1. Suprathermal Particle Density Variations over the Solar Cycle
George Ho & Glenn Mason
35th ICRC2017
Busan, Korea

2. Introduction
ACE and other recent missions have provided multiple lines of evidence that energetic particles at 1 AU are accelerated out of the suprathermal ion population
Multiple investigations are characterizing the suprathermal population
In this paper we sort to answer these questions:
What are the long-term variation of supratheraml ion over solar cycle 24?
How does the suprathermal variation compare with the thermal particles?

3. Suprathermal Composition varies over Solar Activity
Flare suprathermals
Wiedenbeck et al., AIP CP, 2014

4. The mystery of huge heavy ion (Fe) variations in intensity
Peak intensities in shock events vary over a range of ~104
not explained by CME speed
not explained by shock acceleration models
not explained by solar wind number density which does not change nearly as much
Many researchers have suggested important role of suprathermal seed population
Mason et al., AIP CP781, 2005

5. Mewaldt et al., ICRC, 2015
ULEIS suprathermal densities of ~1500 days from each cycle when there were no significant solar proton event in progress
Mean densities in SC24 are lower by factor of 3.2 to 7.0 as compare to SC23
Mewaldt et al., ICRC 2015

6. Solar Cycle 23 and 24

7. Suprathermal Density Calculation
Survey multi-years of suprathermal ion data from ACE/ULEIS in both solar cycles
Examined the low energy channels from ACE/ULEIS for He, O, Fe
Export a flux number when have statistical significant (e.g. 1000)
Convert the flux number from multiple energy channel into an “integral density” number

8. ULEIS ~1 MeV/nuc Iron

9. ULEIS ~1 MeV/nuc Oxygen

10. Proton, Helium, Oxygen and Iron

11. Solar Wind Thermal Densities 2009-2010

12. Comparison between Solar Wind and Suprathermal Densities (2010)
Suprathermal (ULEIS)
Thermal (SWICS)

13. Comparison between Solar Wind and Suprathermal Densities (2009)
Thermal (SWICS)
Suprathermal (ULEIS)

14. Summary
We investigated the suprathermal particle densities throughout the the solar cycles and compare that with the solar wind
What are the long-term variation of supratheraml ion over solar cycles?
Suprathermal densities have a much broader distribution in Cycle 23 vs 24
As expected the suprathermal densities peak varies within the cycle
2009 suprathermal densities are unusually low as compare to any periods that we examined
How does the suprathermal variation compare with the thermal particles?
In general, the variation of the suprathermal density is large as compare to the solar wind (Fe, O, He)