Articles
El Niño
Reference http://www.africanwater.org/el_nino.htm

What is El Niño?

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 Niño?

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 Niña? 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.

(Picture of The 1997 El Niño observed by TOPEX/Poseidon. The white areas off the tropical coasts of South and North America indicate the pool of warm water.)