Vol 19, No 7 (2019) / Bruevich

Long-term trends in solar activity. Variations of solar indices in the last 40 years

Elena Bruevich, Vasily Bruevich

Abstract

We analyze long-term variations of several solar activity indices (AIs) that have been measured over the last 40 years. With this goal, we study the AIs that characterize the fluxes from different areas in the 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 investigate the normalized variations of these indices in recent time in relation to their values which were calculated by considering radiation from the Sun in the radio range at a wavelength of 10.7 cm (F10.7 ) in 1950–1990. The analysis of time series, representing variations of the normalized AI (AIFF) in solar cycles 23–24, shows different trends exist for different indices in terms of their long-term behavior. We assume that variations of normalized International Sunspot Number (SSN), F530.3 and Flare Index, which have shown sharp decreases in the last 40 years, are 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).

Keywords


method: data analysis— Sun: activity indices

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DOI: https://doi.org/10.1088/1674–4527/19/7/90

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