A heliospheric simulation-based approach to SEP source and transport modeling

Solar Energetic Particle (SEP) ion flux time profiles, continue to be a subject of interest because of the information they contain about sources and acceleration processes. STEREO and someday the LWS Sentinels missions have increased capabilities for resolving some of the outstanding questions raised by SEP profiles by means of regular multipoint SEP measurements over a wide energy and mass spectrum. Among these is the location and nature of the source(s) and the effects of source properties versus transport in determining the profiles. However, the interpretation of these data will require a more realistic description of the coronal and interplanetary source and transport geometries than previous approaches. In particular, the possibilities for tracing back minimally scattered SEP (>10 MeV) ions to their sources has greatly improved as a result of computational models of the coronal and interplanetary magnetic fields based on solar magnetograms. Here we use a heliospheric MHD simulation of the May 12, 1997 interplanetary coronal mass ejection to illustrate an approach to modeling the associated SEP event. Our approach assumes that the simulated shock is the moving source of the ions, and that a near-Earth spacecraft samples the fluxes on a sequence of field lines connected to that evolving source. It is found that the combination of a relatively simple shock source description and scatter-free propagation can approximate an observed SEP time profile. The approach emphasizes the importance of knowing the observer-connected shock source time history, which is difficult to include in a SEP event model without a realistic underlying model of the heliospheric event.