SUMER observations of solar transition region structures and dynamics

Several raster scans of the UV/EUV spectrometer SUMER (Solar Ultraviolet Measurements of Emitted Radiation) on SOHO (the Solar and Heliospheric Observatory of ESA and NASA) in quiet-Sun regions were used to study the region between the chromosphere and the corona, i.e., the transition region with a temperature range between approximate to 30 000 K and 400 000 K. A typical SUMER scan of 100 raster steps with the 300"-long slit leads to 30 000 pixels containing spectral information and it is, therefore, a good statistical base. The aim was to calculate probability distributions of line intensities and shifts, and to study the relationship between intensities and shifts. These signatures were determined for emission lines with various formation temperatures across the transition region. Results show that intensity contrasts as well as Doppler shifts depend on the formation temperature and peak around 100 000 K, which is also the region with the strongest relation between line intensities and shifts. (C) 2002 COSPAR. Published by Elsevier Science Ltd. All rights reserved.