Extreme Values of Sunspot Activity on a Long Time Scale

Abstract

The extreme levels of solar activity on time scales of 300–400 and 9000 years are considered. The total sunspot area \(AR\), a physical index of solar activity, has been estimated using the sunspot number reconstruction from Wu et al. (2018). The main study has been carried out precisely in terms of this index. The variations in solar activity at the epoch of the last 300–400 years represent fairly well its variations on time scales of the order of nine millennia. The maximum level of solar activity for the yearly averages is \(AR_{M}=2930\pm 400\) m.s.h. (millionths of the solar hemisphere). The upper limit for the daily values is \(AR_{M}=7500\pm 2200\) m.s.h. for the traditional sunspot areas corrected for the perspective distortion and \(AR_{OM}=11\,400\pm 3300\) m.s.d. (millionths of the solar disk) for the so-called ‘‘observed’’ areas—the sunspot projections onto the visible solar disk. The maximum yearly averages of the sunspot number \(SN_{M}=258\pm 38\) and the sunspot group number \(GN_{M}=12.3\pm 2.4\) have also been estimated; 11.3\({\%}\) of the time the solar activity is at an extremely high level; 8.5 and 4.5\({\%}\) of the time its level corresponds to the Dalton minimum or lower and an extremely low one, respectively. Thus, extremely high levels are more likely for solar activity than extremely low ones.