ABSTRACT Coronal mass ejections (CMEs) are large-scale expulsions of plasma and magnetic fields from the solar corona. As CMEs propagate through the heliosphere, their internal plasma and magnetic field structures undergo significant expansion and evolution, which influences their geoeffectiveness and interactions with planetary environments. This study investigates the radial evolution of a magnetic cloud (MC) structure observed near 1 au over a heliocentric distance of 0. 14 au, during the interplanetary CME event of 2021 November 4–5. The event was captured simultaneously by Solar Orbiter at 0. 84 au (sub-L1), and by Wind at 0. 98 au (L1). Using in situ plasma and magnetic field data, we estimate the interplanetary CME (ICME) expansion rates at both spacecraft and compute the dimensionless expansion parameter, confirming a superexpanding behaviour that exceeds typical observations in the past. Pressure diagnostics reveal that, although magnetic pressure within the MC decreases with distance, the thermal pressure shows an unusual sharp rise, deviating from the typical radial decay pattern. These results suggest possible ongoing plasma heating and momentum redistribution within the MC. The radial decay exponents derived for density (n) and pressure parameters deviate from the expected heliospheric scaling laws of MCs (e. g. n r^-2), suggesting the presence of non-uniform expansion processes, possible energy exchange, or local compressive effects within the magnetic cloud structure. Our results highlight the dynamic nature of MC evolution in the inner heliosphere and underscore the importance of sub-L1 observations in studying ICME evolution, thereby contributing to assessing and predicting ICME-driven space weather effects.
Soni et al. (Tue,) studied this question.