  Aims. We analyse SUMER spectral scans of a large sunspot within active region
NOAA 10923, obtained on 14-15 November 2006, to determine the morphology and
dynamics of the sunspot atmosphere at different heights/temperatures. Methods:
The data analysed here consist of spectroheliograms in the continuum around
142.0 nm and in the Si iv 140.2 nm, O iii 70.3 nm, N iv 76.5 nm, and O iv 79.0
nm spectral lines. Gaussian-fitting of the observed profiles provides
line-of-sight velocity and Doppler-width maps. Results: The data show an
asymmetric downflow pattern compatible with the presence of the inverse
Evershed flow in a region within roughly twice the penumbral radius at
transition-region temperatures up to 0.18 MK. The motions, highly inhomogeneous
on small scales, seem to occur in a collar of radially directed filamentary
structures, with an average width less than the 1 Mm spatial resolution of
SUMER and characterised by different plasma speeds. Assuming that the flows are
directed along the field lines, we deduce that such field lines are inclined by
10 deg to 25 deg with respect to the solar surface.
