IRIS observations for comparison with Fig. 6. (a) IRIS SJI at 2796 Å and the positions of artificial slices for time-distance diagrams. (b) Image of integrated intensity of the Mg II k line observed between 09:08:02 and 09:24:22 UT from left to right. (c) Time-distance diagram of IRIS SJI along slice S1, as marked in panel (a). The vertical dotted line represents the starting time of SUMER observations. Note that the traces of raster slit can be seen.