Space-time diagrams of the He I Doppler velocity based on single-component fits (top two panels) and the He I line depression (bottom two panels). Both quantities are displayed for a footpoint (top and third panel) and a loop top (second and bottom panel) position of an arch filament. These positions are marked in Fig. 3 by vertical red lines. The reference rotation image is the same as presented in Fig. 3. The blue arrow points out the individual arch filament in Figs. 13 and 14. The Doppler velocities were calculated assuming single- or dual-flow components when present.