Nevanlinna, H., and C. Sucksdorff. “Impulse in Global Geomagnetic "Secular variation", 1977-1979”. Journal of Geophysics 50, no. 1 (October 22, 1981): 68-69. Accessed September 16, 2025. https://journal.geophysicsjournal.com/JofG/article/view/197.