Illustration of time-slit velocity maps and velocity differences at scan position 3. Top: time-slit velocity maps of scan position number 3. The scale is clipped at ±2.5 km s⁻¹ for the three spectral lines, Hα (left), He I D₃ (centre), Ca II IR (right), for the selected points in the field of view. Velocities have been calculated applying the centre-of-gravity method to the upper 20% of each spectral line. Bottom: velocity differences calculated between pairs of lines as indicated in the label of each plot. In this case, the scale es clipped at ±1 km s⁻¹. The vertical black line in the bottom line is used to display the temporal variations of the velocities in Fig. 9.