Long-term studies of photospheric magnetic fields on the Sun Alexei A. Pevtsov, Luca Bertello, Yury A. Nagovitsyn, Andrey G. Tlatov and Valery V. Pipin J. Space Weather Space Clim., 11 (2021) 4 Published online: 22 January 2021 DOI: 10.1051/swsc/2020069