Chart of ocean surface temperature anomaly [°C] during the last strong El Niño in December 1997

ENSO (El Niño-Southern Oscillation) is a global coupled ocean-atmosphere phenomenon. The Pacific ocean signatures, El Niño and La Niña (also written in English as El Nino and La Nina) are major temperature fluctuations in surface waters of the tropical Eastern Pacific Ocean. The names, from the Spanish for "the little boy" and "the little girl", refer to the Christ child, because the phenomenon is usually noticed around Christmas time in the Pacific Ocean off the west coast of South America. Their effect on climate in the southern hemisphere is profound. These effects were first described in 1923 by Sir Gilbert Thomas Walker from whom the Walker circulation, an important aspect of the Pacific ENSO phenomenon, takes its name. The atmospheric signature, the Southern Oscillation (SO) reflects the monthly or seasonal fluctuations in the air pressure difference between Tahiti and Darwin. Chart of abnormal ocean surface temperatures [ºC] observed in December 1997 during the last strong El Niño (source: National Centers for Environmental Prediction, US). ... Chart of abnormal ocean surface temperatures [ºC] observed in December 1997 during the last strong El Niño (source: National Centers for Environmental Prediction, US). ... The English language is a West Germanic language that originates in England. ... For other meanings of Pacific, see Pacific (disambiguation). ... This page is about the title. ... Christmas (literally, the Mass of Jesus Christ) is a traditional holiday observed on 25 December. ... South America South America is a continent crossed by the equator, with most of its area in the Southern Hemisphere. ... Sir Gilbert Thomas Walker (1868-1958) was an English physicist and statistician of the 20th century. ... The Walker circulation is an atmospheric circulation of air at the equatorial Pacific Ocean, responsible for creating ocean upwelling off the coasts of Peru and Ecuador. ... Map of Tahiti Tahiti is the largest island of French Polynesia. ... Darwin is the territorial capital and most populous city of the Northern Territory. ...

ENSO is a set of interacting parts of a single global system of coupled ocean-atmosphere climate fluctuations that come about as a consequence of oceanic and atmospheric circulation. ENSO is the most prominent known source of inter-annual variability in weather and climate around the world (~3 to 8 years), though not all areas are affected. ENSO has signatures in the Pacific, Atlantic and Indian Oceans. In the Pacific, during major warm events El Niño warming extends over much of the tropical Pacific and becomes clearly linked to the SOI intensity. While ENSO events are basically in phase between the Pacific and Indian Oceans, ENSO events in the Atlantic Ocean lag those in the Pacific by 12-to-18 months. Many of the countries most affected by ENSO events are developing countries within main continents (South America, Africa...), with economies that are largely dependent upon their agricultural and fishery sectors as a major source of food supply, employment, and foreign exchange. New capabilities to predict the onset of ENSO events in the three oceans can have global socio-economical impacts. While ENSO is a global and natural part of the Earth's climate, whether its intensity or frequency may change as a result of global warming is an important concern. Low-frequency variability has been evidenced. Inter-decadal modulation of ENSO might exist. Atmospheric circulation is the large-scale movement of air, and the means (together with the ocean circulation, which is smaller [1]) by which heat is distributed on the surface of the Earth. ...

El Niño and La Niña

El Niño Conditions. Warm water pool approaches South American coast. Absence of cold upwelling increases warming. (NOAA / PMEL / TAO)

Normal Pacific pattern. Equatorial winds gather warm water pool toward west. Cold water upwells along South American coast.

La Niña Conditions. Warm water is further west than usual.

El Niño and La Niña are officially defined as sustained sea surface temperature anomalies of magnitude greater than 0.5°C across the central tropical Pacific Ocean. When the +0.5°C (or -0.5°C) condition is met for a period of less than five months, it is classified as El Niño (or La Niña) conditions. If the anomaly persists for five months or longer, it is classified as an El Niño (or La Niña) episode. In historical times it has occurred at irregular intervals of 2-7 years and has usually lasted one or two years. ENSO/El Niño state. ... ENSO/El Niño state. ... The National Oceanic and Atmospheric Administration (NOAA) is a scientific agency of the United States Department of Commerce focused on the conditions of the oceans and the atmosphere. ... ENSO normal state. ... ENSO normal state. ... ENSO/La Niña state. ... ENSO/La Niña state. ... The historical temperature record shows the fluctuations of the temperature of the atmosphere and the oceans throughout history, and in particular since 1850. ...

