Recommendation for a set of solar EUV lines to be monitored for aeronomy applications

In two recent studies, Dudok de Wit et al. (2005) and Kretzschmar et al. (2006) have shown that the solar Ultra-Violet spectrum between 25 and 195 nm can be reconstructed from the observation of a set of 6 to 10 carefully chosen spectral lines. The best set of lines, however, is application dependent. In this study, we demonstrate that a good candidate for aeronomy applications consists of the following 6 lines: H I at 102.572 nm, C III at 97.702 nm, O V at 62.973 nm, He I at 58.433 nm, Fe XV at 28.415 nm and He II at 30.378 nm. The TRANSCAR model is used to quantify the impact of each individual line on the density, temperature and velocity profiles. Using a multidimensional scaling technique, we show how to select from this the best set of lines. Although this selection is motivated by the specification of the ionosphere, our set of lines is also found to be appropriate for reconstructing the variability of the solar spectrum between 25 and 195 nm.