Energetic ion enhancements in sheaths driven by interplanetary coronal mass ejections

Emilia Kilpua, Rami Vainio, Christina Cohen, Nina Dresing, Simon Good, Julia Ruohotie, Domenico Trotta, Stuart D. Bale, Eric Christian, Matt Hill, David J. McComas, Ralph McNutt, Nathan Schwadron

Research output: Contribution to journalArticlepeer-review

1 Scopus citations


We analyze here an energetic proton enhancement in a sheath ahead of a slow interplanetry coronal mass ejection (ICME) detected by Parker Solar Probe on June 30, 2021 at the heliospheric distance of 0.76 AU. The shock was likely quasi-parallel and had a high Mach number. However, the proton fluxes were not enhanced at the shock but about an hour later. The fluxes stayed elevated with a sporadic behaviour throughout the sheath. We suggest that some mechanism internal to the sheath was responsible for the energization. The observations show enhanced levels of magnetic field fluctuations in the sheath and frequent presence of highly reduced magnetic helicity structures (σm) at various time scales, representing either small-scale flux ropes or Alfvénic fluctuations that could have contributed to the energization. The correlation between the energetic proton fluxes and normalized fluctuation amplitudes/occurrence of high σm structures was generally weak or negligible. The most striking feature of the sheath was a strong enhancement of density (up to 50 cm−3) that implies the importance of compressive acceleration in the sheath. A statistical analysis of ion enhancements of 73 sheaths detected by ACE at ∼ 1 AU reveals that this sheath was peculiar as in ICME-driven sheaths preceded by strong shocks the ion fluxes typically peak at the shock and strongly decline through the sheath.

Original languageEnglish (US)
Article number66
JournalAstrophysics and Space Science
Issue number8
StatePublished - Aug 2023

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Coronal mass ejections
  • Interplanetary shocks
  • Particle acceleration
  • Solar wind


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