Effect of coronal holes on gradual solar energetic particle events

Gradual solar energetic particle (SEP) evnets are thought to be produced by shocks, which are usually driven by fast coronal mass ejections (CMEs). Shock strength and magnetic field configuration are of the most importance in shock acceleration. Conceptually, the two factors are both unfavorable for the production of SEPs in/near a coronal hole (CH). To answer the questions whether and how a CH affects a CME in producing SEP events, a statistical study is performed. By investigating 89 frontside fast halo CMEs, it is found that the occurrence probability of SEP events is relatively low when CMEs are near or fax away from CHs, and especially, big nearby CHs are evidently against the production of SEP events. Based on this statistical facts, how a nearby CH affects its CME neighbor in production of SEPs is discussed. Three possible interpretations are proposed.