Energy Dependence of SEP Electron and Proton Onset Times
Abstract
We study large solar energetic particle (SEP) events with > 10 MeV proton flux observed by GOES during solar cycle 24. Using multi-spacecraft observations from STEREO A, B and SOHO, we are able to determine accurately the solar particle release (SPR) time of SEP electrons and protons. We first compute connection angles (CA) between the solar events and magnetic foot-points connecting to each spacecraft. By choosing the smallest CA, we derive the electron and proton SPRs using electron fluxes from the SOHO Electron Proton and Helium Instrument (EPHIN), proton fluxes from the SOHO Energetic and Relativistic Nuclei and Electron instrument (ERNE), and from the High Energy Telescope (HET) on STEREO. We find that the proton SPRs inferred from high-energy channels (> 50 MeV) are similar to electron SPRs; the proton SPRs inferred from lower energy channel (5.12 - 16.9 MeV) can be delayed from the electron SPRs from tens of minutes to hours, especially for SEPs with large pre-event flux levels, suggesting that lower-energy protons might be trapped for a long time or suffer more scattering than higher-energy protons. We also find that for some large SEP events, the observed EPHIN electron and ERNE proton intensity profiles show a double-peak feature. The onset of the first peak corresponds well to the associated Type III and metric Type II onset.
- Publication:
-
Solar Heliospheric and INterplanetary Environment (SHINE 2015)
- Pub Date:
- July 2015
- Bibcode:
- 2015shin.confE..46X