EGU21-421, updated on 03 Mar 2021
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

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

Mitsuo Oka1, Takahiro Obara2, Nariaki Nitta3, Seiji Yashiro4, Daikou Shiota5, and Kiyoshi Ichimoto6
Mitsuo Oka et al.
  • 1UC Berkeley, USA (
  • 2Tohoku University, Japan
  • 3Lockheed Martin Solar and Astrophysics Laboratory, USA
  • 4The Catholic University of America, USA
  • 5National Institute of Information and Communications Technology, Japan
  • 6Kyoto University, Japan

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.

How to cite: Oka, M., Obara, T., Nitta, N., Yashiro, S., Shiota, D., and Ichimoto, K.: Unusual enhancement of ~30 MeV proton flux in an ICME sheath region, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-421,, 2021.