SUMER observations of Doppler shift in the quiet Sun and in an active region

The UV spectral lines formed at transition region temperatures in the solar atmosphere, show a prevailing redshifted emission. Using the Solar Ultraviolet Measurements of Emitted Radiation spectrometer flown on the Solar and Heliospheric Observatory spacecraft, we measure the amount of line shift as a function of the temperature for several spectral lines formed in the range between 10(4) and 10(6) K. We analyze spectrograms relative to the quiet Sun and to the active region NOAA 7946. The velocities derived are increasing from a redshift of similar to 0 km s(-1) at - 20000 K to 10 km s(-1) at 1.9 10(5) K for the quiet Sun, and to - 15 kill s(-1) at 10(5) K for the active region. At higher temperature an opposite behaviour is observed. In the quiet Sun a blueshift of similar to -2 km s(-1) is observed at the Ne vIII formation temperature (6.3 10(5) K), while in the active region, a blue-shifted value around -8 km s(-1) is observed for the same spectral line. The finding of blueshift in Ne vIII is due to the adoption of a new rest wavelength of 770.428 Angstrom. By 10(6) K the blueshift is similar to -10 km s(-1) in the active region as measured by Fe XII 1242.