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

doi:10.1186/s40623-021-01362-y

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

Earth Planets Space. 2021;73(1):31. doi: 10.1186/s40623-021-01362-y. Epub 2021 Jan 29.

Authors

Mitsuo Oka¹, Takahiro Obara², Nariaki V Nitta³, Seiji Yashiro⁴, Daikou Shiota⁵, Kiyoshi Ichimoto⁶

Affiliations

¹ Space Sciences Laboratory, University of California Berkeley, Berkeley, CA USA.
² Planetary Plasma and Atmospheric Research Center, Tohoku University, Sendai, Japan.
³ Lockheed Martin Solar and Astrophysics Laboratory, Palo Alto, CA USA.
⁴ The Catholic University of America, Washington, DC 20064 USA.
⁵ National Institute of Information and Communications Technology, Koganei, Japan.
⁶ Graduate School of Science, Kyoto University, Kyoto, Japan.

Abstract

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.

Keywords: Coronal mass ejections; Interplanetary shocks; Particle acceleration; Solar energetic particles; Turbulence.