Recent spectroscopic observations by the Solar and Heliospheric Observatory
(SOHO) have revealed the dynamic nature of even the 'quiet' sun. Spectral variability
data clearly show that dynamics in the solar upper atmosphere take place on
timescales shorter than those of ionisation relaxation. Accuracy in the interpretation of
diagnostic spectral data can only be maintained through detailed quantitative
modelling of the relevant atomic physics. In particular, dynamical plasma
models of the transition region and corona require matching dynamic atomic models to
underpin conclusions drawn from the spectral reduction. The inclusion of
important effects such as finite plasma electron density and the influence of metastable
states is essential to reduce the uncertainties associated with equilibrium
assumptions.
Some examples of observational evidence and theoretical atomic calculations are
given in this paper to illustrate these points.