The eight-year solar cycle during the Maunder minimum

The Maunder minimum (1645–1715 AD) is a representative grand solar minimum with highly depressed sunspot activity and coincident with the “Little Ice Age” on the Earth. Owing to the limited data quality of the currently used solar activity proxies, the cyclic solar activity variations during the Maunder minimum still need to be explored. By analyzing the red equatorial aurorae recorded in Korean historical books in the vicinity of a low-intensity paleo-West Pacific geomagnetic anomaly, we find clear evidence of an eight-year solar cycle during the Maunder minimum. This result provides a new data source on solar activity and a key constraint to theoretical solar dynamo models. It helps understand the generation mechanism of grand solar minima and the solar-terrestrial relations during the Maunder minimum.