The Pacific Decadal Oscillation, Revisited

Abstract

The Pacific decadal oscillation (PDO), the dominant year-round pattern of monthly North Pacific sea surface temperature (SST) variability, is an important target of ongoing research within the meteorological and climate dynamics communities and is central to the work of many geologists, ecologists, natural resource managers, and social scientists. Research over the last 15 years has led to an emerging consensus: the PDO is not a single phenomenon, but is instead the result of a combination of different physical processes, including both remote tropical forcing and local North Pacific atmosphere-ocean interactions, which operate on different time scales to drive similar PDO-like SST anomaly patterns. How these processes combine to generate the observed PDO evolution, including apparent regime shifts, is shown using simple autoregressive models of increasing spatial complexity. Simulations of recent climate in coupled GCMs are able to capture many aspects of the PDO, but do so based on a balance of processes often more independent of the tropics than is observed. Finally, it is suggested that the assessment of PDO-related regional climate impacts, reconstruction of PDO-related variability into the past with proxy records, and diagnosis of Pacific variability within coupled GCMs should all account for the effects of these different processes, which only partly represent the direct forcing of the atmosphere by North Pacific Ocean SSTs.

Interannual and Decadal Variability in Tropical Pacific Sea Level

“…In this region, interannual variability is dominated by El Niño/Southern Oscillation (ENSO) events. On longer time scales a combination of low-frequency ENSO and PDO are important [14]. We find that DSL variability is often underestimated in CMIP5 pre-industrial control simulations, suggesting that climate models may not reproduce the full range of potential regional SLR.…”

Global-mean surface temperature variability: space–time perspective from rotated EOFs

“…Current understanding of the physical origin of the PDO was reviewed by Newman et al (2016). In a paper entitled "ENSO-forced variability of the Pacific decadal oscillation", Newman et al (2003) showed that variability on both interannual and decadal time scales of the PDO can be reproduced when tropical ENSO was introduced as a forcing term in an AR1 model.…”

Spatial Patterns of Sea Level Variability Associated with Natural Internal Climate Modes

“…The correlation coefficients for PDO-IPO and IPO-NINO3.4 indices (8-year low-passed) are both 0.88 over the period of 1900(Han et al 2014aZhang and Church 2012). Given their high correlations on decadal timescales, it has been suggested that the IPO may not be confidently treated as an independent climate mode to ENSO decadal variability (e.g., Trenberth et al 2007) or that the PDO is a statistic mode rather than a physical mode with a single mechanism (see review by Newman et al 2016). For consistency, unless specified otherwise, we will use the term PDO hereafter to represent decadal ENSO variability, PDO and IPO.…”

“…2.1). While it is the leading empirical mode, the PDO is not a single physical mode of climate variability because it results from the combination of three groups of processes: (1) variability associated with the Aleutian low due to stochastic whether noise and remote forcing from the tropics (largely ENSO), (2) ocean memory and (3) decadal variability of Kuroshio-Oyashio currents induced by westward-propagating oceanic Rossby waves (see review paper by Newman et al 2016). Given that different processes may dominate the PDO during different decades, the PDO-associated SST, wind, and thus sea level patterns may have different manifestations.…”