Satellites such as Jason-3 and the upcoming Sentinel-6 Michael Freilich measure the precise shape of the ocean's surface and how this surface changes through time. This helps scientists calculate ocean currents, identify climate trends, and improve weather forecasting models. A recently observed climate trend is the Pacific Decadal Oscillation.
Pacific Decadal Oscillation
The Pacific Decadal Oscillation (PDO) is a long-term ocean fluctuation of the Pacific Ocean. The PDO waxes and wanes approximately every 20 to 30 years. From ocean surface topography data, together with other ocean and atmospheric data, scientists can determine whether we are in a ‘cool’ phase or a ‘warm’ phase.
The 'cool' phase is characterized by a cool wedge of lower than normal sea-surface heights/ocean temperatures in the eastern equatorial Pacific and a warm horseshoe pattern of higher than normal sea-surface heights connecting the north, west and southern Pacific.
In the 'warm' or 'positive' phase, the west Pacific Ocean becomes cool and the wedge in the east warms. A ‘cool’ phase occurred from 1947 to 1976 (29 years), and a ‘warm’ phase from 1977 to 1999 (22 years). However, more recently, the ‘warm’ and ‘cold’ phases have been much shorter.
In 1999, we entered into a ‘cold’ phase for about 4 years (1999-2002) followed by a ‘warm’ phase that continued for 3 years. The phase was then neutral until 2007, when we entered into a ‘cold’ phase that lasted through 2013. The last PDO phase shift was in 2014, when it turned strongly positive (‘warm’).
The PDO is an active topic of research and satellite data, such as that from Jason-3, helps scientists observe and understand the phenomenon. For further information see our January 2000 press release and articles in the press.
FAQ about the Pacific Decadal Oscillation
Q. Who named the PDO and can you give me more indepth information?
A. The term PDO was coined in about 1996 by Steven Hare at the University of Washington. He, along with colleagues Nathan Mantua, Yuan Zhang, Robert Francis and Mike Wallace discovered the pattern as part of work on fish population fluctuations. They have given talks that provide excellent information.
Q. How does this affect climate?
A. The change in location of the cold and warm water masses alters the path of the jet stream. Put simply, the jet stream in the northern hemisphere delivers storms across the United States. The PDO phase that we appear to have entered will act to steer the jet stream further north over the Western United States.
Q. How does that affect the weather and climate in my area?
A. See the NOAA Climate Prediction Center for weather and climate seasonal outlooks.
Q. If we are entering a different phase, how long will it last?
A. We don't know, but based on past evidence, as shown by scientists Steven Hare and colleagues at the University of Washington, it is likely to last 20-30 years.
Q. What about El Niño and La Niña?
A. These will still continue, they are a pattern that can be thought of as lying on top of the large scale temperature distribution determined by the Pacific Decadal Oscillation.
Q. What is the connection between ocean height as observed by satellites such as Jason-3 and ocean temperature?
A. When the surface layer of the ocean is warmed it expands and hence results in a higher surface.
Q. Will we have a drought in southern California?
A. If the Pacific Decadal Oscillation has switched we are likely to have 20-30 years with lower rainfall that we have had since the late '70's. We will still have winter rains, but the number of really wet years is likely to decrease.
Q. I have heard that some scientists do not agree that the Pacific Decadal Oscillation has switched, what does this mean?
A. Some scientists say it's too soon to tell whether the temperature shift is part of a long-term cycle. Scientists will be studying many types of data and watching to see how temperature patterns across the Pacific ocean evolve over time.
- NASA Sees El Niño Conditions Prevail in the Central Pacific Ocean (NASA)
- Warm Water Creeps into Otherwise-Calm Central Pacific (NASA)
- Muted La Niña Follows Potent El Niño (NASA EO)
- Moody Pacific Unleashes Another Climate Mystery (NASA)
- Pacific Ocean Showing Signs of Major Shifts in the Climate (New York Times)