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Session 1 - Chromosphere, Corona, Flares.
Display session, Friday, June 27
Ballroom B, Chair: Charles Kankelborg

[1.18] Observations of Doppler Shifts and Nonthermal Broadening in the North Polar Coronal Hole and Adjacent Quiet Sun

J. T. Mariska, H. P. Warren (NRL), K. Wilhelm (MPAe), P. Lemaire (IAS)

Coronal holes are thought to be the source of high-speed solar wind streams. It is, however, unclear at what height the outflow of material first becomes apparent. Using the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) experiment on the Solar and Heliospheric Observatory (SOHO\/), we have obtained observations in the north polar coronal hole, its boundary region, and the adjacent quiet Sun at wavelengths that cover emission lines of O VI at 1032 and 1038 ÅNe VIII at 770 Åand Mg X at 625 ÅThese lines are formed at temperatures of 0.3, 0.8, and 1.25 MK, respectively, and should thus help to determine the temperature at which outflows are first detected. For O VI and Mg X, we will report on Doppler shift measurements made relative to cooler chromospheric lines. Since there are no suitable emission lines from ions formed in the chromosphere for the Ne VIII line, we are only able to measure relative differences between the coronal hole and the adjacent quiet Sun. We will also report on the magnitude of the nonthermal broadening in these lines in the different solar regions.

This work was supported by a NASA SOHO\/ Guest Investigator Program grant.

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