The first signs of an El Niño are:

1) Rise in air pressure over the Indian Ocean, Indonesia, and Australia

2) Fall in air pressure over Tahiti and the rest of the central and eastern Pacific Ocean

3) Trade winds in the south Pacific weaken or head east

4) Warm air rises near Peru, causing rain in the deserts there

5) Warm water spreads from the west Pacific to the east Pacific. It takes the rain with it, causing rainfall in normally dry areas.

El Niño's warm current of nutrient-poor tropical water, heated by its eastward passage in the Equatorial Current, replaces the cold, nutrient-rich surface water of the Humboldt Current which support great populations of food fish. In most years the warming lasts only a few weeks or a month, after which the weather patterns return to normal and fishing improves. However, when El Niño conditions last for many months, more extensive ocean warming occurs and its economic impact to local fishing for an international market can be serious. ...

Recent El Niños have occurred in 1986-1987, 1991-1992, 1993, 1994, 1997-1998, and 2002-2003. A rather weak El Niño began in September 2004 and ended in the spring of 2005. Weak La Niña conditions have developed during the past few months, and have been classified as a weak La Niña episode. [1] The El Niño of 1997-1998 was particularly strong and brought the phenomenon to worldwide attention, while the period from 1990-1994 was unusual in that El Niños have rarely occurred in such rapid succession (but were generally weak).

ENSO index

The Walker circulation is seen at the surface as easterly trade winds which move water and air warmed by the sun towards the west. This also creates ocean upwelling off the coasts of Peru and Ecuador and brings nutrient-rich cold water to the surface, increasing fishing stocks. The western side of the equatorial Pacific is characterized by warm, wet low pressure weather as the collected moisture is dumped in the form of typhoons and thunderstorms. The ocean is some 60 cm higher in the eastern Pacific as the result of this motion. Image File history File links Enso_jma. ... Image File history File links Enso_jma. ... The Walker circulation is an atmospheric circulation of air at the equatorial Pacific Ocean, responsible for creating ocean upwelling off the coasts of Peru and Ecuador. ... Upwelling is an oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water towards the ocean surface, replacing the warmer, usually nutrient-deplete surface water. ... For other meanings of Pacific, see Pacific (disambiguation). ...

In the Pacific, La Niña is characterized by unusually cold ocean temperatures in the eastern equatorial Pacific, compared to El Niño, which is characterized by unusually warm ocean temperatures in the same area. Atlantic tropical cyclone activity is generally enhanced during La Niña. The La Niña condition often follows the El Niño, especially when the latter is strong. Strong La Niñas occurred in 1988-1989 and 1998-2001, and weakly in 1995-1996. Cyclone Catarina, a rare South Atlantic tropical cyclone viewed from the International Space Station on March 26, 2004. ...

Regional impacts of warm ENSO episodes (El Niño).

Regional impacts of cold ENSO episodes. (La Niña)

During warm ENSO episodes the normal patterns of tropical precipitation and atmospheric circulation become disrupted. ... During warm ENSO episodes the normal patterns of tropical precipitation and atmospheric circulation become disrupted. ... During cold La Niña episodes the normal patterns of tropical precipitation and atmospheric circulation become disrupted. ... During cold La Niña episodes the normal patterns of tropical precipitation and atmospheric circulation become disrupted. ...

Wider effects of El Niño conditions

Because El Niño's warm pool feeds thunderstorms above, it creates increased rainfall across the east-central and eastern Pacific Ocean.

