Investigating the importance of seed particle populations in driving solar energetic particle intensity variations near Earth

Near-Earth spacecraft measurements of large Solar Energetic Particle (SEP) events during solar cycle 23 provided hints about the importance of the suprathermal seed population in determining the SEP properties (e.g., peak intensities, elemental composition) observed at 1 AU. However, despite significant advances in our understanding of SEP events, no single physical quantity associated with SEPs (e.g., CME speed) has yet exhibited a strong enough relationship with the SEP properties, leading to major difficulties in our ability to reliably predict the occurrence of extreme and potentially hazardous SEP events. This occurs primarily because by the time we observe SEP events at 1 AU, the effects of different physical processes of propagation and acceleration have already smeared the particle properties, which makes it virtually impossible to differentiate between the potentially distinct manifestations. The main objective of this proposal is to investigate the relative importance of the suprathermal seed population in driving the variations in peak intensities and fluences during a statistically significant sample of SEP events (>40) observed at 1 AU. To achieve this objective, we will analyze and model a number of SEP events from solar cycles 23 and 24 using multi-point solar wind, interplanetary magnetic field, and energetic particle observations from NASAs ACE, Wind, SoHO, and STEREO missions with a modified version of a state-of-art modeling code, the Energetic Particle Radiation Environment Module (EPREM), which was developed as a part of the Earth-Moon-Mars Radiation Environment Module (EMMREM) Project, currently adapted by NASAs Community Coordinated Modeling Center (CCMC).