Superexpansion of interplanetary coronal mass ejection observed by Solar Orbiter and Wind spacecraft within 0.14 au radial separation

Shirsh Lata Soni; Ankush Bhaskar; R Selva Kumaran; David Miles

doi:10.1093/mnras/stag350

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Superexpansion of interplanetary coronal mass ejection observed by Solar Orbiter and Wind spacecraft within 0.14 au radial separation

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Superexpansion of interplanetary coronal mass ejection observed by Solar Orbiter and Wind spacecraft within 0.14 au radial separation

Shirsh Lata Soni, Ankush Bhaskar, R Selva Kumaran and David Miles

Monthly notices of the Royal Astronomical Society, Vol.548(3), stag350

05/01/2026

DOI: 10.1093/mnras/stag350

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Abstract

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. $n \propto r^{-2}$), 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.

Interplanetary coronal mass ejections

interplanetary magnetic fields, solar winds, superexpansion

Details

Title: Subtitle: Superexpansion of interplanetary coronal mass ejection observed by Solar Orbiter and Wind spacecraft within 0.14 au radial separation
Creators: Shirsh Lata Soni - University of Iowa
Ankush Bhaskar - Vikram Sarabhai Space Centre
R Selva Kumaran - Vikram Sarabhai Space Centre
David Miles - University of Iowa
Resource Type: Journal article
Publication Details: Monthly notices of the Royal Astronomical Society, Vol.548(3), stag350
DOI: 10.1093/mnras/stag350
ISSN: 0035-8711
eISSN: 1365-2966
Publisher: Oxford University Press
Grant note: Department of Physics and Astronomy, UIowa
We acknowledge the NASA-SPDF open data policy (https://cd aweb.gsfc.nasa.gov/) to make data publicly open for use. We are thankful to the sources for the CACtus CME catalogue, generated and maintained by the SIDC at the Royal Observatory of Belgium. We are also thankful to Johan for making the GCS modeling codes available at https://github.com/johan12345/gc s_python (doi:10.5281/zenodo.5084818) and for his suggestions. SLS acknowledges the financial assistance provided by the Department of Physics and Astronomy, UIowa, through a Research Fellowship.
Language: English
Date published: 05/01/2026
Academic Unit: Physics and Astronomy
Record Identifier: 9985157614902771

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