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

• Published in: Earth, planets, and space planets, and space, 2021-01, Vol.73 (1), p.31-31, Article 31
• Main Authors: Oka, Mitsuo, Obara, Takahiro, Nitta, Nariaki V., Yashiro, Seiji, Shiota, Daikou, Ichimoto, Kiyoshi
• Format: Article
• Language: English
• Subjects: 3. Space science; Coronal mass ejection; Coronal mass ejections; Earth and Environmental Science; Earth Sciences; Energetic particles; Express Letter; Geology; Geophysics/Geodesy; Interplanetary shocks; Natural history; Particle acceleration; Proton flux; Protons; Sheaths; Shock waves; Solar energetic particles; Solar-Terrestrial Environment Prediction: Toward the Synergy of Science and Forecasting Operation of Space Weather and Space Climate; Turbulence
• ISSN: 1343-8832; 1880-5981; 1880-5981
• DOI: 10.1186/s40623-021-01362-y

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  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.