BRADLEY, P. A. Further study of fOF2 and M(3000)F2 in different solar cycles. Annals of Geophysics, [S. l.], v. 37, n. 2, 1994. DOI: 10.4401/ag-4227. Disponível em: https://www.annalsofgeophysics.eu/index.php/annals/article/view/4227. Acesso em: 9 aug. 2022.