Solar Physics Division Meeting 2000, June 19-22
Session 13. Solar Corona
Oral, Chair: D. A. Biesecker, Thursday, June 22, 2000, 8:30-10:00, 10:30-11:00am, Forum

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[13.07] Properties of Solar Polar Coronal Hole Plasmas Observed Above the Limb

G.A. Doschek, U. Feldman, J.M. Laming (NRL)

We discuss nonthermal motions, line-of-sight emission measures, and relative element abundances as a function of height in the solar polar coronal holes. The data pertain to the upper transition region and coronal regions of the atmosphere at heights ranging from the solar limb to about 150\arcsec\ above the limb. The spatial resolution is 1\arcsec. The physical quantities are derived from spectral line intensities and profiles obtained by the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer on the Solar and Heliospheric Observatory (SOHO) spacecraft. The line width information is important for wave theories of coronal heating. We find that the electron temperature in the polar holes increases with height above the limb, that the emission measure distribution of plasma at line-of-sight heights less than 60\arcsec\ peaks at a temperature of about 9 x 105 K, and that nonthermal motions sometimes, but not always, increase slightly with height above the limb. When observed, these increases level off above the limb at about 120\arcsec. We speculate that the line width increases with height above the limb may be a manifestation of the fast solar wind. Finally, we find that increases of a Mg VI/Ne VI line ratio with height above the north polar limb are probably due to the increase of electron temperature with height, and not due to a relative element abundance variation caused by the first ionization potential (FIP) effect. This work was supported by NASA SR&T Grant W-19,329 and by the ONR/NRL Research Option, Solar Magnetism and the Earth's Environment.


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