Average circulation in the south Pacific Ocean

El Niño-Southern Oscillation (ENSO; commonly referred to as simply El Niño) is a global coupled ocean-atmosphere phenomenon. The Pacific ocean signatures, El Niño and La Niña are important temperature fluctuations in surface waters of the tropical Eastern Pacific Ocean. The Pacific Ocean is the largest of the Earth 's Oceanic divisions The name El Niño, from the Spanish for "the little boy", refers to the Christ child, because the phenomenon is usually noticed around Christmas time in the Pacific Ocean off the west coast of South America. The Child Jesus, or Divine Infant, represents the infant Jesus until to the age of twelve South America is a Continent of the Americas, situated entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a ^[1] La Niña, similarly, means "the little girl". 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. Sir Gilbert Thomas Walker, FRS, was a British Physicist and Statistician of the 20th century The Walker circulation (or Walker cell is an idealized air flow which forms on average Zonal Atmospheric circulation of air at the Equator and The atmospheric signature, the Southern Oscillation (SO) reflects the monthly or seasonal fluctuations in the air pressure difference between Tahiti and Darwin, Australia. Tahiti is the largest Island in the Windward group of French Polynesia, located in the Archipelago of Society Islands in the For a topic outline on this subject see List of basic Australia topics. The most recent occurrence of El Niño started in September 2006^[2] and lasted until early 2007. September 2006 was marked by a controversy surrounding statements made by Pope Benedict XVI regarding Islam, during the same week as the fifth anniversary ^[3]. From June 2007 on, data indicated a weak La Niña event, strengthening in early 2008.

ENSO is associated with floods, droughts, and other disturbances in a range of locations around the world. These effects, and the irregularity of the ENSO phenomenon, makes predicting it of high interest. ENSO is the most prominent known source of inter-annual variability in weather and climate around the world (about 3 to 8 years), though not all areas are affected. ENSO has signatures in the Pacific, Atlantic and Indian Oceans.

During major warm events, El Niño warming extends over much of the tropical Pacific and becomes clearly linked to the intensity of the Southern Oscillation. While ENSO effects are basically in phase between the Pacific and Indian Oceans, ENSO effects in the Atlantic Ocean lag behind those in the Pacific by 12 to 18 months. Many of the countries most affected by ENSO are developing countries that are largely dependent upon their agricultural and fishery sectors for food supply, employment, and foreign exchange.

New capabilities to predict the onset of ENSO events can have global socio-economic impacts. While ENSO is a natural part of the Earth's climate, an important concern is whether its intensity or frequency may change as a result of global warming. Global warming is the increase in the average measured temperature of the Low-frequency variability has been evidenced; interdecadal modulation of ENSO from the Pacific Decadal Oscillation (PDO) or the Interdecadal Pacific Oscillation (IPO) might exist. The Pacific Decadal Oscillation (PDO is a pattern of Pacific Climate variability that shifts phases on at least inter-decadal time scale usually about 20 to 30 years The Pacific Decadal Oscillation (PDO is a pattern of Pacific Climate variability that shifts phases on at least inter-decadal time scale usually about 20 to 30 years This could explain the so-called protracted ENSO of the early 1990s.

El Niño and La Niña

Normal Pacific pattern. Equatorial winds gather warm water pool toward west. Cold water upwells along South American coast. (NOAA / PMEL / TAO)

El Niño Conditions. The National Oceanic and Atmospheric Administration ( NOAA) is a scientific agency within the United States Department of Commerce focused on the conditions of the Warm water pool approaches South American coast. Absence of cold upwelling increases warming.

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. Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature The magnitude of a mathematical object is its size a property by which it can be larger or smaller than other objects of the same kind in technical terms an Ordering 5°C across the central tropical Pacific Ocean. When the 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. Historically, it has occurred at irregular intervals of 2-7 years and has usually lasted one or two years.

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 northern Peruvian deserts
5. Warm water spreads from the west Pacific and the Indian Ocean to the east Pacific. Pressure (symbol 'p' is the force per unit Area applied to an object in a direction perpendicular to the surface The trade winds (also called trades) are the prevailing pattern of easterly winds found in the Tropics near the Earth's Equator. It takes the rain with it, causing extensive drought in the western Pacific and rainfall in the normally dry eastern Pacific.

