1000-year sunspot series

Results: Cyclic solar activity is reconstructed for the period 971-1900 (85 individual cycles) along with its uncertainties. This more than doubles the number of solar cycles known from direct solar observations. We found that lengths and strengths of well-defined cycles outside grand minima are consistent with those obtained from the direct sunspot observations after 1750.

The validity of the Waldmeier rule (cycles with fast rising phase tend to be stronger) is confirmed at a highly significant level. Solar activity is found to be in a deep grand minimum when the activity is mostly below the sunspot formation threshold, during about 250 years. Therefore, although considerable cyclic variability in ^14^C is seen even during grand minima, individual solar cycles can hardly be reliably resolved therein.

Three potential solar particle events, ca. 994, 1052 and 1279 AD, are shown to occur around the maximum phases of solar cycles. A new about 1000-year long solar activity reconstruction, in the form of annual (pseudo) sunspot numbers with full assessment of all known uncertainties, is presented based on new high-precision D14C measurements and state-of-the-art models, more than doubling the number of individually resolved solar cycles.

This forms a solid basis for new, more detailed studies of solar variability.