In South America, the effects of El Niño are direct and stronger than in North America. An El Niño is associated with warm and very wet summers (December-February) along the coasts of northern Peru and Ecuador, causing major flooding whenever the event is strong or extreme. The effects during the months of February, March and April may become critical. Southern Brazil and northern Argentina also experience wetter than normal conditions but mainly during the spring and early summer. Central Chile receives a mild winter with large rainfall, and the Peruvian-Bolivian Altiplano is sometimes exposed to unusual winter snowfall events. Drier and hotter weather occurs in parts of the Amazon River Basin, Colombia and Central America. The Altiplano (Spanish for high plain), where the Andes are at their widest, is the most extensive area of high plateau on earth outside of Tibet. ... The Amazon River (occasionally River Amazon; Spanish: Río Amazonas, Portuguese: Rio Amazonas) of South America is one of the two longest rivers on Earth, the other being the Nile in Africa. ... Map of Central America Central America is an area of the American continent in the Western Hemisphere. ...

Direct effects of El Niño resulting in drier conditions occur in Indonesia, increasing forest fires, in the Philippines, and northern Australia. Drier than normal conditions are also generally observed in Queensland, inland Victoria, inland New South Wales and eastern Tasmania during June-August. Fire in San Bernardino, California Mountains (image taken from the International Space Station) A wildfire, also known as a forest fire, vegetation fire, grass fire, or bushfire (in Australasia), is an uncontrolled fire in wildland often caused by lightning; other common causes are human carelessness and arson. ... Motto: Audax at Fidelis (Bold but Faithful) Nickname: Sunshine State/Smart State Other Australian states and territories Capital Brisbane Government Governor Premier Const. ... Motto: Peace and Prosperity Nickname: Garden State, The Place To Be Other Australian states and territories Capital Melbourne Government Governor Premier Const. ... Motto: Orta Recens Quam Pura Nites (Newly Risen, How Brightly You Shine) Nickname: First State, Premier State Other Australian states and territories Capital Sydney Government Governor Premier Const. ... Motto: Ubertas et Fidelitas (Fertility and Faithfulness) Nickname: The Apple Isle Other Australian states and territories Capital Hobart Government Governor Premier Const. ...

West of the Antarctic Peninsula, the Ross, Bellingshausen, and Amundsen Sea sectors have more sea ice during El Niño. The latter two and the Weddell Sea also become warmer and have higher atmospheric pressure. Antarctic Peninsula map Booth Island and Mount Scott flank the narrow Lemaire Channel on the west side of the Antarctic Peninsula. ... Map of Antarctica (click to enlarge) Ice in the Ross Sea, Antarctica The Ross Sea is a deep bay of the Southern Ocean in Antarctica between Victoria Land and Marie Byrd Land. ... The Bellingshausen Sea (71°00′S 085°00′W) is an area along the west side of the Antarctic Peninsula between Alexander Island and Thurston Island. ... The Amundsen Sea, named for Norwegian polar explorer Roald Amundsen, is an arm of the Southern Ocean off Marie Byrd Land in western Antarctica. ... The Weddell Sea is part of the Southern Ocean. ...

In North America, typically, winters are warmer than normal in the upper Midwest states and Canada, while central and southern California, northwest Mexico and the southeastern U.S., are wetter than normal. Summer is wetter in the intermountain regions of the U.S. The Pacific Northwest states, on the other hand, tend to be drier during an El Niño. During a La Niña, by contrast, the Midwestern U.S. tends to be drier than normal. El Niño is also associated with decreased hurricane activity in the Atlantic. World map showing North America A satellite composite image of North America. ... Official language(s) English Capital Sacramento Largest city Los Angeles Area  - Total  - Width  - Length  - % water  - Latitude  - Longitude Ranked 3rd 410,000 km² 402. ... This article is about weather phenomena. ...

Finally, East Africa, including Kenya, Tanzania and the White Nile basin, experiences in the long rains from March to May wetter than normal conditions. There also are drier than normal conditions from December to February in south-central Africa, mainly in Zambia, Zimbabwe, Mozambique and Botswana. East Africa is a region generally considered to include: Djibouti Eritrea Ethiopia Kenya Somalia Tanzania Uganda Burundi, Rwanda, Madagascar, Malawi, Mozambique, and Sudan are sometimes considered a part of East Africa. ... The White Nile is a river of Africa, one of the two main tributaries of the Nile, the other being the Blue Nile. ...

