Increase in high energy particle flux affected by an interplanetary shock wave

Abstract

An energetic proton event was observed at a geosynchronous orbit at nearly the same time as an interplanetary shock wave reached the Earth's magnetosphere, indicating that these two events interacted with each other during their passage to Earth. The variation of the energetic proton flux is not explained by the shock acceleration mechanism because there was no diffusive behavior upwind of the shock wave. These protons could have been ejected by a solar flare, because an energetic flare occurred at a well-connected position before the proton event, however, the delay time for the propagation of the energetic particles was too long if this flare was the origin of those particles. In the previous paper, we showed that the peculiar behavior of high-energy particles could be explained by the following scenario: the protons produced during a proton flare, which occurred after the CME, catch up with it and enter the turbulent region behind the shock wave, they are then scattered by the irregular magnetic field, that is, the Fermi acceleration, and are captured in the turbulent region behind the shock wave. In this paper, we obtain a scale of the irregularity of the turbulent magnetic field using Fourier transformation, compare it with a mean free path consistent with the one required from the observational data and the Larmor radius, and show that the proposed acceleration mechanism explains these events.