Lastovicka, J., and P. Mlch. “Solar Cycle Effect on Oscillations in the Period Range of 2-20 Days in the F Region of the Ionosphere”. Annals of Geophysics 39, no. 4 (November 25, 1996). Accessed November 27, 2021. https://www.annalsofgeophysics.eu/index.php/annals/article/view/4018.