HR: 0830h
AN: SH11D-1148    [PDF]
TI: Modeling of an Energetic Particle Event Focused on Evolutionary Behavior in Low-Energy Range of a Proton Flux
AU: * Den, M
EM: den@crl.go.jp
AF: Communications Research Laboratory, 4-2-1, Nukuikita, Koganei, Tok 184-8795 Japan
AU: Yoshida, T
EM: yoshidat@mx.ibaraki.ac.jp
AF: Ibaraki University, 2-1-1, Bunkyo, Mito, Iba 310-8512 Japan
AU: Yamashita, K
EM: yamasita@edu.yamanashi.ac.jp
AF: University of Yamanashi, 4-4-37 Takeda, Kofu, Yam 400-8510 Japan
AB: Energetic particle acceleration events are thought to be associated with coronal mass ejection (CME)-driven shock waves. In our previous paper (Den, et al., 2001), we insisted that there are at least two types in gradual solar energetic particle (SEP) events. One is that the peak intensities of accelerated particles are below 10 MeV, they often coincide with the shock passage, and behavior of gradual enhancement of a particle flux preceding the shock passage indicates that a particle transport process is not apparent, namely an acceleration close to the sun is ineffective, and certainly no large X-ray flares are related with the source CMEs. The other is that the particles are accelerated to larger than 10 MeV, the large X-ray flares are correlated with the source CMEs very well and feature of a particle flux depends on the solar longitude where the source CME or associated large flare occurred. In this paper, using EPAM data on board the ACE spacecraft, we study time evolution of an energy spectrum of a proton flux in the range of 47 - 4750 keV for the energetic particle event occurred on 255 DOY in 1999, which is regarded as one of typical events of the former type. It is found that the energy spectrum in lower energy range, less than 0.5 MeV, enhanced faster, that is, the spectrum gets softer, which means that the acceleration mechanism is ineffective, and this behavior may give a key concerned with the seed population of the shock acceleration. In order to find energy dependence of a diffusive coefficient, we analyze the magnetic field data observed by MAG on board the ACE and obtain correlation function of the magnetic field. Our result shows that the diffusive coefficient is in proportion to a particle energy. We perform modeling this event including this consequence by numerical simulations using stochastic differential equation method. Our simulation results indicate that insufficiently accelerated particles may exist around 1 AU to explain the evolutionary behavior of the energy spectrum obtained by the observational data.
DE: 2114 Energetic particles, heliospheric (7514)
DE: 2118 Energetic particles, solar
DE: 2139 Interplanetary shocks
DE: 2164 Solar wind plasma
DE: 7513 Coronal mass ejections
SC: SPA - Solar and Heliospheric Physics [SH]
MN: 2003 Fall Meeting