Gradual solar energetic particle (SEP) events, where particles are often accelerated to 10's of MeV energies, are associated with CME-driven shocks. As a CME-driven shock propagates, expands and weakens, particles are accelerated diffusively at the shock. A small number of these particles travel far enough upstream of the shock and escape into the interplanetary medium. These escaping energized particles then propagate along the interplanetary magnetic field (IMF), experiencing only weak scattering from fluctuations in the IMF. The detection of these energetic particles prior to the shock arrival often serves as a precursor for subsequent geomagnetic storms. Although the underlying acceleration mechanism, diffusive shock acceleration, is reasonably well understood theoretically, a comprehensive model that tracks particle acceleration and transport is necessary to interpret observations made by spacecraft such as ACE and WIND. In this paper, we discuss our dynamical model of particle acceleration and transport at a propagating CME-driven shock. The expanding shock is followed numerically using a shell model. The particle spectrum at the shock is decided by explicitly calculating the wave intensity due to streaming protons. The transport of the escaped particles is followed using a Monte-Carlo technique, which yields the predictions of the temporal intensity profile, particle spectra, etc. at 1 AU. We have applied this model to the April 21, 2002, event and find promising agreement between our model simulation and observations. We believe this approach may provide an important step towards understanding the influence of large SEP events in interplanetary and geospace environments.
|Title of host publication||Particle Acceleration in Astrophysical Plasmas|
|Subtitle of host publication||Geospace and Beyond|
|Publication status||Published - 2005|