EUV Spectral Variability and Non-Equilibrium Ionisation in the ‘Quiet’ Sun

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 solar plasma 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 levels is essential to reduce the uncertainties associated with equilibrium assumptions.