The Composition of the Solar Wind

Authors: F.M. Ipavich
Reference: Spring AGU Conference 2000


We review the status of composition measurements of the present-day solar wind. These measurements are of interest because they reflect the composition of the solar photosphere, and hence of our solar system.

Fractionation processes (both solar and instrumental) can result in an observed elemental compostion that differs from the composition of the solar wind at its origin in the solar atmosphere. These fractionation processes are much less important for isotopes of a given element. Fractionation effects for elements are tradtionally organized in terms of an element's First Ionization Potential (FIP), with the ratio of low-FIP elements to high-FIP elements being larger in the solar wind than in available measurements from the photosphere and from meteorites. The degree of this enhancement is known to depend on the type of solar wind being sampled. Although the reported values of the magnitude of this enhancement have decreased somewhat over the years, they remain larger in low speed solar wind than in coronal hole-associated solar wind, which in turn remains somewhat larger than 1. The enhancement observed in the solar wind is almost always smaller than that found in solar energetic particle populations.

The relatively high mass resolution and large collection power of recent instruments has significantly expanded the number of elements and isotopes for which abundances are available for the in-situ solar wind. We review a sample of such recent results from the CELIAS/MTOF sensor on the SOHO spacecraft.

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Last Update: April 2, 1999, James Weygand