Patterns in solar activity over the first millennium CE

Abstract Radiocarbon ( 14 C) measurements are a powerful tool for reconstructing past solar activity and identifying extreme events caused by bursts of high-energy particles from the Sun. Such reconstructions improve understanding of long-term solar behaviour and the likelihood of hazardous particle events that are capable of disrupting modern technology. Here we present an annually resolved 14 C record spanning 1 to 970 CE comprising five newly measured and three existing series from tree rings. The record is analysed with methods that combine statistical modelling of the carbon cycle, data-adaptive decomposition of solar cycles, and probabilistic detection of rapid 14 C increases associated with energetic particle events. These analyses reveal four major intervals of reduced solar activity, two patterns in which the eleven-year cycle weakens then strengthens, and four candidate particle events in the years 14, 553, 675 and 954 CE.