Discriminate Between Homogenization Mechanisms in the Merged Ejecta

Determine whether the progressive weakening of thermodynamic contrasts between the two CME components results primarily from independent evolution toward near-isothermal states, plasma mixing within the merged magnetic-cloud-like ejecta, or a combination of both mechanisms.

Background

The proton polytropic analysis shows that the two thermodynamic regimes identified clearly near 0.37 au become increasingly similar at STEREO-A and Wind, approaching thermodynamic homogenization by 1 au.

The paper proposes two possible explanations: the two ejecta components may independently evolve toward near-isothermal states, or turbulent transport and kinetic instabilities may mix plasma from the two CME components within the merged structure. The available observations cannot distinguish between these alternatives.

References

The present observations, however, do not distinguish between these scenarios, and both mechanisms may contribute to the observed evolution.

— Evidence for CME--CME Interaction in a Magnetic-Cloud-Like Ejecta: Insights from Multipoint Observations and Polytropic Analysis  (2609.11554 - Sheoran et al., 10 Sep 2026) in Section 4.1, “Dual Polytropic index in ICME substructures”