In 2023, STEREO-A acted as the first sub-L1 monitor while passing the Sun-Earth line. In March 2022, Solar Orbiter was able to measure the magnetic flux rope of a CME in situ prior to Earth impact with a long lead time, for the first time in space science history. From early 2025, Solar Orbiter will provide out-of-ecliptic measurements of CMEs, which is a much needed perspective to constrain large-scale CME flux rope models. The PUNCH mission will provide polarized heliospheric images of CMEs, which leads to the exciting possibility to determine the handedness and possibly flux rope type from remote sensing observations. Distant retrograde mission concepts like MIIST and HENON could routinely sample CMEs at spatial separations of 1-10° and 0.01 to 0.1 AU in the 2030s, when also ESA Vigil is expected to start operations.