Speaker
Description
$^{14}$C measurements from tree rings have been used by Usoskin et al. (2021, 2025, 2026) to reconstruct past solar activity cycles over three millenia from the year 1000 BCE onward. In Weisshaar et al. (2023, A&A 671, A87) we analysed a first data set covering the epochs of reconstructed activity minima and maxima of the reconstructed cycles between 971 and 1900 CE in order to determine whether there is evidence that the cycle is synchronized (by some kind of external regular “clock”, such as planetary tides) or its phase (with respect to the mean period) drifts, i.e. performs a random walk. Using a method originally suggested by D. O. Gough we found clear evidence of random walk and excluded synchronization at a high level of statistical significance. A similar result was found when only considering the minima and maxima based on the record of monthly sunspot numbers since 1749.
We have now extended the analysis to the full set of reconstructed cycles covering three millennia and confirm the previous result, i.e. random phase migration and no evidence for synchronization. In addition to the Gough method, we have also applied an autocorrelation technique which, in principle, could detect a mixture of synchronization and migration. Again, we find pure phase migration and no synchronization.
We also show that criticism of our previous work by Stefani et al. (Solar Physics 298, 83; 2023) is unfounded.