A Search for Interplanetary Energetic Particle Events from Solar Posteruptive Arcades

Abstract

While the E > 10 MeV ions observed in gradual solar energetic particle (SEP) events in space are attributed to accleration at shocks driven by coronal mass ejections (CMEs), it has been suggested that such SEPs may also result from acceleration in the magnetic reconnection of coronal arcades following CMEs. The arcade SEPs could escape the corona along open field lines and form an additional contribution to an observed gradual SEP event. However, arcade components of SEP events would be difficult to distinguish from fluctuations in an acompanying population of shock SEPs. Most CMEs are not fast enough to drive shocks, but they always produce open coronal field lines leading to the arcade events. We examine large solar soft X-ray arcades and metric noise storms in the western hemisphere which should be favorable for the production of arcade SEP events observed at 1 AU. We find about 5 cases possilbly associated with IMP-8 24 to 28 MeV SEP events, which appear to be shock acclerated. However, we also find 30 arcades, 14 in active regions and 16 outside active regions, with no detectable SEP increases, suggesting that those arcadew were not sources of escaping SEPs. This result provides evidence against the possibility of nonshock coronal contributions to gradual SEP events.