On Solar Energetic Particle Event Onsets Near-Earth

We previously reported a study of >10 MeV proton integral flux from near-Earth spacecraft investigating the arrival of Solar Energetic Particle Event, SEPE, protons near Earth in 1997-2005 [Christon et al., 2006]. SEPE protons are radiation hazards to space assets because they appear sporadically with variable, sometimes very high, intensity. Proton observations made between the sunward Lagrangian point (L1, about 225 Re sunward of Earth) and geosynchronous orbit in Earth's magnetosphere were collected for large, prompt proton flux enhancements. During some enhancements, the onset intensity-time profiles of >10-MeV and >30-MeV protons increase both at L1 and Earth within the 5- to 10-min averaging intervals used in the study. In this report we focus on these SEPE onsets to investigate different explanations for the above results. Using publicly available >10 MeV proton observations, we demonstrate a data-based scenario that may explain these SEPE onsets. Christon, S.P. et al. (2006), Spatial/Temporal Variations of SEP Ion Onsets From L1 To Near Earth's Magnetosphere, Eos Trans. AGU, 87(36), Jt. Assem. Suppl., Abstract.