Yiğit, E., Kılçık, A., Elias, A.G., Dönmez, B., Özgüç, A., Yurchshyn, V., Rozelot, J.P., “Critical Frequencies of the Ionospheric F-1 and F-2 Layers During the Last Four Solar Cycles: Sunspot Group Type Dependencies“, Journal of Atmospheric and Solar Terrestrial Physics, 171, 157-163, 2018.