Solar Energetic Particle Events with Protons above 500 MeV between 1995 and 2015 Measured with SOHO/EPHIN

摘要

The Sun is an effective particle accelerator producing solar energeticparticle (SEP) events during which particles up to several GeVs can beobserved. Those events observed at Earth with the neutron monitor network arecalled ground level enhancements (GLEs). Although these events with a highenergy component have been investigated for several decades, a clear relationbetween the spectral shape of the SEPs outside the Earth's magnetosphere andthe increase in neutron monitor count rate has yet to be established. Hence, ananalysis of these events is of interest for the space weather as well as thesolar event community. In this work, SEP events with protons accelerated toabove 500 MeV have been identified using data from the Electron Proton HeliumInstrument (EPHIN) aboard the Solar and Heliospheric Observatory (SOHO) between1995 and 2015. For a statistical analysis, onset times have been determined forthe events and the proton energy spectra were derived and fitted with a powerlaw. As a result, a list of 42 SEP events with protons accelerated to above 500MeV measured with the EPHIN instrument onboard SOHO is presented. Thestatistical analysis based on the fitted spectral slopes and absoluteintensities is discussed with special emphasis on whether or not an event hasbeen observed as GLE. Furthermore, a correlation between the derived intensityat 500 MeV and the observed increase in neutron monitor count rate has beenfound for a subset of events.