El Nino
What is El Nino?
The oceanic and atmospheric phenomenon known as El Niño occurs in the Pacific Ocean when the western coasts of Ecuador and Peru experience unusually warm ocean conditions that cause climatic disturbances of varying severity. The term is used to describe exceptionally intense and persistent occurrences, although originally it described the warm southerly current that appears in the region every December. These extreme climatic conditions occur every three to seven years and can affect climates around the world for more than a year. The name El Niño, Spanish for "the child," refers to the infant Jesus Christ and is used because the current usually begins during the Christmas season. The phenomenon is know as the El Niño Southern Oscillation, or ENSO, because El Niño is accompanied by a flux in air pressure and wind patterns in the southern Pacific.
What Happens During El Nino?
El Niño causes climatic disturbances when sea surface temperatures in the southeastern tropical Pacific are abnormally high. Usually, the warm waters are restricted to the western tropical Pacific, where temperatures are higher than the eastern waters of coastal Peru and Ecuador by more than 10 degrees Celsius. The air pressure is low over the warmer waters and moist air rises, resulting in the clouds and heavy rainfall typical of southeastern Asia, New Guinea, and northern Australia. In the eastern Pacific, the water is cold and air pressure is high, creating the characteristically arid conditions along coastal South America. In the east cold water rises to the surface as warm surface water is pushed westwards by the trade winds blowing from east to west.
However, during El Niño, the easterly trade winds subside and sometimes change direction. This causes a change in sea surface temperatures and increases in wind and pressure changes. Sea surface temperatures along the western coast of South America experience a substantial increase while the warm water of the western Pacific flows back eastward. As this happens, there is a shift in weather patterns - wet weather conditions normal to the western Pacific move to the east, and the arid conditions common in the east appear in the west.
What Are Its Consequences?
The shift in normal weather conditions can result in heavy rains in South America, and droughts in southern Africa, southeastern Asia and India, as well as unusual weather to parts of North America. El Niño also has economic consequences, for example in coastal Peru and Ecuador many industries and livelihoods are upset by the destruction of fish and bird populations due to a shortage of nutrients in the water.
What is La Nina?
La Niña is characterized by unusually cold ocean temperatures in the Equatorial Pacific, compared to El Niño, which is characterized by unusually warm ocean temperatures in the Equatorial Pacific.
News Services
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El Nino Links
CNN Special on El Nino Articles and links
El Nino Theme Page: Accessing Distributed Information related to El Nino - El Nino related products, including the most recent observational data, forecasts, scientific analyses and historical perspectives.
Index - El Nino Links- includes full text articles online and bibliographies.
SF Bay Area El Nino- from usgs.gov.
IRI El Niño and La Niña Homepage - useful projections.
Tracking El Nino - reports on the effects of El Niño around the world, and what scientists are learning about this mysterious weather phenomenon.
NOAA La Nina Page - information and links on the weather phenomenon characterized by unusually cold ocean temperatures in the Equatorial Pacific.
Frequently Asked Questions About El Nino
1997 El Nino Southern Oscillation - intended to provide near real-time reports primarily on marine and terrestrial events that may be linked to the development of the 1997 El Niño, which appears to be unfolding as one of the most severe in history.
Canadian El Nino Bulletin - facts, forecast, local and global effects.
El Nino and the National Landslide Hazard Outlook for 1997 - 98 - includes maps. From the USGS.