temperature along a plume, we assume that the geometry of a plume does not change during its evolution, and then project it onto the density and temperature maps deduced from the line ratio of the Si[viii]{} line pair and the Mg[ix]{} line pair, respectively [@Wilhelm:2006; @Wilhelm:etal:2009]. Consistent with the previous results, the plumes are denser and cooler than the interplume regions. The Doppler shift measurements, we deduced from the O[vi]{} lines based on the method outlined in @Wilhelm:etal:1998.

SUMER scanned the relevant region from April 7 01:01 UTC to April 8 12:19 UTC continuously moving from west to east. To compare these data with the EUVI observations of a 3D plume, we need to first rotate the Sun from the EUVI observations to the time at which SUMER scanned it. An example is shown in the density map in the upper panel of Figure \[fig:sumer\_dentem\]. The inclined lines are the projected positions of three plumes. The vertical line corresponds to the position of the SUMER slit at April 8 01:00 UTC. Consider plume 1, the plotted location was obtained by first rotating the Sun to this time and then projecting plume 1 onto the density map. From Figure \[fig:sumer\_dentem\] we 