Evolution of Sunspot Magnetic Fields from the Measurements at the BST-2 Telescope of the Crimean Astronomical Observatory in Solar Cycle 24

Abstract: The evolution of the averaged values of the sunspot magnetic fields with a strength of ≥1500 G has been studied based on long-term spectral observations of the splitting of the Zeeman components of the Fe I 630.2-nm line at the Solar Tower Telescope BST-2 of the Crimean Astrophysical Observatory for the period from 2010 to 2018 (4771 measurements in total). It was found that, in contrast to the Wolf numbers, the averaged magnetic field of sunspots does not vary significantly with time. Moreover, it very slightly increases and reaches its peak by the end of the 24th solar cycle. The results support the important role of “negative” magnetic pressure in the formation of sunspots at small depths near the Sun’s surface.