Variations of Ultraviolet Radiation in Solar Activity Cycles 22–24

Ultraviolet radiation fluxes in the MgII 280 nm and Lyman-alpha 121.6 nm lines, as well as the relative number of sunspots and the F10.7 radio emission flux were studied. It was found that the relative difference in the amplitudes of these activity indices changed significantly from solar minimum to maximum during the transition from the activity cycles 22 and 23 to cycle 24. In cycle 24, we examined the solar extreme ultraviolet radiation (EUV). Using the SDO/EVE archive of daily observations for 2010-2018, we created a time series of daily EUV radiation fluxes outside of flares. We also analyzed fluxes in the neutral helium lines (He I 58.4 nm and 53.7 nm) and ionized helium lines (He II 30.4 nm and 25.6 nm) during the activity cycle 24. Finally, we estimated how the intensity of these lines was changing with solar activity from the minimum to the maximum of the activity cycle 24. The study of double peaks at the maximum of solar activity, started by M.N.Gnevyshev [Gnevyshev, 1967], was continued. Double peaks were observed in all layers of the solar atmosphere (photosphere, chromosphere and corona).