@article{a2dd80fed69f430896b2dd4701494b72,
title = "Energetic ion enhancements in sheaths driven by interplanetary coronal mass ejections",
abstract = "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 Alfv{\'e}nic 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.",
keywords = "Coronal mass ejections, Interplanetary shocks, Particle acceleration, Solar wind",
author = "Emilia Kilpua and Rami Vainio and Christina Cohen and Nina Dresing and Simon Good and Julia Ruohotie and Domenico Trotta and Bale, {Stuart D.} and Eric Christian and Matt Hill and McComas, {David J.} and Ralph McNutt and Nathan Schwadron",
note = "Funding Information: This study has received funding through the European Union{\textquoteright}s Horizon 2020 research and innovation programme under grant agreement No 101004159 (SERPENTINE). EK acknowledges the ERC under the European Union{\textquoteright}s Horizon 2020 Research and Innovation Programme Project 724391 (SolMAG). The US authors were supported as a part of the PSP mission under contract NNN06AA01C. Work in the University of Turku and University of Helsinki was performed under the umbrella of Finnish Centre of Excellence in Research of Sustainable Space (Academy of Finland Grant no. 336809, 312390 and 336809). Parker Solar Probe was designed, built, and is now operated by the Johns Hopkins Applied Physics Laboratory as part of NASA{\textquoteright}s Living with a Star (LWS) program (contract NNN06AA01C). ND is grateful for support by the Academy of Finland (SHOCKSEE, grant No. 346902). Funding Information: This study has received funding through the European Union{\textquoteright}s Horizon 2020 research and innovation programme under grant agreement No 101004159 (SERPENTINE). EK acknowledges the ERC under the European Union{\textquoteright}s Horizon 2020 Research and Innovation Programme Project 724391 (SolMAG). The US authors were supported as a part of the PSP mission under contract NNN06AA01C. Work in the University of Turku and University of Helsinki was performed under the umbrella of Finnish Centre of Excellence in Research of Sustainable Space (Academy of Finland Grant no. 336809, 312390 and 336809). Parker Solar Probe was designed, built, and is now operated by the Johns Hopkins Applied Physics Laboratory as part of NASA{\textquoteright}s Living with a Star (LWS) program (contract NNN06AA01C). ND is grateful for support by the Academy of Finland (SHOCKSEE, grant No. 346902). Publisher Copyright: {\textcopyright} 2023, The Author(s).",
year = "2023",
month = aug,
doi = "10.1007/s10509-023-04201-6",
language = "English (US)",
volume = "368",
journal = "Astrophysics and Space Science",
issn = "0004-640X",
publisher = "Springer Netherlands",
number = "8",
}