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, also known as the Peru Current, which support great populations of food fish. The Humboldt Current is a cold low- Salinity Ocean current that flows north-westward along the west coast of South America from the southern tip of Chile 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.

During non-El Niño conditions, the Walker circulation is seen at the surface as easterly trade winds which move water and air warmed by the sun towards the west. The Walker circulation (or Walker cell is an idealized air flow which forms on average Zonal Atmospheric circulation of air at the Equator and This also creates ocean upwelling off the coasts of Peru and Ecuador and brings nutrient-rich cold water to the surface, increasing fishing stocks. 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 Peru (Perú Piruw Piruw officially the Republic of Peru ( reˈpuβlika del peˈɾu is a country in western South America. For a topic outline on this subject see List of basic Ecuador topics. 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 Pacific Ocean is the largest of the Earth 's Oceanic divisions A tropical cyclone is a storm system characterized by a low pressure center and numerous Thunderstorms that produce strong winds and Flooding The ocean is some 60 cm higher in the western Pacific as the result of this motion. ^[4][5][6][7]

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. A tropical cyclone is a storm system characterized by a low pressure center and numerous Thunderstorms that produce strong winds and Flooding The La Niña condition often follows the El Niño, especially when the latter is strong.

Regional impacts of warm ENSO episodes (El Niño).

Regional impacts of cold ENSO episodes. (La Niña)

Wider effects of El Niño conditions

See also: Effects of the El Niño-Southern Oscillation in the United States

Because El Niño's warm pool feeds thunderstorms above, it creates increased rainfall across the east-central and eastern Pacific Ocean. This article describes the Effects of ENSO in the United States.

The effects of El Niño in South America 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. Peru (Perú Piruw Piruw officially the Republic of Peru ( reˈpuβlika del peˈɾu is a country in western South America. For a topic outline on this subject see List of basic Ecuador topics. 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. |utc_offset = -2 to -4 |time_zone_DST = BRST |utc_offset_DST = -2 to -5 |cctld For a topic outline on this subject see List of basic Argentina topics. Central Chile receives a mild winter with large rainfall, and the Peruvian-Bolivian Altiplano is sometimes exposed to unusual winter snowfall events. Chile, officially the Republic of Chile ( Spanish:) is a country in South America occupying a long and narrow Coastal strip wedged between the Peru (Perú Piruw Piruw officially the Republic of Peru ( reˈpuβlika del peˈɾu is a country in western South America. The Republic of Bolivia (República de Bolivia) named after Simón Bolívar, is a Landlocked country in central South 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 Drier and hotter weather occurs in parts of the Amazon River Basin, Colombia and Central America. The Amazon River (Rio Amazonas Río Amazonas of South America is the largest river in the world by volume with a total river flow greater than the next top ten largest rivers Colombia (kəˈlʌmbɪə officially the Republic of Colombia () is a country in northwestern South America.

Direct effects of El Niño resulting in drier conditions occur in parts of Southeast Asia and Northern Australia, increasing bush fires and worsening haze and decreasing air quality dramatically. The term northern Australia is generally considered to include the States and territories of Australia of Queensland and the Northern Territory. Ladysmith-RFSJPG|right|thumb| Ladysmith NSW RFS fire fighting tanker]]A Bushfire is a Fire that occurs in the bush (collective term for Haze is traditionally an atmospheric phenomenon where dust smoke and other dry particles obscure the clarity of the sky Drier than normal conditions are also generally observed in Queensland, inland Victoria, inland New South Wales and eastern Tasmania from June to August. Queensland is a state of Australia, occupying the north-eastern corner of the mainland continent Tasmania is an Australian island and state of the same name It is located south of the eastern side of the Continent, being separated from it by Bass

