University of New Mexico, USA
Biology 576: Landscape Ecology & Macroscopic Dynamics

What is ENSO?

The name El Niño (EN) receives its name from South America where Spanish-speakers noticed a warm current that arrived around the end of the calendar year during Christmas time (El Niño means the Christ-child). The term is now associated with occasionally large warming events, -- times when coastal water warms up excessively and the normal rythm of life in the entire Pacific is disrupted.

The Southern Oscillation (SO) refers to the barometric pressure differential between Darwin, Australia and Tahiti in the South Pacific Ocean. The SO is a see-saw in atmospheric mass between the eastern and western hemispheres. The measured inverse of the oscillation in pressure between Darwin and Tahiti is used to produce the Southern Oscillation Index (SOI).

An ENSO event occurs when the increase in sea surface temperatures (EN) and an extreme Southern Oscillation (pressure high at Darwin and low at Tahiti) occur at the same time. The tropical warmth can displace the jet stream which then steers unusual weather systems into distant regions around the world (from Kerr, R.A., 1992: A successful forecast of an El Niño winter. Science, 255, 403. 24 January, 1992).

La Niña, the counter part to El Niño, presents the opposite conditions of reduced sea surface temperatures, elevated barometric pressure and inhibitied storm formation. Scientists suggest that La Niña events produce drought in the same regions that receive increased rainfall during an El Niño event. For example, when an El Niño event on the coast of Peru and Ecuador brings increased rainfall to North American Southwest, a corresponding La Niña delivers drought to Australia and Indonesia (Kerr, 1988).

The fact that ENSO impacts global weather anomalies around the world is called teleconnection. Teleconnection refers to the links of climate over great distances. Scientists have documented links in distant weather events as a result of an ENSO event. Ropelewski and Halpert (1986) have shown that ENSO events are associated with increased precipitation in southwestern and southeastern United States. In contrast, Kerr has suggested that La Niña events can cause drought in the same regions of North America.

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Other Resources

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• NOAA's latest description of ENSO with great graphic links
• For more information on Teleconnections
• Predicting ENSO
• Effects on Biota
• Planning Applications of ENSO predictions
• Back to Introductory Page on ENSO

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Citations (incomplete)

Kerr, R.A. 1988.

Kerr, R.A. 1992. A Successful Forecast of an El Niño Winter. Science 255, 403.

Ropelewski and Halpert. 1986. North American Precipitation and Temperature Patterns Associated with the El Niño/Southern Oscillation (ENSO). Monthly Weather Review. Vol 114:2352.

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