Solar Cycle Variation of Suprathermal Heavy Ion Composition and Spectra
during Quiet Times near 1 AU
Abstract
We report on the annual variation of quiet-time suprathermal ion
composition and spectral properties for C-Fe using Advanced Composition
Explorer (ACE)/Ultra-Low Energy Ion Spectrometer (ULEIS) over the energy
range 0.3 MeV/nuc to 1.28 MeV/nuc from 1998 through 2020. This extends
the work of Desai et al. (2006) and Dayeh et al. (2009, 2017) to cover
Solar Cycle 23’s rising phase through Solar Cycle 24’s declining phase.
With 5 additional years of data, we show that the number of quiet-time
hours strongly anti-correlates with the Sunspot Number (SSN) at better
than the -0.9 level. We also show (1) a clear ordering of the cross
correlation between abundance (normalized to O) and SSN as a function of
solar wind M/Q; (2) the slope of X/O’s abundance as a function of Fe/C
decreases with increasing M/Q; and (3) discuss the trend of annual
spectral indicies with respect to Oxygen’s spectral index as a function
of solar cycle and M/Q. The contrast between our abundance and spectral
index results suggests that the source from which suprathermal ions are
drawn or accelerated varies with solar activity and is tied to each
element’s chemistry, but he acceleration mechanism that governs the
spectral shape does not.