M.E. Wiedenbeck, JPL/Caltech Thanks to: the ACE/ULEIS &SIS Teams and the STEREO/LET, SIT, & SEPT Teams 9 June 20101ACE/SOHO/STEREO/Wind Workshop

9 June 20102ACE/SOHO/STEREO/Wind Workshop Longitudinal Spread of SEPs from 3 He-rich Events single spacecraft studies looked at longitudinal difference between point of SEP observation and site of the flare from which the particles were thought to have been released complicated by the fact that 3 He-rich events are often associated with small x-ray flares, so making the association is sometimes difficult one of the goals of STEREO is to investigate the characteristics of individual SEP events from multiple points of observation Longitude Number of Events Reames σ ~ 40°

9 June 20103ACE/SOHO/STEREO/Wind Workshop STEREO Launch ACE ULEIS & SIS points: individual Bartels rotation curve: 7-rotation averages Fraction of Time with 3 He Present Near 1 AU – Solar Cycle Variation the first several years of the STEREO mission have characterized by very low solar activity the number of 3 He-rich events available for study has been small, but the chance of confusing different events is significantly reduced 3 He-rich SEP activity has sharply increased in the past 6 months

Solar Maximum 3 He Observed with ACE: Solar Minimum--Solar Maximum Comparison at solar maximum there are lots of 3 He-rich events at solar minimum 3 He-rich events are rare—provides a better opportunity to correlate events between different spacecraft without (much) confusion 9 June 20104ACE/SOHO/STEREO/Wind Workshop Solar Minimum small 3 He-rich event

9 June 2010ACE/SOHO/STEREO/Wind Workshop5 3 He rich Events at ACE, STEREO-Ahead, and STEREO-Behind AHEAD BEHIND ACE ±20° ticks indicate days with 3 He-rich SEPs present Data sources: STEREO-A & -B: LET, MeV/nuc ACE: ULEIS, MeV/nuc

9 June 2010ACE/SOHO/STEREO/Wind Workshop6 3 He rich Events at ACE, STEREO-Ahead, and STEREO-Behind an event observed on both STEREO spacecraft and on ACE AHEAD BEHIND ACE ±20°

9 June 20107ACE/SOHO/STEREO/Wind Workshop Event Observed over a Wide Range of Heliographic Longitudes 3-4 Nov 2008 event the STEREOs were located ±41° from ACE electrons were observed at all three spacecraft using STEREO/SEPT and ACE/EPAM 3 He and heavy ions with enhanced Fe/O were observed at STEREO-B and ACE the lack of an ion detection at STEREO-A might be due to sensitivity limitations results discussed in Wiedenbeck et al. 2010, SW12 Proceedings

9 June 2010ACE/SOHO/STEREO/Wind Workshop8 3 He rich Events at ACE, STEREO-Ahead, and STEREO-Behind events in the first quarter of 2010 AHEAD BEHIND ACE ±20°

9 June 2010ACE/SOHO/STEREO/Wind Workshop9 Increased Rate of 3 He-rich Events in Early 2010 see numerous events, some of which overlap in time In some cases there are approximate time coincidences (e.g., Feb 13-15), but often there are not these 3 He-rich events have very low intensity compared to some events observed near solar maximum; with larger events, establishing that different spacecraft are observing the same event should be easier

9 June 2010ACE/SOHO/STEREO/Wind Workshop10 Improving Reliability of Event Associations between Different Spacecraft A variety of event characteristics can be compared to improve confidence in associations between events detected at different spacecraft: timing of onset timing of release from the Sun (onset time corrected for transit time based on velocity dispersion) fluence details of time-intensity profile energy spectra anisotropy associated impulsive electron events ion composition ( 3 He/ 4 He, Fe/O, etc.) Useful comparisons with solar context: jets associated with the flare event longitudinal spread of open field from active region from PFSS model Larger events are needed to take advantage of many of these comparisons.

9 June 2010ACE/SOHO/STEREO/Wind Workshop to Sun STEREO/LET Observations of 3 He-rich SEPs at Solar Minimum search for events in low energy ( MeV/nuc) interval to improve ratio of He signal to background from ACRs & CIRs. events are typically very small to confirm event identification, look for 1) 3 He spectrum that falls with increasing energy, 2) anisotropy, 3) velocity dispersion, and/or 4) coincident electron event STEREO-A SEPT electron measurements 11