Abstract :
Two decades ago it was discovered that emission lines from the solar transition region from the chromosphere to the corona are composed by two Gaussian components: a narrow core and a broad second component contributing up to 25% to the total intensity. New observations with SUMER/SOHO allow for the first time statistically significant results on the widths and Doppler shifts of the broad second components. Evidence will be presented that the two components of the line profile correspond to two radically different physical regimes.
Of course, the results for the dominant line core fit into the well known properties of transition region lines, e.g. the redshifts. In contrast, the second broad components, which occur only in the bright network, show different properties. Most striking is the fact that large parts of the network show blueshifts in the second components, while the core is redshifted at the same location.
The results suggest that the second component is formed in Gabriel-type coronal funnels and that these are heated in the same manner as open field regions, i.e. the solar wind. However, the analysis of the Doppler shifts shows that these funnels should not be magnetically open, but rather the footpoint regions of large coronal loops spanning across several network elements.