West of the Antarctic Peninsula, the Ross, Bellingshausen, and Amundsen Sea sectors have more sea ice during El Niño. The Antarctic Peninsula is the northernmost part of the mainland of Antarctica, and almost the only part of that continent that extends outside the Antarctic Circle NOAA Ross seajpg|thumb|200px|thumb|Ice in the Ross Sea Antarctica]] The Ross Sea is a deep bay of the Southern Ocean in Antarctica between Victoria The Bellingshausen Sea is an area along the west side of the Antarctic Peninsula, between Alexander Island and Thurston Island. The Amundsen Sea is an arm of the Southern Ocean off Marie Byrd Land in western Antarctica. The latter two and the Weddell Sea also become warmer and have higher atmospheric pressure. The Weddell Sea is part of the Southern Ocean. Its land boundaries are defined by the bay formed from the coasts of Coats Land and the Antarctic Peninsula

In North America, typically, winters are warmer than normal in the upper Midwest states, the Northeast, and Canada, while central and southern California, northwest Mexico and the southwestern U. Country to "Dominion of Canada" or "Canadian Federation" or anything else please read the Talk Page California ( is a US state on the West Coast of the United States, along the Pacific Ocean. The United Mexican States ( or commonly Mexico (ˈmɛksɪkoʊ () is a federal constitutional Republic in North America. S. , are wetter and cooler than normal. Summer is wetter in the intermountain regions of the U. S. The Pacific Northwest states, on the other hand, tend to experience dry but foggy winters and warm, sunny and precocious springs during an El Niño. During a La Niña, by contrast, the Midwestern U. S. tends to be drier than normal. El Niño is associated with increased wave caused coastal erosion along the US Pacific Coast and decreased hurricane activity in the Atlantic, especially south of 25º N; this reduction is largely due to stronger wind sheartropics. A tropical cyclone is a storm system characterized by a low pressure center and numerous Thunderstorms that produce strong winds and Flooding Wind shear, sometimes referred to as windshear or Wind gradient, is a difference in Wind speed and direction over a relatively

Finally, East Africa, including Kenya, Tanzania and the White Nile basin experiences, in the long rains from March to May, wetter than normal conditions. East Africa is the Easternmost Region of the African Continent. The Republic of Kenya is a country in East Africa. It is bordered by Ethiopia to the north Somalia to the northeast Tanzania to the south Tanzania ˌtænzəˈniːə officially the United Republic of Tanzania (Jamhuri ya Muungano wa Tanzania is a country in East Africa bordered by Kenya The White Nile ( Arabic: النيل الأبيض transliterated: an-Nīl al-Ābyadˤ) is a River of Africa, one of the two main There also are drier than normal conditions from December to February in south-central Africa, mainly in Zambia, Zimbabwe, Mozambique and Botswana. The Republic of Zambia (ˈzæmbɪə is a Landlocked country in Southern Africa. See also Great Zimbabwe National Monument. For information about the March and June 2008 presidential elections see Zimbabwean presidential election Mozambique, officially the Republic of Mozambique (Moçambique or República de Moçambique, ʁɛ'publikɐ d musɐ̃'bik is a country in southeastern Africa The Republic of Botswana (Lefatshe la Botswana is a Landlocked nation in Southern Africa.

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). The Western Hemisphere Warm Pool (WHWP is a region of Sea surface temperatures (SST warmer than 28 This affects weather in the area and seems to be related to the North Atlantic Oscillation. The North Atlantic oscillation (NAO is a climatic phenomenon in the North Atlantic Ocean of fluctuations in the difference of Sea-level pressure between

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. The Gulf of Guinea is the part of the Atlantic Ocean southwest of Africa. This is related to El Niño's effect on the Walker circulation over South America, which causes the easterly trade winds in the western Atlantic Ocean region to strengthen.

