Synchronized interdecadal variations behind regime shifts in the Pacific Decadal Oscillation

摘要

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 (similar to 20 years), the tri-decadal (similar to 30 years), and the multi-decadal variations (similar to 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.