NAM logo, by David Le Conte

SUMER observations of doppler shift on quiet sun and active region

L. Teriaca, J.G. Doyle, R.Erdelyi, D. Banerjee

Observations of UV spectral lines formed at transition region temperatures in the solar atmosphere reveal a prevailing redshifted emission. By using the Solar Ultraviolet Measurements of Emitted Radiation spectrometer flown on the Solar and Heliospheric Observatory spacecraft, we measure the amount of line shift and non-thermal velocity as a function of temperature for several spectral lines formed in the range between 10⁴ and 10⁶K.

We analyse spectrograms relative to the quiet Sun and to the active region NOAA7946. The Doppler velocities derived increase from a redshift of ca. 0 km/s at 20,000K to 10 km/s at 1.9x10⁵K for the quiet Sun, and to ca. 15 km/s at 10⁵K for the active region.

At higher temperature an opposite behaviour is observed. In the quiet Sun a blueshift of about -2 km/s is observed at the Ne VIII formation temperature (6.3x10⁵K), while in the active region, a blue-shifted value around -8 km/s is observed for the same spectral line. By 10⁶K the blueshift is ca. -10 km/s in the active region, as measured by Fe XII 1242A.

Observations will be compared with the response to energy perturbation of a 1-D model of a semi-circular magnetic flux tube. The temporal evolution of the thermodynamic state of the loop is finally converted into C IV 1548.2A line profiles in non-equilibrium ionisation.

(For preprints, contact Robertus@sheffield.ac.uk)

Maintained by Ian Howarth