The scale of cyclic variations in extreme ultraviolet and X-ray radiation from the Sun according to data about the ionospheric E-layer and the results of direct measurements during different activity cycles
Aa. Nusinov et al., The scale of cyclic variations in extreme ultraviolet and X-ray radiation from the Sun according to data about the ionospheric E-layer and the results of direct measurements during different activity cycles, GEOMAG AER, 39(6), 1999, pp. 39-44