Discovery of the 5.7-Year Douglass Cycle: A Pioneer’s Quest for Solar Cycles in Tree-Ring Records

Abstract

Abstract. The astronomer A.E. Douglass is generally recognized as the founding father of dendrochronology. He studied tree rings in the search for evidence that solar variation (as seen in sunspots) is reflected in climate variation. He was convinced that his quest was successful. Analysis of some of his early data using Fourier decomposition and comparison of tree-ring periodograms with those based on known solar cycles suggests that the cycles he found may not exist or may not be of pure solar origin. The findings here reported suggest a much stronger influence of tides on the tree-ring records than commonly considered. Douglass's great merit as the pioneer of tree-ring dating in archeology and tree-ring-based climatology remains unaffected by the findings here presented.

Solar Activity and Lunar Precessions Influence Extreme Sea‐Level Variability in the U.S. Atlantic and Gulf of Mexico Coasts

“…Solar activity combined with lunar precessions has also been identified in the PDO index (Berger, 2011; Yasuda, 2009), that is, a connection from atmosphere to ocean variability. Lunar precession periodicity by itself can affect hot moments for flooding (Eliot, 2010; Haigh et al, 2011; Peng et al, 2019).…”

“…Outside the eastern seaboard of the United States, sea‐level variability and the susceptibility of coastal regions to flooding by tides have been linked to influences of lunar precessions at periodicities of 18.61 and 8.85 years and their first subharmonics of 9.305 and 4.425 years (Eliot, 2010; Haigh et al, 2011; Peng et al, 2019). Both lunar precessions (18.61, and 8.85 years, see supporting information for a description) and solar activity (10–11.5 year) have been described in dendrochronological records (Douglass, 1919, 1928, 1936), relating to ENSO history and the Pacific Decadal Oscillation (PDO) in the 20th century (Berger, 2011; Yasuda, 2009). Furthermore, solar activity seems to be correlated with the increased appearance of storm surges in the northern Adriatic Sea (Barriopedro et al, 2010; Zanchettin et al, 2009) and other European sites (Martinez‐Asencio et al, 2016).…”