The Evolution of Heavy Ion Abundances with Solar Activity
arXiv:2504.18092 · doi:10.1051/0004-6361/202554299
Abstract
When observed at 1 AU, slow solar wind is typically considered to have originated in source regions with magnetic topologies that are intermittently open to the heliosphere. Fast wind is typically considered to have originated in source regions that are continuously open to the heliosphere eg coronal holes. The evolution of the solar wind helium abundance (AHe) with solar activity is likely driven by the evolution of different solar wind source regions. Separating the solar wind into fast and slow for each element based on its characteristic speed derived in Alterman et al. (2025) we quantify the evolution of helium and heavy element abundances with solar activity. We show that AHe strongly correlates with sunspot number; in slow and fast wind the average non-transient solar wind AHe is limited to 51% of its photospheric value; slow wind heavy element abundances evolve significantly with solar activity; fast wind heavy element abundances do not; the correlation coefficient with sunspot number of elemental abundances for species heavier than He monotonically increases with increasing mass; and the correlation coefficients between the in situ observations and the normalized sunspot number are stronger than those using the unnormalized sunspot number. We infer that the sunspot number is a clock timing the solar cycle but not the driver of the physical process underlying the evolution of these abundances with solar activity; this underlying process is likely related to the energy available to accelerate the solar plasma from the chromosphere and transition region or low corona into the solar wind; and differences between the evolution of slow and fast solar wind abundances are similarly related to the energy available to accelerate the elements at these heights above the Suns surface.
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