Scientists have uncovered evidence of a long-term climate pattern in the North Pacific Ocean. Known as the Pacific Decadal Oscillation (PDO), this long-term ocean fluctuation waxes and wanes roughly every 20 to 30 years, and has been shown to have an important influence on salmon abundance. While the El Nino of the southern Pacific Ocean may appear for a year and then disappear, the PDO tends to run in streaks of 10 to 15 years. This site, from the TOPEX/Poseidon satellite (a cooperative effort of NASA's Jet Propulsion Lab, and Centre National d'Etudes Spatiales) contains satellite data, using "the precise shape of the ocean's surface and how this surface changes through time" to monitor the PDO. Researchers interested in learning more about the Pacific Decadal Oscillation will find this Website to be an excellent base reference.