Cases of double El Niño events have been linked to severe famines related to the extended failure of monsoon rains, as in the book Late Victorian Holocausts. A famine is a widespread shortage of food that may apply to any Faunal species which phenomenon is usually accompanied by regional Malnutrition, Starvation A monsoon is a seasonal prevailing wind which lasts for several months Late Victorian Holocausts El Niño Famines and the Making of the Third World is a Book by Mike Davis concerning the connection between global climate patterns

Non-climate effects

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. South America is a Continent of the Americas, situated entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a 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 Fish are aquatic Vertebrate animals that are typically ectothermic (previously Cold-blooded) covered with scales, and equipped with two Fertilizers ( also spelt fertiliser are chemical compounds given to Plants to promote growth they are usually applied either through the soil for uptake by plant

East Pacific fishing

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. The Peruvian anchoveta ( Engraulis ringens) is a Fish of the Anchovy family Engraulidae. 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. Mackerel is a common name applied to a number of different species of Fish, mostly but not exclusively from the family Scombridae. A scallop (ˈskɒləp or /ˈskæləp/ is a marine Bivalve Mollusk of the family Pectinidae. The term hake refers to Fish in either of family Gadidae (subfamily Phycinae family Merlucciidae (both True shrimp are swimming decapod Crustaceans classified in the Infraorder Caridea, found widely around the world in both fresh For the hide and seek-like game see Hide and seek. Sardines, or pilchards, are a group of several types of small Oily Horse mackerel have increased in the region during warm events. 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. For the hide and seek-like game see Hide and seek. Sardines, or pilchards, are a group of several types of small Oily Chile, officially the Republic of Chile ( Spanish:) is a country in South America occupying a long and narrow Coastal strip wedged between the Other conditions provide further complications, such as the government of Chile in 1991 creating restrictions on the fishing areas for self-employed fishermen and industrial fleets.

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. Bird migration refers to the regular seasonal journeys undertaken by many species of Birds Bird movements include those made in response to changes in food availability There is some evidence that El Niño activity is correlated with incidence of red tides off of the Pacific coast of California. "Red tide" is a common name for a phenomenon known as an Algal bloom, an event in which estuarine marine or fresh water algae accumulate rapidly in the Water

It has been postulated that a strong El Niño led to the demise of the Moche and other pre-Columbian Peruvian cultures. The Moche civilization (alternately the Mochica culture Early Chimu Pre-Chimu Proto-Chimu etc This

A recent study of El Niño patterns suggests that the French Revolution was caused in part by the poor crop yields of 1788-89 in Europe, resulting from an unusually strong El-Niño effect between 1789-93. El Niño-Southern Oscillation ( ENSO; commonly referred to as simply El Niño) is a global coupled ocean-atmosphere phenomenon The French Revolution (1789–1799 was a period of political and social upheaval in the History of France, during which the French governmental structure previously an ^[8]

La Niña

Sea surface skin temperature anomalies in November 2007 showing La Niña conditions

La Niña is the name for the cold phase of ENSO, during which the cold pool in the eastern Pacific intensifies and the trade winds strengthen. The name La Niña originates from Spanish, meaning "the little girl", analogous to El Niño meaning "the little boy". It has also in the past been called anti-El Niño.

Effects of La Niña

Regional impacts of La Niña.

La Niña causes mostly the opposite effects of El Niño, for example, El Niño would cause a wet period in the Midwestern U. S. , while La Niña would typically cause a dry period in this area.

Recent occurrences

There was a strong La Niña episode during 1988-1989. La Niña also formed in 1995, and in 1999-2000. The last La Niña was a minor one, and occurred 2000-2001. Currently, there is a moderate La Niña, which began developing in mid-2007. NOAA confirmed that a moderate La Niña developed in their November El Niño/Southern Oscillation Diagnostic Discussion, and that it will likely continue into 2008. According to NOAA, "Expected La Niña impacts during November – January include a continuation of above-average precipitation over Indonesia and below-average precipitation over the central equatorial Pacific. For the contiguous United States, potential impacts include above average precipitation in the Northern Rockies, Northern California, and in southern and eastern regions of the Pacific Northwest. Below-average precipitation is expected across the southern tier, particularly in the southwestern and southeastern states. "^[9] In March 2008, La Niña caused a drop in sea surface temperatures over Southeast Asia by an amount of 2°C. It also caused heavy rains over Malaysia, Singapore and Indonesia. For the biogeographical region see Malesia Malaysia (məˈleɪʒə or /məˈleɪziə/ is a country that consists of thirteen states and Singapore The Republic of Indonesia ( (Republik Indonesia is a Country in Southeast Asia. "^[10]

ENSO and global warming

A few years ago, attribution of recent changes (if any) in ENSO or predictions of future changes were very weak. ^[11] More recent results^[12] tend to suggest that the projected tropical warming may follow a somewhat El Niño-like spatial pattern, without necessarily altering the variability about this pattern, while the ENSO cycle may be minimally shortened^[13].

