A Mechanism for Pacific Interdecadal Resonances

Abstract

Pacific interdecadal variability (PIV) is an important large-scale climate phenomenon. There is growing evidence that PIV contains three spectral resonances: a decadal (13 ± 1-year) spectral peak, bidecadal (20 ± 5-year) resonance, and a pentadecadal (60 ± 10-year) resonance. Although much has been clarified about mechanisms behind PIV, there are still many open questions about the origin of these resonant modes (especially the pentadecadal mode). We describe dynamics in the Pacific basin by a toy (delayed oscillator) model that sheds light on the nature of these resonant peaks. The model suggests that unlike the bidecadal resonance, which results from local atmosphere-ocean coupling in the extratropics, the pentadecadal and possibly also decadal resonances result from atmospheric and oceanic teleconnections between the extratropics and tropics. We show that a tiny coupling between extratropics and tropics through the ocean tunnel is sufficient to trigger the pentadecadal oscillation in the Pacific basin. Our model also explains (a) the observed three-period locking between the bidecadal and pentadecadal modes and (b) the synchronization of anomalies in the central eastern tropics and central North Pacific with the opposite relative sign. We conclude that the role of oceanic teleconnections is probably underestimated in the current literature on PIV.