Simulation of the 2010 September 9 Solar Energetic Particle Event by Using a Data-constrained Transport Model

Solar energetic particles (SEPs) can cause damage to spacecraft systems and affect human activities in space. On 2010 September 9, a gradual SEP event was observed by spacecraft STEREO-A, Solar and Heliospheric Observatory (SOHO), and STEREO-B at widely separated longitudes. For investigating the differences in the observed time–intensity profiles among the three spacecraft, we take a physics-based model to simulate the energetic particles produced by a coronal mass ejection (CME) shock propagating in the interplanetary medium. Constrained by the observational data of spacecraft, we describe a fast CME/shock transport in a steady-state solar wind background. The distribution of SEPs at the CME-driven shock is defined by a form consistent with diffusive shock acceleration theory. By solving the focused transport equation, the temporal evolution of SEP intensity can be obtained at different locations. We find that the simulated results successfully reproduce the important observational features of the SEP event. The energetic particles remaining from prior shock acceleration constituted one of the significant sources of SEPs observed by STEREO-B and SOHO during the decay phase of the event. In contrast, STEREO-A maintained a direct magnetic connection with the shock front throughout the shock propagation, resulting in a slower decay of the SEP intensity.