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. As the phenomenon is located near the equator, events in both hemispheres may have an effect. As the weather events are somewhat chaotic, the onsets of El Niño-events may also be. This is not to say predicting is totally impossible.

Major theories

• Jacob 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. Jacob Aall Bonnevie Bjerknes ( November 2, 1897, Stockholm Sweden &ndash July 7, 1975, Los Angeles California) was a The Walker circulation (or Walker cell is an idealized air flow which forms on average Zonal Atmospheric circulation of air at the Equator and 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. A relaxation oscillator is an oscillator in which a Capacitor is charged gradually and then discharged rapidly 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 westerly wind anomalies. For example, cyclones north and south of the equator force west-to-east winds between. Such wind may counteract the typical easterly 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 needed to shift into an El Niño.
• 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. A Kelvin wave is a wave in the ocean or atmosphere that balances the Earth's Coriolis force against a topographic boundary such as a coastline The MJO may in turn be influenced by a developing El Niño, leading to a positive feedback^[14]. Positive feedback, sometimes referred to as "cumulative causation" is a Feedback loop system in which the system responds to perturbation in the same direction
• Adams, Mann and Ammann, using statistical analysis of paleoclimatic records, that a volcanic event in the tropics tilts the climate into a state where El Niño-like conditions are favored. (This is caused by the volcano's effect on solar radiation reaching the surface, not by the heat of the eruption itself. )^[15]

History of the theory

The first mention of the term "El Niño" to refer to climate occurs in 1892, when Captain Camilo Carrillo told the Geographical society congress in Lima that Peruvian sailors named the warm northerly current "El Niño" because it was most noticeable around Christmas. Lima is the Capital and largest city of Peru. It is located in the valleys of the Chillón, Rímac and Lurín rivers on a coast overlooking However even before then the phenomenon was of interest because of its effects on biological productivity, with its effects on the guano industry. Guano (from the Quechua 'wanu' via Spanish) is the Feces of Seabirds Bats and seals

Normal conditions along the west Peruvian coast are a cold southerly current (the Humboldt Current) with upwelling water; the upwelling nutrients lead to great oceanic productivity; the cold currents leads to very dry conditions on land. The Humboldt Current is a cold low- Salinity Ocean current that flows north-westward along the west coast of South America from the southern tip of Chile Similar conditions exist elsewhere (California Current; Benguela Current off South Africa; West Australia Current). The California Current is a Pacific Ocean current that moves south along the western coast of North America, beginning off southern British Columbia The frigid waters of the north-flowing Benguela current move from the western coast of South Africa, Namibia and Angola towards north and northwest 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. Charles Todd may refer to Caroline and Charles Todd, American mystery novelists Charles Todd (astronomer (1826–1910 Australian In 1924 Gilbert Walker (for whom the Walker circulation is named) first coined the term "Southern Oscillation". Sir Gilbert Thomas Walker, FRS, was a British Physicist and Statistician of the 20th century The Walker circulation (or Walker cell is an idealized air flow which forms on average Zonal Atmospheric circulation of air at the Equator and

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

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

The 1998 El Niño event caused an estimated 16% of the world’s reef systems to die. Since then, mass coral bleaching has become common worldwide, with all regions having suffered ‘severe bleaching’. ^[16]

History of the phenomenon

ENSO conditions seem to have occurred at every two to seven years for at least the past 300 years, but most of them have been weak.

Major ENSO events have occurred in the years 1790-93, 1828, 1876-78, 1891, 1925-26, 1982-83, and 1997-98. ^[17]

Recent El Niños have occurred in 1986-1987, 1991-1992, 1993, 1994, 1997-1998, 2002-2003, 2004-2005 and 2006-2007.

