What is the Pacific Decadal Oscillation?

The Pacific Decadal Oscillation (often referred to as the PDO), can strongly impact global weather and is important in long-range weather forecasting

What is the Pacific Decadal Oscillation – Introduction 

The Pacific Decadal Oscillation is a sea surface temperature (SST) climate cycle (or teleconnection) describing sea surface temperature anomalies over the Northeastern Pacific Ocean. The PDO can influence the weather conditions across North America with characteristic patterns occurring at different times of the year. 

The PDO oscillates between positive and negative phases. The positive phase is characterized by cool SSTs north of Hawaii and warmer than normal sea surface temperatures along the western coast of North America. (Figure 1). The negative phase is a mirror image with warm surface waters in the Central North Pacific and cooler than normal waters along the western coast of North America (Figure 2). 

Fig. 1: SST anomalies over the North Pacific Ocean during a positive Pacific Decadal Oscillation, showing a vast cool area north of Hawaii and warmer than normal waters near the North American coast
Fig. 2: SST anomalies over the North Pacific Ocean during a negative Pacific Decadal Oscillation, showing a vast warm area north of Hawaii and cooler than normal waters near the North American coast

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What is the Pacific Decadal Oscillation – Positive Phase Impacts 

Positive PDO Impacts – North American winter 

During the positive phase of the PDO in the northern hemisphere wintertime, the Southern and Eastern US is more likely to experience above normal temperatures, with below temperatures more likely in the West and Northwest (Figure 3). 

At the same time, the Northern Rockies and the Midwest are likely to be drier than normal, while Texas, the Gulf states, and the East are likely to be wetter than normal (Figure 4). 

Fig. 3: World Climate Service temperature anomaly probability map for a positive Pacific Decadal Oscillation in winter 
Fig. 4: World Climate Service rainfall anomaly probability map for a positive Pacific Decadal Oscillation in winter

Positive PDO Impacts – Asian winter 

During the positive phase of the PDO in the northern hemisphere wintertime, much of Asia is usually cooler than normal, with above normal temperatures more likely over India (Figure 5). 

At the same time, China and Japan are likely to be drier than normal, while India often has a winter that is wetter than normal (Figure 6). 

Fig. 5: World Climate Service temperature probability map for a positive Pacific Decadal Oscillation in winter
Fig. 6: World Climate Service rainfall probability map for a positive Pacific Decadal Oscillation in winter

What is the Pacific Decadal Oscillation – Negative Phase Impacts

Winter Negative PDO Impacts – North America 

During the negative phase of the PDO in wintertime, much of the lower 48 is usually warmer than normal. The West coast and the Northwest are normally colder than normal (Figure 7). 

At the same time, many parts of the US will see drier than normal weather, but there are some notable exceptions. During a negative PDO, winter rainfall is usually above normal for the Ohio and Tennessee Valleys as well as the Northern Rockies and Plains (Figure 8). 

Fig. 7: World Climate Service temperature probability map for a negative Pacific Decadal Oscillation in winter
Fig. 8: World Climate Service rainfall anomaly probability map for a negative Pacific Decadal Oscillation in winter

Negative PDO Impacts – Asian winter

During the negative phase of the PDO in the northern hemisphere wintertime, much of India and China is usually cooler than normal, But Japan has warmer than normal weather, especially in the North (Figure 9).

At the same time, Japan and Northwest China are usually wetter than normal, while Southwest China and much of India are usually wetter than normal (Figure 10).

Pacific Decadal Oscillation
Fig. 9: World Climate Service temperature probability map for a negative Pacific Decadal Oscillation in winter
Fig. 10: World Climate Service rainfall probability map for a negative Pacific Decadal Oscillation in winter

The World Climate Service provides a powerful data mining system which enables users to quickly explore the Pacific Decadal Oscillation, and many other indices, by phase for each month of the year, showing impacts on all the major weather parameters all around the globe.

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Pacific Decadal Oscillation and Long Range Forecasting

The Pacific Decadal Oscillation typically remains in a given phase for many years or even decades (Figure 11), but there can be some variation within a given decadal phase. 

Pacific Decadal Oscillation
Fig. 11: The PDO Climate Index variations since 1990

At the turn of the century, the PDO entered a long-term negative phase, but there was a positive hiatus between 2014 and 2019. Owing to the long-lasting phases of the PDO and their impact on Northern Hemisphere climates, this climate index is a very useful climate index for seasonal prediction.

What is the Pacific Decadal Oscillation – Conclusion 

The Pacific Decadal Oscillation is a cyclical variation of sea surface temperature anomalies over the North Pacific Ocean that influences weather patterns across large parts of Asia and North America. 

The Pacific Decadal Oscillation phases persist for many years which makes the PDO a prime consideration in seasonal forecasting. 

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