Abundance variations in the solar wind

Details Abundance variations in the solar wind Abundance variations in the solar wind

Jul 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995adspr..15q...3v&link_type=abstract

Advances in Space Research (ISSN 0273-1177), vol. 15, no. 7, p. (7)3-(7)12

Computer Science

41

Abundance, Coronal Holes, Ionization Potentials, Photosphere, Solar Atmosphere, Solar Wind, Variations, Helium, Magnesium, Mass Spectrometers, Oxygen, Solar Temperature, Solar Wind Velocity, Stellar Mass Ejection, Stellar Models, Ulysses Mission

Scientific paper

The solar wind (SW) allows us to probe the solar material in situ, particularly its composition, without the need to fly a spacecraft to inhospitably small heliocentric distances. However, it turns out that this plasma source is biased with respect to the photosphere. Elements with a low first ionization potential (FIP) are overabundant by a factor of 3-5 relative to high-FIP elements in the slow SW, but only by a factor of 1.5-2 in the fast streams emanating from coronal holes. It is thus important to have a good understanding of this FIP fractionation effect, which operates between the photosphere and the corona. Such a theory may improve on our understanding of the solar atmosphere and SW acceleration. We present SW measurements, concentrating on results of the SWICS mass spectrometer on Ulysses, which is currently sampling the SW on a highly inclined orbit. IN 1992/93, Ulysses was traversing a recurrent high-speed stream once per solar rotation, alternating with slow SW, providing a unique opportunity to compare these two SW types. We find a strongly positive correlation for low- to high-FIP element ratios (such as Mg/O) with coronal temperature, which in turn is anticorrelated with the SW speed. The correlation of these three parameters -- one chromospheric, one coronal, and one from the SW -- points at a common cause for their variations, and provides a challenge to theorists to model these three domains in an unified approach. Further, abundance variations found in the SW from coronal streamers and in coronal mass ejections are presented and discussed. Finally, we address the question of abundance variations within the fast streams, looking for abundance gradients with heliographic latitude.

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