The peculiar behavior of high-energy particles affected by an interplanetary shock wave

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An energetic proton event was observed at a geosynchronous orbit nearly at the same time as an interplanetary shock wave reached the Earth's magnetosphere, which indicates that these two events interacted with each other during their passage to Earth. The behavior of the energetic protons is not explained by the shock acceleration mechanism since no enhancement of the proton flux occurred before the shock wave passage. Taking into account that a solar flare occurred at a well-connected position before the proton event, this flare is a candidate for the origin of the high-energy protons. However, the delay time for the propagation of the energetic particles was too long if those particles were ejected during that solar flare. In this paper, we show that the peculiar behavior of high-energy particles can be explained by the following scenario. The protons produced during a proton flare that occurred after the CME catch up with the CME, enter the turbulent region behind the shock wave, are scattered by an irregular magnetic field there, that is, the Fermi acceleration, and are captured in the turbulent region behind the shock wave. We estimate the increment of the momentum of the protons through the acceleration process and show that the acceleration mechanism considered explains these events. In our scenario, the proton arrival time may be delayed when a coronal mass ejection occurs before the energetic proton event.
国立極地研究所の論文