A moderate "El Nino" event has taken hold in the tropical Pacific, threatening to trigger further weather disruption into the first quarter of 2007, the World Meteorological Organisation said on Friday. Here are some key facts about the weather phenomenon:

WHAT IS EL NINO?
- El Nino refers to the abnormal warming of water in the eastern Pacific Ocean, off the west coast of South America. Normally, trade winds blowing from east to west carry warm water to Indonesia and Australia and allow cooler, nutrient-rich water to rise along the South American coast. El Nino is observed when the easterly trade winds weaken or are reversed, allowing the warmer waters of the western Pacific to move towards the coast of South America.

- El Nino, which means 'little boy' in Spanish, was noticed by Anchovy fishermen in South America in the 19th century. They named it for the Christ child since it appeared around Christmas, and it normally peaked late in the year.

- Scientists do not know for sure how El Nino forms but they can detect its formation and track its progress.

IMPACT
- El Nino usually causes severe droughts and forest fires in Australia, Central America, Indonesia, the Philippines and southern India. It is associated with heavy rain and flooding in Bolivia, Ecuador and the US Gulf States. They also suppress hurricane activity in the Atlantic.

- Marine and bird life can be affected because of the disappearance of the nutrient-rich cold water along the coast of South America.

- The worst El Nino on record in 1997-98 killed over 2,000 people and caused property damage worth an estimated $33 billion.

FREQUENCY
An El Nino usually recurs every 3-7 years with varying degrees of intensity, and conditions are usually felt around the world for over a year. The 1990-94 El Nino period is considered the longest on record.

LA NINA
- La Nina (Little Girl in Spanish), is essentially the opposite of El Nino and refers to times when waters of the eastern Pacific are colder than normal. In areas where El Nino causes flooding, La Nina brings drought and where winter weather was abnormally mild because of El Nino, it turns abnormally harsh due to the effects of La Nina.

- It is not uncommon for an El Nino to be followed by a La Nina. The two phenomenums appear about 30 times every century.
Sources: Reuters; NOAA (www.noaa.gov); NASA (www.nasa.gov); National Geographic (www.nationalgeographic.com)
(Planet Ark, 04/12/2006)
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