  The spectral profiles of the coronal Ne viii line at 77 nm have different
shapes in quiet-Sun regions and coronal holes (CHs). A single Gaussian fit of
the line profile provides an adequate approximation in quiet-Sun areas, whereas
a strong shoulder on the long-wavelength side is a systematic feature in CHs.
Although this has been noticed since 1999, no physical reason for the peculiar
shape could be given. In an attempt to identify the cause of this peculiarity,
we address three problems that could not be conclusively resolved in a review
article by a study team of the International Space Science Institute (ISSI;
Wilhelm et al. 2011) : (1) The physical processes operating at the base and
inside of plumes as well as their interaction with the solar wind (SW). (2) The
possible contribution of plume plasma to the fast SW streams. (3) The signature
of the first-ionization potential (FIP) effect between plumes and inter-plume
regions (IPRs). Before the spectroscopic peculiarities in IPRs and plumes in
polar coronal holes (PCHs) can be further investigated with the instrument
Solar Ultraviolet Measurements of Emitted Radiation (SUMER) aboard the Solar
and Heliospheric Observatory (SOHO), it is mandatory to summarize the results
of the review to place the spectroscopic observations into context. Finally, a
plume model is proposed that satisfactorily explains the plasma flows up and
down the plume field lines and leads to the shape of the neon line in PCHs.
