Clette, Frédéric ; Vaquero, José M. ; Cruz Gallego, María ; Lefèvre, Laure

published in Proceedings of the IAU, 14 issue Symposium A30, pp. 156-159 (2020)

Abstract: Due to its unique 400-year duration, the sunspot number is a central reference for understanding the long-term evolution of solar activity and its influence on the Earth environment and climate. Here, we outline current data recovery work. For the sunspot number, we find historical evidence of a disruption in the source observers occurring in 1947–48. For the sunpot group number, recent data confirm the clear southern predominance of sunspots during the Maunder Minimum, while the umbra-penumbra ratio is similar to other epochs. For the Dalton minimum, newly recovered historical observations confirm a higher activity level than in a true Grand Minimum.

Keyword(s): Sunspots ; Solar cycle ; Historical data
DOI: 10.1017/S174392131900396X
Links: link