[P-EM08] 宇宙天気・宇宙気候

[PEM08-P05] Unusual enhancement of ~30 MeV proton flux in an ICME sheath region

*小原 隆博¹、岡 光夫²、新田 就亮³、八代 誠二⁴、塩田 大幸⁵、一本 潔⁶ (1.東北大学　惑星プラズマ大気研究センター、2.UCバークレイ校、3.ロッキードマーティン太陽物理研究所、4.カトリック大学、5.情報通信研究機構、6.京都大学)

キーワード：太陽プロトン、衝撃波、加速

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.