  The moss is the area at the footpoint of the hot (3 to 5 MK) loops forming
the core of the active region where emission is believed to result from the
heat flux conducted down to the transition region from the hot loops. Studying
the variation of Doppler shift as a function of line formation temperatures
over the moss area can give clues on the heating mechanism in the hot loops in
the core of the active regions. We investigate the absolute Doppler shift of
lines formed at temperatures between 1 MK and 2 MK in a moss area within active
region NOAA 11243 using a novel technique that allows determining the absolute
Doppler shift of EUV lines by combining observations from the SUMER and EIS
spectrometers. The inner (brighter and denser) part of the moss area shows
roughly constant blue shift (upward motions) of 5 km/s in the temperature range
of 1 MK to 1.6 MK. For hotter lines the blue shift decreases and reaches 1 km/s
for Fe xv 284 {\AA} (~2 MK). The measurements are discussed in relation to
models of the heating of hot loops. The results for the hot coronal lines seem
to support the quasi-steady heating models for non-symmetric hot loops in the
core of active regions.
