Influence of interplanetary coronal mass ejections on the peak intensity of solar energetic particle events

We study whether the presence of coronal mass ejections (CMEs) in interplanetary space (ICMEs) affects the maximum intensity of solar energetic particle (SEP) events. We compute the maximum intensity of 175-315 keV electron and 9-15, 15-40, and 40-80 MeV proton fluxes measured during the prompt component of 147 western SEP events observed near Earth throughout solar cycle 23. When using in situ observations to determine the presence and location of preceding ICMEs during SEP events, we find that, over the ensemble of events, those observed either within a preceding ICME or when a preceding ICME is beyond the observer's location have, on average, larger peak intensities than the events observed in absence of ICMEs. The few events observed when an Earth-directed ICME is located between the Sun and the observer tend to have lower 9-15 and 15-40 MeV proton peak intensities than the events without preceding ICMEs; the differences are not significant for 175-315 keV electron peak intensities. When using coronagraph observations to determine the presence of preceding CMEs, we find that, over the ensemble of events, those events (Case P) occurring within 24 h after the launch of a CME from the same active region as the primary CME generating the SEP event tend to have higher peak intensities than those events (Case NP) occurring without a preceding CME. The differences between the average peak intensities of these two event cases (P and NP) are smaller when we exclude events observed when a prior ICME is already located at or beyond Earth.