M.E. Wiedenbeck, JPL/Caltech

Thanks to:the ACE/ULEIS &SIS Teams andthe STEREO/LET, SIT, & SEPT Teams

9 June 2010 1ACE/SOHO/STEREO/Wind Workshop

9 June 2010 2ACE/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

Longitude

Reames 1999

2σ ~ 40°

9 June 2010 3ACE/SOHO/STEREO/Wind Workshop

STEREO Launch

ACE ULEIS & SIS

points: individual Bartels rotation curve: 7-rotation averages

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

Solar Maximum

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

9 June 2010 4ACE/SOHO/STEREO/Wind Workshop

Solar Minimum

small 3He-rich event

9 June 2010 ACE/SOHO/STEREO/Wind Workshop 5

3He rich Events at ACE, STEREO-Ahead, and STEREO-Behind

AHEAD

BEHIND

ACE ±20°

ticks indicate days with 3He-rich SEPs present

Data sources:•STEREO-A & -B: LET, 2.3-3.8 MeV/nuc•ACE: ULEIS, 0.2-1 MeV/nuc

9 June 2010 ACE/SOHO/STEREO/Wind Workshop 6

3He 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 2010 7ACE/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

9 June 2010 ACE/SOHO/STEREO/Wind Workshop 8

3He rich Events at ACE, STEREO-Ahead, and STEREO-Behind

•events in the first quarter of 2010

AHEAD

BEHIND

ACE ±20°

9 June 2010 ACE/SOHO/STEREO/Wind Workshop 9

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

9 June 2010 ACE/SOHO/STEREO/Wind Workshop 10

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.

9 June 2010 ACE/SOHO/STEREO/Wind Workshop

to Sun

STEREO/LET Observations of3He-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

STEREO-A SEPT electron measurements

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