Spectral shape of solar particle events at energies above 100 MeV/n

High energy particles of galactic and solar origin crossing a spacecraft affect experiment performance in space. At time scales of tens of minutes, galactic cosmic-ray (GCR) energy fluxes vary of a few percent at most. Conversely, solar energetic particle (SEP) fluxes may vary of several orders of magnitude during the same periods of time. In order to study accurately the effects of the incident solar particles on future space experiments, a good knowledge of particle energy distribution during the whole duration of SEP events is necessary. We report here the parameterization of proton and helium energy spectra observed during SEP events of different intensity at energies above 100 MeV/n. We benefit of both data inferred at the top of the atmosphere from ground neutron monitor observations and recent measurements gathered by the PAMELA cosmic-ray experiment carrying a magnetic spectrometer in space.