11-Year solar cycle extreme ultraviolet and soft X-ray variations according to the ionospheric E-region data and results of direct measurements

A new solar-ionospheric index for representing both the relative variations of the short-wave ultraviolet (EUV) and soft X-ray emissions of the Sun is developed on the basis of investigating the ionospheric E-region as a global natural detector of solar radiation. (Values of EUV-variation for almost 5 cycles of solar activity were determined according to data of the global ionospheric network in the period 1947–1997). The new index is useful to be compared with others and to verify measurements of EUV radiation carried out by different equipment in various time periods as well as to compare different solar EUV-radiation models.