Non-climate effects

East Pacific fishing

Along the west coast of South America, El Niño reduces the upwelling of cold, nutrient-rich water that sustains large fish populations, which in turn sustain abundant sea birds, whose droppings support the fertilizer industry. Download high resolution version (3591x1539, 711 KB)Fishing gear in the southeast Pacific Ocean from left to right: a Chilean purse seiner; a tuna purse seiner in tropical waters of the equatorial east Pacific; a Peruvian purse seiner; a trawler; and a small purse seiner. ... Download high resolution version (3591x1539, 711 KB)Fishing gear in the southeast Pacific Ocean from left to right: a Chilean purse seiner; a tuna purse seiner in tropical waters of the equatorial east Pacific; a Peruvian purse seiner; a trawler; and a small purse seiner. ... South America South America is a continent crossed by the equator, with most of its area in the Southern Hemisphere. ... Upwelling is an oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water towards the ocean surface, replacing the warmer, usually nutrient-deplete surface water. ... Atlantic herring, Clupea harengus: the most abundant species of fish in the world. ... Fertilizers or fertilisers are compounds given to plants with the intention of promoting growth; they are usually applied either via the soil, for uptake by plant roots, or by foliar spraying, for uptake through leaves. ...

The local fishing industry along the affected coastline can suffer during long-lasting El Niño events. The world's largest fishery collapsed due to overfishing during the 1972 El Niño Peruvian anchoveta reduction. During the 1982-83 event, jack mackerel and anchoveta populations were reduced, scallops increased in warmer water, but hake followed cooler water down the continental slope, while shrimp and sardines moved southward so some catches decreased while others increased. Horse mackerel have increased in the region during warm events. Binomial name Engraulis ringens The Peruvian anchoveta (Engraulis ringens) is a fish of the anchovy family, Engraulidae. ... Mackerel is a common name applied to a number of different species of fish, mostly, but not exclusively, from the family Scombridae. ... Genera See text Scallops are the family Pectinidae of bivalve molluscs. ... The term hake refers to various fish in the families Gadidae (subfamily Phycinae) and Merlucciidae (both subfamilies Merlucciinae and Steindachneriinae). ... Superfamilies and families Alpheoidea Alpheidae - snapping shrimps Barbouriidae Hippolytidae Ogyrididae Atyoidea Atyidae Bresilioidea Agostocarididae Alvinocarididae Bresiliidae Disciadidae Mirocarididae Campylonotoidea Bathypalaemonellidae Campylonotoidae Crangonoidea Crangonidae Glyphocrangonidea Galatheacaridoidea Galatheacarididae Nematocarcinoidea Eugonatonotidae Nematocarcinidae Rhynchocinetidae Xiphocarididae Oplophoroidea Oplophoridae Palaemonoidea Anchistioididae Desmocarididae Euryrhynchidae Gnathophyllidae Hymenoceridae Kakaducarididae Palaemonidae Typhlocarididae Pandaloidea Pandalidae Thalassocarididae Pasiphaeoidea Pasiphaeidae Procaridoidea Procarididae Processoidea... Sardines can refer to: The plural of sardine, a species of fish. ... Mackerel is a common name applied to a number of different species of fish, mostly, but not exclusively, from the family Scombridae. ...

Shifting locations and types of fish due to changing conditions provide challenges for fishing industries. Peruvian sardines have moved during El Niño events to Chilean areas. Other conditions provide further complications, such as the government of Chile in 1991 creating restrictions on the fishing areas for artisanal fishermen and industrial fleets. Sardines or pilchards are a group of several types of small oily fish related to herrings, family Clupeidae. ...

The ENSO variability may contribute to the great success of small fast-growing species along the Peruvian coast, as periods of low population removes predators in the area. Similar effects benefit migratory birds which travel each spring from predator-rich tropical areas to distant winter-stressed nesting areas. There is some evidence that El Nino activity is correlated with incidence of red tides off of the Pacific coast of California. Migration occurs when living things move from one biome to another. ... A red tide off the coast of La Jolla, California. ...

It has been postulated that a strong El Niño led to the demise of the Moche and other pre-Columbian Peruvian cultures. Moche pottery (Image © PROMPERU, used with permission) The Moche civilization (aka the Mochica culture, Early Chimu, Pre-Chimu, Proto-Chimu, etc. ... This is a chart of the Peruvian cultural periods used by archaeologist studying the area. ...

