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

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?

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

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

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

Solar Cycle 23 and 24

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

ULEIS ~1 MeV/nuc Iron

ULEIS ~1 MeV/nuc Oxygen

Proton, Helium, Oxygen and Iron

Solar Wind Thermal Densities 2009-2010

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

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

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)