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arXiv · 2604.12000

MMS Insights into CME Driven Sub-Alfv\'enic Solar Wind at 1 AU

Harsha Gurram·Li-Jen Chen·Matthew R. Argall·Subash Adhikari·Lynn B. Wilson·Jason R. Shuster·Victoria D. Wilder
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Abstract

We report the properties of electron distributions and turbulence during a Coronal Mass Ejection (CME) in April 2023 observed by Magnetospheric Multiscale (MMS). The CME exhibits a clear sheath and magnetic cloud (MC), and within the MC, the solar wind becomes sub-Alfv\'enic for two hours. We investigate plasma and turbulence properties of the sub-Alfv\'enic CME wind and compare them with those in the super-Alfv\'enic solar wind in the MC and CME sheath. Electrons within the sub-Alfv\'enic MC show significantly higher temperatures than those in the CME sheath and the super-Alfv\'enic MC, with their one-dimensional distributions revealing super-thermal tail and a depletion in electron populations between 15-50 eV. Within the CME sheath, isolated regions of electron heating are observed, where parallel energy flux is enhanced up to ~1 keV. Magnetic field fluctuations within the sub-Alfv\'enic MC interval exhibit negligible cross helicity and steeper-than-Kolmogorov scaling in the inertial range, with no clear spectral break. These fluctuations also show reduced intermittency at ion and sub-ion scales, emerging intermittency at electron scales, and weak magnetic compressibility. Together, these observations point to the presence of weak magnetohydrodynamic (MHD) turbulence within the sub-Alfv\'enic MC, resembling conditions commonly observed in planetary magnetospheres such as Jupiter's.

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Harsha Gurram, Li-Jen Chen, Matthew R. Argall, Subash Adhikari, Lynn B. Wilson, Jason R. Shuster, Victoria D. Wilder. 2026-04-13. MMS Insights into CME Driven Sub-Alfv\'enic Solar Wind at 1 AU. https://arxiv.org/abs/2604.12000

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