Synchronized interdecadal variations behind regime shifts in the Pacific Decadal Oscillation

Abstract

Interdecadal climate variability over the North Pacific is investigated using a reconstructed 298-year-long annual Pacific Decadal Oscillation Index during 1700–1997. Here, we show that its interdecadal component can be decomposed into the bi-decadal (~ 20 years), the tri-decadal (~ 30 years), and the multi-decadal variations (~ 60 years) through bandpass filtering. The phase reversals of the bi-decadal and the tri-decadal variations were synchronized throughout the data, while the synchronization of the bi-decadal and the multi-decadal variations was maintained during 1780–1880 and 1920–1997. Monte Carlo simulation reveals that this synchronous temporal structure is statistically significant and could not occur from random processes. We further demonstrate that these three phase-locked variations play an important role in the regime shifts in the North Pacific, both during the data period (1700–1997) and thereafter. The bi-decadal variation, which is self-sustained through the North Pacific mid-latitude air–sea interaction, is also found to be possibly linked to the lunar nodal cycle. Moreover, the tri-decadal and the multi-decadal variations, whose periods are approximately 1.5 and 3 times longer than that of the bi-decadal variation, may be linked to the bi-decadal variation through nonlinear process. This simple relationship could largely contribute to understanding and predicting the interdecadal climate variability.