PACIFIC DECADAL OSCILLATION (PDO) |
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Pacific Decadal Oscillation (PDO)The Pacific Decadal Oscillation (PDO), discovered by Hare who studied the relationship between salmon migration in Alaska and Pacific Ocean temperatures, and defined by Mantua et al. (1997). It refers to cyclical variations in sea surface temperatures in the Pacific Ocean. The amplitude of this climate pattern varies irregularly on interannual to interdecadal timescales. According to NCAR’s Climate Data Guide, the PDO is defined as the dominant pattern (EOF) of monthly sea surface temperature anomalies in the North Pacific, north of approximately 20°N, after removing the global mean and the seasonal SST cycle. Source: NCAR – Climate Data Guide. The PDO index is defined as the principal component (PC) of the monthly sea surface temperature variability in the North Pacific (from 20°N for the period 1900–1993). Positive values correspond to negative SST anomalies in the central and western North Pacific (extending east of Japan) and positive SST anomalies in the eastern North Pacific (along the west coast of North America). Overall, the spatial pattern of the PDO resembles that of ENSO. The major distinction between the PDO and ENSO is their timescale: while ENSO is primarily interannual, the PDO is decadal. The PDO explains about 27% of the variance of North Pacific SST anomalies from 1870 to 2014, making it one of the dominant modes of basin-wide climate variability. Studies also suggest characteristic cycles of approximately 20–30 years, along with longer oscillations between 50–70 years. Source: NCAR – Climate Data Guide. PhasesThe PDO consists of a warm phase and a cold phase. Phase shifts can have significant implications on global climate, affecting cyclone activity, changes in the Jet stream trajectory, droughts and floods around the Pacific basin, marine ecosystem productivity, and global temperature patterns. The PDO can intensify or diminish ENSO impacts depending on its phase. If ENSO and PDO are in the same phase, it is believed that the impacts of El Niño/La Niña may be strengthened or weakened. According to the UK Met Office, positive phases of the PDO tend to favor periods of accelerated global warming due to reduced vertical mixing of cold deep waters, while negative phases are associated with relative cooling or a slowdown in observable warming. Source: Met Office – PDO. Positive Phase: Above-average temperatures from the Alaskan coast to the equator characterize the warm phase. Warm waters form a 'horseshoe'-shaped pattern around a core of cooler-than-average water. PDO impacts depend partly on its alignment with ENSO; if the cycles are in opposite phases, the effects weaken. However, when both PDO and ENSO are in the positive phase—meaning ENSO would be in an El Niño phase. Example Negative Phase: Unlike the positive phase, below-average temperatures from the Alaskan coast to the equator indicate the negative phase of the PDO. The region of above-average SST in the central Pacific is surrounded by below-average temperatures near the North American continent. Example Some Climate Anomalies
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• UCAR – Climate Data Guide
https://climatedataguide.ucar.edu/climate-data/pacific-decadal-oscillation-pdo-definition-and-indices
• NOAA / NCEI – PDO Index
https://www.ncei.noaa.gov/access/monitoring/pdo/
• Met Office – PDO explanation
https://weather.metoffice.gov.uk/learn-about/weather/oceans/pacific-decadal-oscillation
The Pacific Decadal Oscillation (PDO) and the Southern Oscillation/El Niño (ENSO) influence sea surface temperature, sea-level pressure, and surface winds in similar ways. The fundamental difference between PDO and ENSO is the time scale: while ENSO events typically persist between 6 and 18 months, PDO signatures can last for decades, usually between 20 and 30 years.
The PDO mainly affects the North Pacific but also alters circulation behavior near the equator. ENSO, on the other hand, operates more strongly at low latitudes, but its secondary effects extend into the North Pacific. This behavior was described in Mantua et al. (2001). The positive phase of the PDO tends to generate oceanic and atmospheric patterns similar to those observed during El Niño events, while the negative phase favors patterns similar to La Niña. Example.
Several studies investigate how the PDO modulates the effects of ENSO. Although part of the results are contradictory or depend on the region analyzed, some works have identified a consistent relationship. The classic study by Gershunov and Barnett (1998) shows that the PDO can amplify or reduce ENSO teleconnections. Thus, the climatic signal of El Niño is usually more intense when the PDO is positive, and the La Niña signal tends to be stronger when the PDO is negative.
More recent studies reinforce this modulation. For example, research published in Wang et al. (2014) shows that El Niño events occurring during the positive phase of the PDO generally produce stronger precipitation and temperature anomalies in various regions of the planet. Other studies indicate that the strength of the ENSO–Asian monsoon relationship also varies depending on the phase of the PDO, as observed in recent studies in Asia.
These results suggest that the PDO does not control ENSO but alters the ocean–atmosphere “background state,” influencing how ENSO anomalies propagate globally. In positive PDO phases, the North Pacific presents warmer conditions, which favor an atmospheric response typical of El Niño. During negative phases, conditions favor responses typical of La Niña. Therefore, the interaction between PDO and ENSO depends on the prevailing oceanic and atmospheric configuration, and their effects vary across continents and latitudes.
The table below shows this relationship.
| DATE | PDO Threshold: 0.0 |
ONI Threshold: 0.5 |
RELATIONSHIP |
|---|---|---|---|
| 2024-10 | Negative | -3.8000 | Neutral | -0.2600 | Neutral |
| 2024-11 | Negative | -3.1300 | Neutral | -0.3700 | Neutral |
| 2024-12 | Negative | -2.0300 | Negative | -0.5300 | Intensified Negatively |
| 2025-01 | Negative | -1.2800 | Negative | -0.5900 | Intensified Negatively |
| 2025-02 | Negative | -1.4000 | Neutral | -0.3800 | Neutral |
| 2025-03 | Negative | -1.1200 | Neutral | -0.1800 | Neutral |
| 2025-04 | Negative | -1.1500 | Neutral | -0.0900 | Neutral |
| 2025-05 | Negative | -1.6600 | Neutral | -0.1100 | Neutral |
| 2025-06 | Negative | -2.6200 | Neutral | -0.1100 | Neutral |
| 2025-07 | Negative | -4.1600 | Neutral | -0.1900 | Neutral |
| 2025-08 | Negative | -3.2000 | Neutral | -0.3200 | Neutral |
| 2025-09 | Negative | -2.3300 | Neutral | -0.4500 | Neutral |
| SOUZA, C. A. de; REBOITA, M. S. Ferramenta para o Monitoramento dos Padrões de Teleconexão na América do Sul. Terrae Didatica, Campinas, SP, v. 17, n. 00, p. e02109, 2021. DOI: 10.20396/td.v17i00.8663474 |
