Variability of EUV-spectra from the quiet upper solar atmosphere: Intensity and Doppler shift
1
Kiepenheuer-Institut für Sonnenphysik, Schöneckstr. 6, 79104 Freiburg, Germany
2
Institute of Astronomy, ETH-Zentrum, 8092 Zürich, Switzerland
3
Max-Planck-Institut für Aeronomie, Max-Planck-Str. 2, 37191 Katlenburg-Lindau, Germany
Corresponding author: A. Brković, alen@kis.uni-freiburg.de
Received:
15
May
2002
Accepted:
11
March
2003
We have studied SUMER and CDS time series of spectra and images of quiet-Sun regions at the solar disc centre. The data contain ultraviolet emission lines sampling temperatures of the chromosphere, transition region and corona. We find a high correlation between average net Doppler shifts and relative brightness variabilities of the studied lines (correlation coefficient of 0.92), suggesting a connection between the two quantities. The anti-correlation between differential emission measures and relative brightness variabilities is weaker (correlation coefficient of -0.78). We discuss the observed relationships on the basis of differential emission measures and linear wave calculations.
Key words: Sun: chromosphere / Sun: corona / Sun: transition region / Sun: UV radiation
© ESO, 2003