Long-term trends in the solar activity. Variations of solar indices in last 40 years (1812.11723v1)

Abstract: The analysis of long-term variations of several solar activity indices (AI) since in last 40 years has been performed. We studied the AI which characterize the fluxes from different areas in solar atmosphere. Our consideration of mutual correlations between the solar indices is based on the study of relationships between them in the period from 1950 to 1990. This period of time, covering activity cycles 19 -- 22, is characterized by relatively stable relations between the indices. We have studied the normalized variations of these indices in the recent time in relation to their values which have been calculated with help of the radiation of the sun in the radio range at a wavelength of 10.7 cm (F10.7) in 1950 -- 1990. The analysis of time series of variations of the normalized AI (AIFF) in solar cycles 23 -- 24 shows an existence of different trends for different indices in their long-term variations. We assume that variations of normalized SSN, F530.3 and Flare Index, which have shown a sharp decrease in last 40 years is possibly associated with a decrease in the intensity of large-scale magnetic fields in the photosphere (SSN) and in the corona (the coronal index and the Flare Index)