Work

Assessing Accumulation and Erosion of Interplanetary Coronal Mass Ejections Using Lined-up Spacecraft

Year: 2026

Type: article

Abstract: Interplanetary coronal mass ejections (ICMEs), the large-scale solar transients carrying flux ropes (FRs), may evolve in different ways, including erosion and/or accumulation of magnetic field lines while being involved in magnetic reconnection with ambient solar wind and often with other nearby ICMEs and solar wind structures. In this Letter, for the first time utilizing a rare alignment of spacecraft, we analyse the multiscale radial evolution of two ICMEs—observed by spacecraft pairs with minimal angular separations of 2 . ° 2 and 1 . ° 1, and radial separations of 0.15 and 0.05 au, respectively—due to erosion and accumulation. We derive their magnetic helicity and cross helicity, residual and average magnetic energy, FR radial size, temporal extension of their helical structures, and the core’s characteristic scale size, and compare these parameters at the radial distances of the lined-up spacecraft to obtain their radial scaling. We find that if an expanding FR undergoes erosion at its outer layer during heliospheric propagation, its overall size expansion rate is lower than that of its core, where field line helicity is maximum. Conversely, during field line accumulation or merging, the expansion rate of FR overall size is higher than that of its core. Furthermore, erosion is indicated by a decreasing dominance of magnetic energy relative to total energy and a higher rate of average magnetic energy decay than ideally expected. These results demonstrate that coordinated multispacecraft observations can distinguish between erosion and accumulation processes in ICME FRs and provide new constraints on their dynamical evolution in the heliosphere.

Source: The Astrophysical Journal Letters

DOI: 10.3847/2041-8213/aeac5a