Gleissberg (101yr) and de Vries (208yr) solar periodicities match precessional boundary resonances P/256 and P/128 within 3%

Analysis of SILSO v2.0 sunspot records (1749–2026) and the Steinhilber et al. (2012) cosmogenic isotope reconstruction (9,400 years) yields two periodicities matching harmonics of the 25,772-year precessional cycle: the Gleissberg period (~101 yr) matches P/256 = 100.7 yr within 0.3%, and the de Vries/Suess period (~208 yr) matches P/128 = 201.3 yr within 3.3%. Grand minima spacings additionally match P/64 (396 yr) and P/32 (705–805 yr cluster) within 2–5%.

Assumptions

- The precessional period (25,772 yr) is physically coupled to the galactic boundary crossing timescale — this is proposed but not proven
- The period matches are not coincidental results of testing many P/N fractions
- The cosmogenic isotope reconstruction accurately reflects solar activity variations over 9,400 years

Open Questions

- How many P/N fractions were tested? If many, Bonferroni correction applies and the matches may not be significant.
- Does the EPICA 800,000-year ice core record show the same periodicity pattern?
- Is there a proven physical mechanism connecting the precessional cycle to the galactic magnetic boundary?

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