General trends in the changes of indices of solar activity in the late XX - early XXI century

TL;DR

This study analyzes solar activity indices from cycles 22 to 24, revealing a significant decrease in sunspot numbers and magnetic field strength, with implications for understanding solar variability and its impact on solar irradiance.

Contribution

It provides new insights into the trends of solar activity indices and their interrelations, highlighting discrepancies with existing solar activity models.

Findings

SSN observed values decreased by 20-25% after 1990.

The solar constant TSI slightly increased during cycles 23-24.

Changes in sunspot characteristics do not fully align with predicted solar activity scenarios.

Abstract

The analysis of the observations of solar activity indexes SSN (NOAA Sunspot Numbers), the radio flux at a wavelength of 10.7 cm (F10.7) and the solar constant (TSI) during the cycles 22 - 24 is presented. We found a decrease of the observed values of the SSNobs which was calculated with SSNsyn (using regression relationships between SSN and F10.7) after 1990 year on 20 - 25% instead of 35%, as was previously assumed. The changes in characteristics of the most popular index, SSN, such as decrease in the number of sunspots, the reduction of the magnetic field in small and medium-sized spots are not in full compliance with the proposed scenario of solar activity predicted by radio flux F10.7 in the cycles 23 and 24, and cannot be fully explained by the influence on the SSN values of additional minimum of 50 - 70 year cycle. We have also showed that the observed changes of SSN lead to a slight increase of the solar constant TSI during the cycles 23 - 24 compared to the cycle 22.