Presentation #201.07 in the session Suprathermal Particles and their Importance to Understanding Energetic Particles.
Gradual SEP events have the most impact on particle-induced space weather due to their high intensities of energetic ions. It has been difficult to predict SEP properties because we are still grappling with the origins of their high event-to-event variability. To reliably predict SEP events, it is essential to understand each factor that can play a role in the processes of SEP production so properties of a prospective SEP event can be predicted with confidence. Suprathermal ions play a critical role as a seed population in the SEP production by CME-driven shocks. Since a gradual SEP event is most intense at the beginning when the CME shock is still near the Sun (generally 2-5 Rs), the variability of near-Sun suprathermal particles is a crucial factor for understanding SEP variability. We present a study of enhanced suprathermal ion intervals measured by ACE/ULEIS during 2010 April — September, spanning 5 solar rotations. During this period of low solar activity, there were recurring solar wind and interplanetary magnetic field structures that were anchored by a long-lived north polar CH extension, as well as recurring equatorial coronal holes. We discuss the variation of suprathermal ion properties with the solar wind structure and the associated coronal source, and the implication of such variation in the near-Sun suprathermal particles.
Work supported by Basic Research Funds of the Office of Naval Research.