A Rogue Solar Energetic Particle Event at 0.33 AU: Importance of Interplanetary Structures in SEP Events

We study the interplanetary conditions during the occurrence of the most intense solar energetic particle (SEP) event observed by the MESSENGER spacecraft during the rising phase of solar cycle 24. Elevated electron intensities at MESSENGER (at 0.33 AU from the Sun) resulted from the confinement of energetic particles by two CME-driven shocks. This scenario is consistent with that proposed by Kallenrode and Cliver [3] to explain the most intense SEP events of a solar cycle. In analogy to the rogue ocean waves having unusually large amplitudes due to the superposition of two wave fields, these events were referred to as rogue SEP events. We compare the interplanetary conditions in the most intense event at MESSENGER with those observed in other rogue SEP events.