Takalo, Jouni J. “Temporal Distribution of Solar Cycle 24 Sunspot Groups: Comparison to Cycles 12-23”. Annals of Geophysics 64, no. 1 (March 15, 2021): DM107. Accessed April 24, 2024. https://www.annalsofgeophysics.eu/index.php/annals/article/view/8562.