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Multipoint Observations of 3He-rich SEP Events Since the Launch of STEREO M.E. Wiedenbeck, JPL/Caltech Thanks to: the ACE/ULEIS &SIS Teams and the STEREO/LET, SIT, & SEPT Teams ACE/SOHO/STEREO/Wind Workshop
Longitudinal Spread of SEPs from 3He-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 3He-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 Number of Events Reames 1999 2σ ~ 40° Longitude ACE/SOHO/STEREO/Wind Workshop
Fraction of Time with 3He 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 3He-rich events available for study has been small, but the chance of confusing different events is significantly reduced • 3He-rich SEP activity has sharply increased in the past 6 months STEREO Launch ACE ULEIS & SIS points: individual Bartels rotation curve: 7-rotation averages ACE/SOHO/STEREO/Wind Workshop
3He Observed with ACE: Solar Minimum--Solar Maximum Comparison • at solar maximum there are lots of 3He-rich events • at solar minimum 3He-rich events are rare—provides a better opportunity to correlate events between different spacecraft without (much) confusion Solar Minimum Solar Maximum small 3He-rich event ACE/SOHO/STEREO/Wind Workshop
3He rich Events at ACE, STEREO-Ahead, and STEREO-Behind ticks indicate days with 3He-rich SEPs present AHEAD ±20° ACE • Data sources: • STEREO-A & -B: LET, 2.3-3.8 MeV/nuc • ACE: ULEIS, 0.2-1 MeV/nuc BEHIND ACE/SOHO/STEREO/Wind Workshop
3He rich Events at ACE, STEREO-Ahead, and STEREO-Behind • an event observed on both STEREO spacecraft and on ACE AHEAD ±20° ACE BEHIND ACE/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 • 3He 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 ACE/SOHO/STEREO/Wind Workshop
3He rich Events at ACE, STEREO-Ahead, and STEREO-Behind • events in the first quarter of 2010 AHEAD ±20° ACE BEHIND ACE/SOHO/STEREO/Wind Workshop
Increased Rate of 3He-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 3He-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 ACE/SOHO/STEREO/Wind Workshop
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 (3He/4He, 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. ACE/SOHO/STEREO/Wind Workshop
STEREO/LET Observations of • 3He-rich SEPs at Solar Minimum • search for events in low energy (2.3-3.8 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) 3He spectrum that falls with increasing energy, 2) anisotropy, 3) velocity dispersion, and/or 4) coincident electron event to Sun STEREO-A SEPT electron measurements ACE/SOHO/STEREO/Wind Workshop