SUMER observations of transition region fine structures

Abstract

The SUMER (Solar Ultraviolet Measurements of Emitted Radiation) instrument on SOHO (Solar and Heliospheric Observatory) provides an opportunity to observe and study the solar transition region with high spatial and spectral resolution. We present new evidence to confirm that the emission from the quiet Sun at 2x 10⁵ K is dominated by cool loop-like fine structures which cluster across the chromospheric network boundaries. The electron density of these structures is found to be around 10¹⁰ cm^-3. The red-shifts in spectral line profiles and the non-thermal widths from lines formed at this temperature are found to be correlated with intensity. The properties of explosive events with irregular profiles are explored. A large jet-like structure is analysed. The results of our analysis are compared with recent predictions from numerical models.