Monday

We discuss the fine structure of the Quiet Sun transition region, presenting an analysis based on high-resolution spectral observations from the Interface Region Imaging Spectrograph (IRIS). We present non-thermal widths obtained from Si IV, and discuss the variations due to the local electron temperature, which we estimate in different ways. The overall variations in the non-thermal widths are correlated with the intensity of the line, as found previously with e.g. HRTS and with IRIS by De Pontieu et al. (2018). We also measure, when the signal allows, electron densities from the O IV lines and estimate the spectroscopic filling factors, comparing the results with those obtained from HRTS. A better understanding of the transition region is important for the interpretation of observations from the Solar Orbiter SPICE spectrometer.