Understanding near-Earth energetic particle environment during large SEP events with the PATH code

The Particle Acceleration and Transport in the Heliosphere (PATH) one-dimensional numerical code has been developed to aid in understanding the influence of active events on/near the Sun on the near-Earth environment. The code incorporates both flare particles and particles accelerated at a CME-driven shock in their propagation throughout the inner heliosphere. As an example we present modeling results for the SEP event of December 13, 2006. The PATH code models propagating CME-driven oblique shock by perturbing a quiet-time solar wind at the inner boundary. The inner boundary conditions are extrapolated from ACE measurements at 1AU. Observed shock parameters at 1 AU and flare characteristics are used as input into the code. We assume a diffusive shock acceleration mechanism at the shock and model subsequent transport of particles escaping from the shock through the interplanetary medium to 1 AU. We focus on modeling spectra of protons, oxygen and iron ions and their time-intensity profiles. We numerically estimate Fe/O abundance ratio and discuss underlying physical scenario. Inter-comparison is made for the cases of oblique, quasi-parallel and quasi-perpendicular shocks. Our modeling results are compared with in situ measurements by ACE, STEREO, GOES and SAMPEX for this event.