ENSO and global warming

A few years ago, attribution of recent changes (if any) in ENSO or predictions of future changes were very weak [2]. More recent results (e.g. Collins et al.) tend to suggest that the projected tropical warming may follow a somewhat El-Nino like spatial pattern, without necessarily altering the variability about this pattern.

Causes of El Niño

The mechanisms which might cause an El Niño event are still being investigated. It is difficult to find patterns which may show causes or allow forecasts.

Major theories:

• Bjerknes in 1969 suggested that an anomalously warm spot in the eastern Pacific can weaken the east-west temperature difference, causing weakening in the Walker circulation and trade wind flows, which push warm water to the west. The result is increasingly warm water toward the east.
• Wyrtki in 1975 proposed that increased trade winds could build up the western bulge of warm water, and any sudden weakening in the winds would allow that warm water to surge eastward. However, there was no such buildup preceding the 1982-83 event.
• Recharge oscillator: Several mechanisms have been proposed where warmth builds up in the equatorial area, then is dispersed to higher latitudes by an El Niño event. The cooler area then has to "recharge" warmth for several years before another event can take place.
• Western Pacific oscillator: In the western Pacific, several weather conditions can cause easterly wind anomalies. For example, a cyclone to the north and anticyclone to the south force easterly winds between. Such patterns may counteract the westward flows across the Pacific and create a tendency toward continuing the eastward motion. A weakening in the westward currents at such a time may be the final trigger.
• Equatorial Pacific Ocean may tend to be near El Niño conditions, with several random variations affecting behavior. Weather patterns from outside the area or volcanic events may be some such factors.
• The Madden-Julian Oscillation (MJO) is an important source of variability that can contribute to a more rapid evolution toward El Niño conditions through related fluctuations in low-level winds and precipitation over the western and central equatorial Pacific. Eastward-propagating oceanic Kelvin waves can be produced by MJO activity.

The Walker circulation is an atmospheric circulation of air at the equatorial Pacific Ocean, responsible for creating ocean upwelling off the coasts of Peru and Ecuador. ... The Madden-Julian Oscillation (MJO) is an equatorial traveling pattern of anomalous rainfall. ... A Kelvin wave is a wave in the ocean or atmosphere that balances the Earths Coriolis force against a topographic boundary such as a coastline. ...

Southern Oscillation Index (SOI)

SOI index, 1876-2005 on top of ENSO index

Correlation of the SOI against mean sea level pressure

The Southern Oscillation Index (SOI) is calculated from the monthly or seasonal fluctuations in the air pressure difference between Tahiti and Darwin. Image File history File links Enso-soi. ... Image File history File links Enso-soi. ... Image File history File links Soi-map. ... Image File history File links Soi-map. ... Map of Tahiti Tahiti is the largest island of French Polynesia. ... Darwin is the territorial capital and most populous city of the Northern Territory. ...

Sustained negative values of the SOI often indicate El Niño episodes. These negative values are usually accompanied by sustained warming of the central and eastern tropical Pacific Ocean, a decrease in the strength of the Pacific Trade winds, and a reduction in rainfall over eastern and northern Australia. The most recent strong El Niño was in 1997/98. The trade winds are a pattern of wind found in bands around the Earths equatorial region. ...

Positive values of the SOI are associated with stronger Pacific trade winds and warmer sea temperatures to the north of Australia, popularly known as a La Niña episode. Waters in the central and eastern tropical Pacific Ocean become cooler during this time. Together these give an increased probability that eastern and northern Australia will be wetter than normal.

The most recent strong La Niña was in 1988/89; a moderate La Niña event occurred in 1998/99, which weakened back to neutral conditions before reforming for a shorter period in 1999/2000. This last event finished in Autumn 2000.

Western Hemisphere Warm Pool

Study of climate records has found that about half of the summers after an El Niño have unusual warming in the Western Hemisphere Warm Pool (WHWP). This affects weather in the area and seems to be related to the North Atlantic Oscillation. The Western Hemisphere Warm Pool (WHWP) is a region of sea surface temperatures (SST) warmer than 28. ... The North Atlantic oscillation (NAO) is a complex climatic phenomenon in the North Atlantic Ocean (especially associated with fluctuations of climate between Iceland and the Azores). ...

