Physics
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmsh43a1647a&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #SH43A-1647
Physics
7514 Energetic Particles (2114), 7536 Solar Activity Cycle (2162), 7845 Particle Acceleration, 7857 Stochastic Phenomena (3235, 3265, 4475), 7863 Turbulence (4490)
Scientific paper
We have surveyed the spectral and compositional properties of suprathermal heavy ions during quiet times from 1995 January 1 to 2007 December 31 using Wind/STEP and ACE/ULEIS at energies between 0.04 and 2.56 MeV/nucleon. We find that: (1) Quiet-time Fe/O and C/O abundances are correlated with solar cycle activity, reflecting corresponding values measured in solar energetic particle (SEP) and interplanetary (IP) shock events during solar maximum, and those measured in the solar wind (SW) and corotating interaction regions (CIRs) during solar minimum conditions. (2) The 3He/4He ratio lies in the 3% - 8% range during the quiet times of 1998 - 2004 with an average 3He abundance of ~27.4%. This ratio drops to 0.3% - 1.2% during 2005 - 2007 and the 3He quiet-time abundance drops to ~5%. (3) All heavy ion species exhibit suprathermal tails between 0.04 - 0.32 MeV/nucleon with spectral indices ranging from ~1.27 to 2.29. These tails sometimes extend above ~2 MeV/nucleon with Fe spectra rolling over at lower energies than those of CNO. (4) The suprathermal tail spectral indices of heavier species (i.e., Fe) are harder than those of the lighter ones (i.e., CNO). These indices do not exhibit a clear solar cycle dependence and for ~50% of the time, they deviate significantly from the 1.5 value. These compositional observations provide evidence that even during the quietest times in interplanetary space, the suprathermal population (3He and C-through-Fe) consists of ions from different sources whose relative contributions vary with solar activity. The heavy ion energy spectra exhibit suprathermal tails with variable spectral indices that do not exhibit the spectral index of 1.5 predicted by some recent models.
Al-Dayeh M.
Desai Mihir I.
Dwyer Joesph R.
Mason Glenn M.
Mazur J. E.
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