  The hydrogen Lyman-alpha plays a dominant role in the radiative energy
transport in the lower transition region, and is important for the stud- ies of
transition-region structure as well as solar wind origin. We investigate the
Ly-alpha profiles obtained by SUMER in coronal holes and quiet Sun. In a subset
of these observations, also the Hi Lyman-beta, Si iii, and O vi lines were
(quasi-) simultaneously recorded. We find that the distances between the two
peaks of Ly-alpha profiles are larger in coronal holes than in the quiet Sun,
indicating a larger opacity in coronal holes. This difference might result from
the different magnetic structures or the different radiation fields in the two
regions. Most of the Ly-beta profiles in the coronal hole have a stronger blue
peak, in contrast to those in quiet-Sun regions. Whilst in both regions the
Ly-alpha profiles are stronger in the blue peak. Although the asymmetries are
likely to be produced by differential flows in the solar atmosphere, their
detailed formation processes are still unclear. The radiance ratio between
Ly-alpha and Ly-beta decreases towards the limb in the coronal hole, which
might be due to the different opacity of the two lines. We also find that the
radiance distributions of the four lines are set by a combined effect of limb
brightening and the different emission level between coronal holes and quiet
Sun.