The El Niño of 1997 - 1998 was particularly strong ^[18] and brought the phenomenon to worldwide attention. The event temporarily warmed air temperature by 3°F, compared to the usual increase of 0. 5°F associated with El Niño events^[19]. The period from 1990-1994 was unusual in that El Niños have rarely occurred in such rapid succession (but were generally weak). There is some debate as to whether global warming increases the intensity and/or frequency of El Niño episodes. Global warming is the increase in the average measured temperature of the (see also the ENSO and Global Warming section above).

Southern Oscillation

The Southern Oscillation is an oscillation in air pressure between the tropical eastern and western Pacific Ocean waters. The Pacific Ocean is the largest of the Earth 's Oceanic divisions The strength of the Southern Oscillation is measured by the Southern Oscillation Index (SOI). The SOI is a record of the monthly or seasonal fluctuations in the normalized surface air pressure difference between Tahiti and Darwin, Australia. Tahiti is the largest Island in the Windward group of French Polynesia, located in the Archipelago of Society Islands in the ^[20].

El Niño episodes, which are associated with negative values of the SOI, 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. Conversely, La Niña episodes are associated with positive values of the SOI and are accompanied by stronger Pacific trade winds and warmer sea temperatures to the north of Australia. Waters in the central and eastern tropical Pacific Ocean become cooler during this time.

Related images

Average equatorial Pacific temperatures.

El Niño effects upon North American weather and atmospheric circulation.

Map showing Nino3. 4 and other index regions

References

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

Data sources

• Values of the Southern Oscillation Index.
• Linear correlation to US climate from the U. S. National Climatic Data Center.

Further reading

• César N. Caviedes, 2001. El Niño in History : Storming Through the Ages (University Press of Florida), ISBN 978-0813020990
• Brian M. Fagan , 1999. Brian Murray Fagan is an author of popular Archaeology books as well as being Emeritus Professor of Anthropology at the University of California Floods, Famines, and Emperors : El Niño and the Fate of Civilizations (Basic Books), ISBN 0-7126-6478-5
• Michael H. Glantz, 2001. Currents of change, ISBN 052178672X
• Mike Davis, 2001. Late Victorian Holocausts: El Niño Famines and the Making of the Third World, ISBN 1859847390
• Kevin E. Trenberth, 1997. Late Victorian Holocausts El Niño Famines and the Making of the Third World is a Book by Mike Davis concerning the connection between global climate patterns Dr Kevin E Trenberth is head of the Climate Analysis Section at the National Center for Atmospheric Research. The definition of El Niño, Bulletin of the American Meteorological Scociety, Vol. 78, No. 12, p. 2771 – 2777. doi:10.1175/1520-0477(1997)078<2771:TDOENO>2.0.CO;2 [3]PDF (130 KB)
• S. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. George Philander, 1990. El Niño, La Niña and the Southern Oscillation (Academic Press Inc. ), ISBN 0125532350

Footnotes

See also

• Indian Ocean Dipole
• La Niña
• Madden-Julian oscillation
• Southern Oscillation
• Pacific Decadal Oscillation

External links

• The El Niño Theme Page Explains El Niño and La Niña, provides real time data, forecasts, animations, FAQ, impacts and more. The Indian Ocean Dipole (IOD is an oceanographic phenomenon affecting climate in the Indian Ocean region El Niño-Southern Oscillation ( ENSO; commonly referred to as simply El Niño) is a global coupled ocean-atmosphere phenomenon El Niño-Southern Oscillation ( ENSO; commonly referred to as simply El Niño) is a global coupled ocean-atmosphere phenomenon The Pacific Decadal Oscillation (PDO is a pattern of Pacific Climate variability that shifts phases on at least inter-decadal time scale usually about 20 to 30 years
• NOAA El Niño Page
• The El Niño Story
• ENSO events 1951 - present
• NOAA announces 2004 El Niño
• El Niño and La Niña from the 1999 International Red Cross World Disasters Report by Eric J. Lyman
• The Climate of Peru
• Southern Oscillation Index (SOI)
• La Niña episodes in the Tropical Pacific
• Information page on El Niño-Southern Oscillation (ENSO)
• List of El Niño and La Niña events since 1950
• Economic Costs of El Niño / La Niña and Economic Benefits from Improved Forecasting from "NOAA Socioeconomics" website initiative