Belehaki, A., G. Moraitis, and I. Tsagouri. “On the Derivation of an Hourly Local Index to Define the Normal Ionosphere”. Annals of Geophysics 43, no. 1 (December 25, 2000). Accessed April 28, 2026. https://www.annalsofgeophysics.eu/index.php/annals/article/view/3629.