The Composition of the Solar Wind in Polar Coronal Holes |
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Authors: | George Gloeckler Johannes Geiss |
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Institution: | (1) Department of Oceanic, Atmospheric and Space Sciences, University of Michigan, Ann Arbor, MI 48109-2143, USA;(2) Department of Physics, University of Maryland, College Park, MD 20742-0001, USA;(3) International Space Science Institute, Hallerstrasse 6, 3012 Bern, Switzerland |
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Abstract: | The solar wind charge state and elemental compositions have been measured with the Solar Wind Ion Composition Spectrometers
(SWICS) on Ulysses and ACE for a combined period of about 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 abundances 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 on results of our detailed analysis of the elemental composition and ionization states of
the most unbiased solar wind from the polar coronal holes during solar minimum in 1994–1996, which includes new values for
the abundance S, Ca and Ar and a more accurate determination of the 20Ne abundance. We find that in the solar minimum polar coronal hole solar wind the average freezing-in temperature is ∼1.1×106 K, increasing slightly with the mass of the ion. Using an extrapolation method we derive photospheric abundances from solar
wind composition measurements. We suggest that our solar-wind-derived values should be used for the photospheric ratios of
Ne/Fe=1.26±0.28 and Ar/Fe=0.030±0.007. |
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Keywords: | Sun: solar wind Sun: elemental composition Sun: isotopic abundance ratios |
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