The Composition of the Solar Wind

The solar wind's charge state and elemental composition have been measured with the Solar Wind Ion Composition Spectrometers (SWICS) on Ulysses and ACE for a combined period of almost 25 years. This most extensive data set includes all varieties of solar wind flows and extends over more than one solar cycle. With SWICS the abundance of all charge states of He, C, N, O, Ne, Mg, Si, S, Ar, and Fe can be reliably determined (when averaged over sufficiently long time periods) under any solar wind flow conditions. Here we report primarily on results of our detailed analysis of the elemental composition and ionization states of the most unbiased solar wind from the polar coronal holes, and of the in-ecliptic wind sorted by solar wind speed. In particular, we will provide accurate values for the 20Ne abundance, and of S, Ca, and Ar as a function of solar wind speed. The systematics of the elemental composition and charge state distributions will be discussed.