Top panel: SUMER detector image taken at 15:48 UT. The region between the horizontal solid lines was used to produce the spectrum during the event. The same region was taken from the spectrum obtained later at 15:56 UT (shown in Fig. 7) to produce the reference spectrum. Bottom panel: the spectrum during the event is shown with a solid line, while the reference spectrum is shown with a dotted (red in the online version of the paper) line. “W” next to the line, e.g. “N v W”, denotes the blue wing of the line.