Features of great minima in solar activity during the last 1000 years

Deep minima in solar activity, the so-called “reat minima” or “rand minima” occurred several times during the last 1000 years. Such prolonged periods of inactivity are confirmed by the past solar activity recorded in sunspot and auroral observations or tree rings and ice cores. These records show that such deep minima are fairly common in the long-term solar behavior, and are expected to occur again in the future. In this paper, we use the sunspot and auroral records of ancient Korea and China, and cosmogenic isotopes to examine the features of great minima in solar activity during the last 1000 years. The existence of great minima is clearly seen in the time distribution of historical data, in agreement with the variation of Δ14C content that increases during periods of great minima. Also, the sunspot and auroral records indicate that numerous auroral activities existed between the Spörer minimum and the Maunder minimum, and that the Spörer minimum occurred between ∼1410 and ∼1510 implying the duration of ∼100 years. In addition, we find that the longest period of solar inactivity during the last 1000 years occurred during the Spörer minimum where both sunspot and auroral records are scarcest among the great minima.