Stephen et al,
Further to the interesting discussion on non-equilibrium processes in the corona, I unashamedly advertise two relevant pieces of my own work:
1. the DIPER package which handles these (among other) things,
http://www.hao.ucar.edu/modeling/haos-diper/
(see the image displayed at this url).
2. a paper discussing the analytical evolution of atomic systems based upon an eigen-expansion. It enables one to understand how multi-level systems evolve and corrects some misconceptions in the literature:
"Understanding the time dependence of atomic level populations in evolving plasmas", Judge, P. G., Journal of Quantitative Spectroscopy and Radiative Transfer, 92, p. 479-510 (2005).
Best wishes
Philip Judge HAO.