Atlantic effect

An effect similar to El Niño sometimes takes place in the Atlantic Ocean, where water along equatorial Africa's Gulf of Guinea becomes warmer and eastern Brazil becomes cooler and drier. This may be related to El Niño Walker circulation changes over South America. The Gulf of Guinea is the part of the Atlantic southwest of Africa. ...

History

The first mention of the term "El Nino" to refer to climate occurs in 1892, when Captain Camilo Carrilo told the Geographical society congress in Lima that Peruvian sailors named the warm northerly current "El Nino" because it was most noticeable around Christmas. However even before then the phenomenon was of interest because of its effects on biological productivity, with its effects on the guano industry. Also called: La Ciudad de los Reyes (The City of Kings) Founded January 18, 1535 Subdivisions 30 districts Mayor Luis Castañeda Lossio Area 2,664. ... The Chincha guano islands in Peru. ...

Normal conditions along the west Peruvian coast are a cold southerly current (the Peru current) with upwelling water; the upwelling nutrients lead to great oceanic productivity; the cold currents leads to very dry conditions on land. Similar conditions exist elsewhere (California current; Benguela current off south Africa). Thus the replacement of this with warmer northerly water leads to lower biological productivity in the ocean, and more rainfall - often flooding - on land; the connection with flooding was reported in 1895 by Pezet and Eguiguren.

Towards the end of the nineteenth century there was much interest in forecasting climate anomalies (for food production) in India and Australia. Charles Todd, in 1893, suggested that droughts in India and Australia tended to occur at the same time; Norman Lockyer noted the same in 1904. In 1924 Gilbert Walker (after who the Walker circulation is named) first coined the term "Southern Oscillation". Sir Gilbert Thomas Walker (1868-1958) was an English physicist and statistician of the 20th century. ... The Walker circulation is an atmospheric circulation of air at the equatorial Pacific Ocean, responsible for creating ocean upwelling off the coasts of Peru and Ecuador. ...

For most of the twentieth century, El Nino was thought of as a largely local phenomenon.

The major 1982-3 El Nino lead to an upsurge of interest from the scientific community.

Related images

Average equatorial Pacific temperatures. Download high resolution version (432x645, 23 KB)Average Pacific Ocean sea surface temperatures. ...

El Niño effects upon North American weather and atmospheric circulation. Download high resolution version (529x677, 1051 KB)El Niño effects upon North American weather and atmospheric circulation. ...

Map showing Nino3.4 and other index regions Image File history File links Download high resolution version (918x305, 8 KB) Summary Map of various index regions used to measure the strength of an ENSO; plotted over a background of the +2 and +3 oC contours of the 1997-8 DJF surface temperature anomaly. ...

References

• Collins, M., and The CMIP Modelling Groups, 2005: El Niño- or La Niña-like climate change? Clim. Dyn., 24, 89-104. 19

External links

Wikimedia Commons has media related to:

ENSO

• The El Nino Theme Page Explains El Nino and La Nina, provides real time data, forecasts, animations, FAQ, impacts and more.
• NOAA El Nino Page
• The El Nino Story
• ENSO events 1951 - present
• NOAA announces 2004 El Niño
• The Climate of Peru
• Southern Oscillation Index (SOI)
• The WMO announces the detection of the onset of a La Nina event in the Pacific Ocean. (Reuters/YahooNews)

Image File history File links Commons-logo. ... The Wikimedia Commons (also called Commons or Wikicommons) is a repository of free content images, sound and other multimedia files. ... The World Meteorological Organization (WMO) is an intergovernmental organization with a membership of 187 Member States and Territories. ...

Further reading

• César N. Caviedes, 2001. El Niño in History : Storming Through the Ages (University Press of Florida)
• Brian Fagan , 1999. Floods, Famines, and Emperors : El Niño and the Fate of Civilizations (Basic Books)
• Michael H. Glantz, 2001. Currents of change, ISBN 0 521 78672 X