The Pacific Decadal Precession and Its Relationship to Tropical and Extratropical North Pacific Decadal Variability in the CMIP6 Models

Recent research uncovered evidence of a quasi-decadal mode of climate variability, termed the Pacific Decadal Precession (PDP), a counterclockwise progression of an atmospheric pressure anomaly dipole from a north-south oriented phase to an east-west oriented phase around the North Pacific at low frequencies. In particular, the north-south phase of the PDP, resembling the North Pacific Oscillation, is hypothesized to be partially maintained by Central Pacific sea-surface temperature anomalies, and thereby related to Central Pacific ENSO (CP-ENSO) events. Evidence for a relationship between CP-ENSO events and the north-south phase of the PDP would have significant implications for understanding the dynamics of the PDP. Indeed, accurate projections of the PDP can have significant implications for seasonal and interannual predictions of North American climate conditions such as drought and pluvial cycles in the Pacific Northwest. This study applies statistical methods outlined in previous literature, namely extended empirical orthogonal function analysis on extended boreal winter 850 hPa geopotential height anomalies, to pre-industrial control runs from the Coupled Model Intercomparison Project Phase 6 (CMIP6) output to characterize how the models generally represent the spatial structure of the PDP. The characteristic pattern of the PDP and the amplitude of the north-south phase derived from individual model output and their ensemble-mean is then compared to how the models simulate CP-ENSO events. Findings indicate that most models have trouble replicating the full precession and period of the PDP, particularly the east-west phase of the phenomenon. Comparisons are then made between the degree to which the model accurately captures tropical Pacific decadal variability (both in space and frequency) and its representation of the PDP. These differences are tied directly to central tropical Pacific SST variability and ENSO variability in the models. Implications of these findings on the fidelity of future climate projections of Pacific decadal climate variability in the models will also be discussed.