Solar cyclic activity over the last millennium reconstructed from annual 14C data

Vol. 649
9. The Sun and the Heliosphere

Solar cyclic activity over the last millennium reconstructed from annual 14C data

This study builds on a recent annual resolution of 14C tree-ring data extending back about 1000 years ago, and it derives the behavior of the solar cycle for that period, almost tripling the temporal horizon available for studying the solar dynamo. The 14C production rate is referenced to Earth's current magnetic field using archeological reconstructions, and an elaborate cross-correlation procedure was adopted to convert the production rate to a sunspot number. To accomplish this, a truly novel feature of the multistep calculation uses space-based data from the AMS-02 measurement of low energy Galactic cosmic rays and in situ satellite measurements of solar magnetic activity to obtain a calibration for the open solar flux against ground-based neutron monitors and, through this, to pass to the sunspot number. The reconstructions were verified against the historical sequence since the first observations in the 17th century and ten were extended backwards. The resulting history of suns pot activity is fully cycle-resolved and should serve as a benchmark for all future modeling of solar activity, including solar-terrestrial relations.