Abstract
Measuring the long-term variability of solar EUV/UV irradiances is needed for e.g. studying the Sun’s influence on space weather, satellite drag and for solar studies. However, direct measurements remain limited, making predictive modelling crucial. We have found linear correlations between EUV daily spectral irradiances obtained from SOHO/CDS and SDO/EVE and solar proxies of activity, such as the F10.7, F30 cm radio fluxes and the Mg II index over several solar cycles, analysing data from 1998 until 2024. We confirm previous findings in that the F30 and the Mg II indexes are better, and that the variations increase with the formation temperature of the lines; the transition region lines show very little variations, except the hydrogen and helium lines. A code to predict the EUV irradiances of the main lines is provided. Relatively good agreement between the CDS and EVE irradiances is found, but significant differences with historical measurements are found in some EVE lines, especially at the longer wavelengths. Using the atomic data we made available in CHIANTI v.11 and the correlations with the proxies, we are building a new model to predict the lines and continua in the whole EUV spectral range covered by SDO/EVE.