Correlation study of some solar activity indices in the cycles 21 - 23

TL;DR

This study analyzes the correlations between various solar activity indices and F10.7 across solar cycles 21-23, revealing cyclic variations in their relationships with periods around 5.5 years.

Contribution

It provides a detailed analysis of the linear and polynomial correlations between multiple solar indices and F10.7 over three solar cycles, highlighting cyclic patterns in their relationships.

Findings

Correlation coefficients show cyclic variations with ~5.5-year periods.

Most indices have near-linear regressions with F10.7 except near activity extrema.

The study covers six solar indices across three solar cycles.

Abstract

The correlation coefficients of the linear regression of six solar indices versus F10,7 were analyzed in solar cycles 21, 22 and 23. We also analyzed the interconnection between these indices and F10,7 with help of the approximation by the polynomials of second order. The indices we've studied in this paper are: Wolf numbers - W, 530,3 nm coronal line flux - F530, the total solar irradiance - TSI, Mg II UV-index 280 nm core-to-wing ratio, Flare Index - FI and Counts of flares. In the most cases the regressions of these solar indices versus F10,7 are close to linear except the moments of time near to the minimums and maximums of 11-year activity. For the linear regressions we found that the values of correlation coefficients Kcorr(t) for the indices versus F10,7 and W show the cyclic variations with periods approximately equal to the to half length of 11-year cycle - 5,5 years approximately.