Unusual enhancement of ~ 30 MeV proton flux in an ICME sheath region

Mitsuo Oka, Takahiro Obara, Nariaki V. Nitta, Seiji Yashiro, Daikou Shiota, Kiyoshi Ichimoto

Research output: Contribution to journalArticlepeer-review

3 Citations (Scopus)


In gradual Solar Energetic Particle (SEP) events, shock waves driven by coronal mass ejections (CMEs) play a major role in accelerating particles, and the energetic particle flux enhances substantially when the shock front passes by the observer. Such enhancements are historically referred to as Energetic Storm Particle (ESP) events, but it remains unclear why ESP time profiles vary significantly from event to event. In some cases, energetic protons are not even clearly associated with shocks. Here, we report an unusual, short-duration proton event detected on 5 June 2011 in the compressed sheath region bounded by an interplanetary shock and the leading edge of the interplanetary CME (or ICME) that was driving the shock. While < 10 MeV protons were detected already at the shock front, the higher-energy (> 30 MeV) protons were detected about four hours after the shock arrival, apparently correlated with a turbulent magnetic cavity embedded in the ICME sheath region.[Figure not available: see fulltext.]

Original languageEnglish
Article number31
Journalearth, planets and space
Issue number1
Publication statusPublished - 2021 Dec


  • Coronal mass ejections
  • Interplanetary shocks
  • Particle acceleration
  • Solar energetic particles
  • Turbulence

ASJC Scopus subject areas

  • Geology
  • Space and Planetary Science


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