To reconstruct the Pacific Decadal Oscillation a collection of 9 coastal tree-ring sites from Alaska to Oregon, and 2 PDSI gridpoints from Mexico were used. The individual tree ring chronologies were developed from mountain hemlock, Sitka spruce or Douglas Fir. The specific locations and site information are provided in a map and table.
Here is a photo of Greg Wiles at a coastal Alaskan mountain hemlock site.
A PDO reconstruction model with using principal components regression analysis using the Pacific Northwest tree sites and the Mexican PDSI sites explained 53% of the variance in the PDO in the 1900-1979 calibration period. This is shown in plots of the actual vs. estimated PDO index.
Two reconstructions for the PDO were developed, one covering the period from 1790-1979 and the other from 1700-1979.
Spectral analysis of the reconstruction reveals significant spectral modes at interannual to decadal scales of variation.
A comparison of plots of correlation fields between the instrumental PDO and SST and the reconstructed PDO show very good agreement which further indicate the success in using tree-rings to reconstruct the Pacific Decadal Oscillation Index..