Ion energy spectra and abundance ratios are studied in 0.04-2 MeV/nucleon ion fluxes using ULEIS/ACE data during the solar minimum between solar cycles 23 and 24. The unique prolonged minimum of 2006-2009 permitted to select 35 quiet time periods when suprathermal ion fluxes originating from near-equatorial coronal holes (CH) were observed at 1 AU. The values of relative ion abundances indicate the presence of particle populations accelerated in different processes on the Sun and in the interplanetary space observed as suprathermal fluxes. The ratios of suprathermal C/O and Fe/O arising from coronal holes were found to correlate with their bulk solar wind ratios from CH (SWICS/ACE data) whereas 40-80 keV/nucleon 4He/O ratios were about two times higher than their bulk wind values. The 3He, 4He, Fe, C, and O ion energy spectra showed that ion intensities depend on solar wind speed and the fluxes were higher inside fast wind streams. The results obtained suggest that the bulk solar wind described by Maxwellian distribution appears to be the source of ions further accelerated to suprathermal energies thus forming the high energy solar wind tail. The ion spectra obtained here were fitted by power-law functions or combined power-law/exponential which suggests different mechanisms of acceleration.
|Journal||Proceedings of Science|
|Publication status||Published - 2015|
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