Latitude Dependence of Element Abundances in the Slow Solar Wind

Details Latitude Dependence of Element Abundances in the Slow Solar Wind Latitude Dependence of Element Abundances in the Slow Solar Wind

Dec 2002

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufmsh21a0515v&link_type=abstract

American Geophysical Union, Fall Meeting 2002, abstract #SH21A-0515

Other

2162 Solar Cycle Variations (7536), 2164 Solar Wind Plasma, 2169 Sources Of The Solar Wind, 7507 Chromosphere, 7509 Corona

Scientific paper

Since 1992 the Ulysses spacecraft orbits the Sun on a high-inclination orbit with an inclination of 80 degrees to the heliographic equator. The first orbit, in 1992--98, took place around solar minimum and revealed a highly ordered state of the heliosphere with large high-speed streams poleward of about 30 degrees heliolatitude, emanating from the relatively cool polar coronal holes, separated by a band of slow solar wind at low latitudes. In the slow wind the abundances of elements with a low first ionisation potential (FIP) such as Fe, Mg, and Si, are found to be enhanced over the solar values relative to the high-FIP elements by a significant factor of 2--5. On the other hand, this FIP enrichment factor was found to be less than a factor of two, but still significantly larger than one, in the polar high speed streams. On the second orbit, which is now taking place around the maximum of solar cycle 23, slow solar wind is found at all heliolatitudes, interspersed with fast streams from fragmented coronal holes and from coronal mass ejections, also at all latitudes. Using data from the SWICS sensor on Ulysses, we have found that the strength of the FIP fractionation factor appears to depend on the heliographic latitude, even if we restrict ourselves to unequivocal slow solar wind. The strongest FIP enrichments are found at low latitudes, which can also be observed from the ecliptic plane, but they are becoming increasingly weaker at higher latitudes. This was particularly evident during the second fast latitude scan in 2000/01. We will present the observational data and discuss their possible implications for the underlying coronal structure, specifically in the framework of the Fisk model. In this model the slow solar wind is pictured as made up from a sequence of prevoiusly closed magnetic loops that are emptied onto open, migrating field lines. The strength of the FIP fractionation of the loop material may expected to be a function of loop parameters such as length, temperature, or age, so therefore a systematic variation of the FIP fractonation factor may reveal a dependence of these parameters on heliographic latitude.

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