Observations of Doppler Shifts in a Solar Polar Coronal Hole

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Abstract
Using observations from the Solar Ultraviolet Measurements of Emitted Radiation experiment flown on the Solar and Heliospheric Observatory spacecraft, we have measured Doppler wavelength shifts in the north polar coronal hole in the 1032 and 1038 Å emission lines of O VI and the 1036 and 1037 Å emission lines of C II relative to chromospheric emission lines. These observations were obtained on 1996 November 2 when the north polar coronal hole boundary extended southward to about 750'' (cos θ=0.65). Our measurements indicate the presence of average net redshifts in coronal holes at temperatures of less than 2.9×105 K. Measurements of systematic wavelength shifts in the Ne VIII resonance lines relative to the quiet Sun suggest a transition to average net outflows near 6.3×105 K in the coronal hole.