  The 11-year solar cycle is the dominant pattern of solar activity reflecting
the oscillatory dynamo mechanism in the Sun. Solar cycles were directly
observed since 1700, while indirect proxies suggest their existence over a much
longer period of time but generally without resolving individual cycles and
their continuity. Here we reconstruct individual cycles for the last millennium
using recent 14C data and state-of-the-art models. Starting with the 14C
production rate determined from the so far most precise measurements of
radiocarbon content in tree rings, solar activity is reconstructed in three
physics-based steps: (1) Correction of the 14C production rate for the changing
geomagnetic field; (2) Computation of the open solar magnetic flux; and (3)
Conversion into sunspot numbers outside of grand minima. Solar activity is
reconstructed for the period 971-1900 (85 individual cycles). 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 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 14C 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. A
new about 1000-year long solar activity reconstruction, in the form of annual
(pseudo) sunspot numbers with full assessment of uncertainties, is presented
based on new high-precision 14C measurements and state-of-the-art models, more
than doubling the number of individually resolved solar cycles.
