We have analyzed IRIS spectral and slit-jaw observations of a quiet region
near the South Pole. In this article we present an overview of the
observations, the corrections, and the absolute calibration of the intensity.
We focus on the average profiles of strong (Mg ii h and k, C ii and Si iv), as
well as of weak spectral lines in the near ultraviolet (NUV) and the far
ultraviolet (FUV), including the Mg ii triplet, thus probing the solar
atmosphere from the low chromosphere to the transition region. We give the
radial variation of bulk spectral parameters as well as line ratios and
turbulent velocities. We present measurements of the formation height in lines
and in the NUV continuum, from which we find a linear relationship between the
position of the limb and the intensity scale height. We also find that low
forming lines, such as the Mg ii triplet, show no temporal variations above the
limb associated with spicules, suggesting that such lines are formed in a
homogeneous atmospheric layer and, possibly, that spicules are formed above the
height of 2 arc sec. We discuss the spatio-temporal structure near the limb
from images of intensity as a function of position and time. In these images,
we identify p-mode oscillations in the cores of lines formed at low heights
above the photosphere, slow moving bright features in O i and fast moving
bright features in C ii. Finally, we compare the Mg ii k and h line profiles,
together with intensity values of the Balmer lines from the literature, with
computations from the PROM57Mg non-LTE model developed at the Institut
d'Astrophysique Spatiale and estimated values of the physical parameters. We
obtain electron temperatures in the range of ∼8000 K at small heights to
∼20000 K at large heights, electron densities from 1.1×1011 to
4×1010 cm−3 and a turbulent velocity of ∼24km/s.Comment: Accepted for publication in Solar Physic
