Changed Relation between Solar 10.7-cm Radio Flux and some Activity Indices which describe the Radiation at Different Altitudes of Atmosphere during Cycles 21–23

Abstract

The correlation coefficients of the linear regression of six solar indices versus 10.7 cm radio flux F10.7 were analysed in solar cycles 21, 22 and 23. We also analysed the interconnection between these indices and F10.7 with help of approximation by polynomials of second order. The indices we have studied in this paper are: the relative sunspot numbers – SSN, 530.3 nm coronal line flux – F530, the total solar irradiance – TSI, Mg II 280 nm core-to-wing ratio UV-index, the Flare Index – FI and the counts of flares. In most cases the regressions of these solar indices vs. F10.7 are close to the linear regression except the moments of time near the minimums and maximums of the 11-year activity. For the linear regressions, we found that correlation coefficients Kcorr(t) for the solar indices vs. F10.7 and SSN dropped to their minimum values twice during each 11-year cycle.