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Your Worst Fears About El Niño

Posted by feww on March 21, 2010

Worst fears about El Niño may come true

The El Niño, formally known as the El Niño-Southern Oscillation, or “ENSO” for short, is the most significant cause of large-scale climate variability in the tropics. El Niño episodes bring warmer than normal waters to the central and eastern Pacific Ocean from Indonesia in the western end to South America in the eastern end of the  ocean, helping to maintain the above-normal sea surface temperatures.

Figure below shows one of these Kelvin Waves progressing across the Pacific in February 2010.

Kelvin Wave Renews El Niño

The globes show sea surface height anomalies, which means places where the water surface is higher (red) or lower (blue) than average. A higher-than-average sea surface height at a given location indicates that there is a deeper-than-normal layer of warm water. Lower-than-average sea surface height indicates a shallower layer of warm water. The globes are based on 10 days of data centered on January 15, January 30, and February 15.

In January (left-hand globe), sea surface heights across the central and eastern equatorial Pacific were elevated (red), but not extremely so, potentially a sign that El Niño was weakening. But in early February, a strong sea level anomaly appeared northeast of Australia (center globe). This swell of deep, warm water is the start of the Kelvin wave, and by late February, it had spread eastward into the central Pacific (right-hand globe) and re-invigorated the current El Niño.

Where do Kelvin waves come from? Under normal conditions, the tropics’ prevailing easterly winds push Sun-warmed surface waters across the Pacific from the Americas toward Indonesia, creating a deep pool of warm water in the western Pacific. During an El Niño, the trade winds falter, and sometimes even reverse, for months. When the winds that maintain the warm pool falter, a large pulse of warm water from the western Pacific slides back toward the east. NASA Earth Observatory images by Jesse Allen, Kevin Ward, and Robert Simmon. Caption by Rebecca Lindsey, based on interpretation provided by Josh Willis and Bill Patzert, NASA JPL.

Related Links

  • El Niño [Main Page, Links to Weekly Updates Archive]

2 Responses to “Your Worst Fears About El Niño”

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