1. Voyager Observations of Anomalous Cosmic Rays in the Outer Heliosphere
ICRC
8/15/11
A. C. Cummings, E. C. Stone, F. B. McDonald, B. C. Heikkila, N. Lal, W. R. Webber

2. McComas and Schwadron (2006) picture
V2 ACR intensities would be expected to be higher than those at V1 because closer to source region along flanks of shock. See also Kota 2007 for similar picture with source on tail of shock. V2
high
intensity V1
low

3. TSP
TSP
ACR
TSP
ACR
ACR
GCR
GCR
GCR
TSP spectrum normalized at low energies to estimate TSP contributions at higher energies
Thanks to LECP team for low-E Ions, He, and O data

4. a= -0.70; b= -3.14; E0= 3.27 MeV

5. V1 H V1 H V2 H TSP intensities very similar at V1 and V2 until 2010
0.035
0.35
1.0
1.6
TSP intensities very similar at V1 and V2 until 2010
Recent V1 decrease due to transient of leakage out heliosphere?
Not observe expected energy dependence

6. V1 H TSPs dominate through mid 2007
1.8
TSPs dominate through mid 2007
Then ACRs begin appearing above ~3 MeV
Do increasing ACRs mask a decrease in TSPs at 2 to 3 MeV?
2.2
3.0
4.6
6.2

7. V1 H
V1 H
Higher energy ACRs appear earlier as expected

8. Large ACR intensity increase at V2 over last year; small decrease at V1
V2 intensity > V1 intensity
Region of strong gradient AU at V2?
Latitudinal, longitudinal, dynamical?

9. 07 08 09 10 11 12 V1 ACR O intensities peaked in 2010
~25% decease at higher, ~15% at lower energy
Particles could be leaking out heliopause
Not expect if ACR source near heliopause
ACR O intensities now ~2x higher at V2 than at V1 and at an all-time high.
ACR source higher in south than in north?
ACR source at shock on flanks or tail?
(McComas and Schwadron; Kota)
Recovery from transient that began ~ may contribute to the V2 intensity increase
Origin of V2 decrease not known

10. 07 08 09 10 11 12 V1 ACR O intensities peaked in 2010
~25% decease at higher energy, ~15% at lower
Particles could be leaking out heliopause
Not expect if ACR source near heliopause
ACR O intensities now ~2x higher at V2 than at V1 and at an all-time high.
ACR source higher in south than in north?
ACR source at shock on flanks or tail?
(McComas and Schwadron; Kota)
Recovery from transient that began ~ may contribute to the V2 intensity increase
Origin of V2 decrease not known

11. Evidence for 2008 transient but not in 2009
No significant change in plasma at time of 2010 increase
Vsw
2008
2009
2010
2011
Richardson et al.

12. V2 No consistent correlation with unipolar (U) or sector (S) regions
V2 > V1 is expected if ACR source is on the flanks (McComas et al., Kota)
Vsw
2008
2009
2010
Burlaga e al. 2011

13. V2 ACR H and He intensities have exceeded V1 ACR intensities by ~40% in several energy bands in early 2011.
Now approaching 100%

14. Free Escape Boundary V2 V1
Kota & Jokipii ICRC 2011

15. ACRs intensity at V1 has decreased from intensity peak in 2009
Summary
ACRs intensity at V1 has decreased from intensity peak in 2009
Suggests source is not beyond 112 AU in nose region
Larger ACR O decrease at higher energies
Suggestive of diffusive loss out of nearby heliopause
Transient effect at V1?
ACR intensity rapidly increased at V2, is now up to ~2x V1
V2 is 22 AU closer to sun than V1
V1 is on nose meridian, V2 is closer to flank
Consistent with source on flanks on at tail (McComas & Schwadron; Kota)
Latitudinal or dynamical origin?