Elemental composition variations in the solar wind: Comparisons between Ulysses and ACE within different solar wind regimes

The elemental composition of the solar wind is likely established at the base of the corona, a conclusion based on the observed dependence of solar wind abundances on the first ionization potential (FIP) of the elements. Although the plasma conditions within the ecliptic solar wind are highly variable, the elemental composition is less so, and is an indicator of the nature of the solar source. In particular, coronal hole (CH, fast) solar wind tends to have less of a FIP enhancement of the low -FIP elements (e.g., Fe, Mg, Si) than interstream (IS, slow) solar wind. The elemental composition of coronal mass ejections (CMEs) is more variable, but tends to be similar to IS composition. The question we address here is how much does the average composition of the different solar wind regimes vary over the course of the solar cycle and between solar cycles. For the most recent solar cycle, which included the unusually deep and prolonged solar minimum (2006 - 2010) Lepri et al. (2013) have shown measurable drifts in the elemental composition within solar wind regimes using data from the Advanced Composition Explorer (ACE) Solar Wind Ion Composition Spectrometer (SWICS). In contrast, von Steiger and Zurbuchen (2011) have shown using Ulysses SWIC data that the composition of the very fast polar coronal hole flow has remained constant. Here, we extend the Lepri et al. ecliptic analysis to include data from Ulysses, which allows us to expand the analysis to the previous solar cycle (1990 - 2001), as well as check consistency with their recent solar cycle results. (Note that although Ulysses was nominally a polar mission, it spent considerable time at low latitudes as well.) A major driver for this investigation is the Genesis Mission solar wind sample analysis. Namely, was the solar wind sampled by Genesis between late 2001 and early 2004 typical of the solar wind over longer time scales, and hence a representative sample of the long-term solar wind, or was it somehow unique? Our initial findings show that the low-FIP composition measured by ACE/SWICS during the Genesis collection period was, within systematic error, in agreement with that measured by Ulysses (when it was at latitudes < |20°|). Specifically, the measured CH, IS, and CME Fe/O abundances differed between the ACE and Ulysses by 17%, 6.9% and +17%, respectively. The overall solar wind Fe/O ratio differed by only -3.6%. We will give further details on this comparison, and discuss variations in elemental composition over the course of the solar cycle and between cycles.