STEREO Views of Solar Energetic Particle Events: New Light on old Controversies

The launch of STEREO in early 2006 will provide the multipoint measurements of the solar wind and solar energetic particles (SEPs) that are complemented by stereo images of coronal processes and CMEs. As the STEREO spacecraft separate, their new points of view hold promise for resolving anumber of controversial questions about the acceleration and transport of SEP events. Examples include: (a) What is the relative contribution of shock and flare-accelerated particles? How does it happen that most large SEP events during solar cycle 23 appeared to include both shock and flare-accelerated particles in the same event? (b) Why is there typically a 5-10 minute delay between the electromagnetic signatures of SEP events and the inferred release of SEP electrons at the Sun based on their arrival times at Earth? (c) What are the seed particles for SEP events? It used to be assumed that CME-driven shocks accelerate solar wind, but composition studies suggest that several suprathermal populations are often more important. (d) How does shock acceleration vary from the nose of the shock to its flanks? Do such variations help account for the variability of SEP spectra? (e) What fraction of the CME kinetic energy goes into accelerated particles? Initial comparisons suggest that SEPs may extract as much as 10%-20% of the CME kinetic energy. This talk will discuss examples of how multipoint in situ and remote sensing observations from STEREO, along with near-Earth observations, can help resolve these and other issues. This work was supported by NASA under NAS5-00133, NAG5-12929, and NNG04GB55G.