Changes Over Time in The Relationship Between Solar Activity Indices

The results of the analysis of long-term changes in the relationship between solar activity indices for 1957-2022 are presented. For this purpose, the smoothed (using a 24-month filter) indices F10, F30, Ly-α, MgII, Ri and IG were used: the solar radio emission flux at the wavelengths of 10.7 and 30 cm, solar radiation in the Lyman-alpha line of hydrogen (121.567 nm), the ratio of the central part to the flanks in the magnesium emission band of 276-284 nm on the Sun, the international sunspot number and the ionospheric index, which is determined from ionospheric data as an analogue of the sunspot number. It was confirmed that the entire measurement period can be divided into the intervals 1957-1980, 1981-2012 and 2013-2022, in which the relationships between the solar activity indices are clearly different. In the interval 1957-1980, these relationships are stable over time, i.e. there is practically no linear time trend in the dependence of one solar activity index on another. In the 2013-2022 interval, such trends are usually significant. In this interval, the trend ΔIG(X) = IG - IG(X) is negative and significant for X = F10, F30, MgII, Ly-α, or Ri, where IG(X) is the average dependence of IG on X for this interval.