El Niño

Description

One can say that El Niño results from an atmospheric disordered state of the circulation of Walker whom one badly manages to explain and who periodically returns . It is large a Running marine of a size comparable with that of the the United States which occurs exceptionally some Année S. It appears on average one or twice by Décennie along the Peruvian coasts at the end of the winter, towards December - January.

In normal weather, a cyclonic zone located in the middle of the Pacifique drives out surface warm water by Vent S of south-east towards the Australia and causes gone up cool water the depths on the coasts of Peru, it is the phenomenon known as upwelling in English.

The first sign of appearance of El Niño is a considerable reinforcement of these winds of south-east. They involve an accumulation of warm water in the Western Pacific, making assemble the sea level on the Australian coasts. But as soon as the winds of the south weaken, “hot” water of the Western Pacific invades those of the Pacific Is. It is then the beginning of the phenomenon. El Niño can thus be connected to a weakening temporary, and very marked, anticyclone present in the middle of the Pacific. The force of the Trade winds of decreasing south-east, one attends a backward flow in mass, towards the American coasts where water is lower, of warm water accumulated in the Western part of the Southern Pacific.

The duration of El Niño is in general of approximately 18 Mois. This time passed, the cool water is propagated towards the west. It is then the end of the phenomenon which can be followed by its reverse Niña . A correlation is remarkable between the atmospheric pressures of the east and the west of the Pacific. When they increase in the west, they decrease in the east, and conversely. This phenomenon accelerates the winds of surface of is in west, of the Peru until in Indonesia or decreases them in period El Niño .

El Niño is still the subject of many research with an aim of discovering the causes of this marine phenomenon.

Study and forecast of the phenomenon

Beginnings of the study of El Niño

; Sir Gilbert Walker and the southern oscillation: British scientist and chief of the Indian weather service, Sir Gilbert Walker was affected in 1920 in India, in order to find a means of envisaging the Asian Mousson. Shining scientific, it was harnessed with the task with determination. It was put in liaison with South American scientists who provided him the result of their studies on the local effects of El Niño. While studying these data climatic S and atmospheric S and that which it had at its disposal, it managed to establish, in 1923, a temporal correlation between the statements barometric S to the west and the east of the southern Pacific. Indeed, it realized that the pressure subsided in the west when it decreased in the east, and conversely. Because of this situation of balance and balance, it named this phenomenon Southern Oscillation ( southern Oscillation in French).

Centering its research on the southern oscillation, Sir Walker succeeds in determining, always in 1923, an index to which it gave his name. This last would have as a function to measure the variation of pressure between the east and the west of the Pacific Ocean. When the index, and thus the variation, increased, the pressure was high in the east of the Pacific, and the Alizé S were stronger. When the index was rather low, the trade winds were less powerful, involving rather soft winters in the Canada and the Western America. The whole is accompanied by drynesses in Australia, Indonesia, India and certain African sectors .

One of his/her colleagues attacked it on this subject in a Scientific magazine, finding “perfectly ridiculous the idea that climatic conditions of so distant areas of the sphere one of the other can be dependant between them kind”. It with what Sir Walker retorted that a more precise explanation was to exist, but that it “would require probably a knowledge of the structures of the wind on levels other than the ground”. That implied concepts and unknown observation aids at the time but the current methods of research actually confirmed the theory of the index of pressure Walker .

; Jacob Bjerknes and phenomenon ENSO: In the decades which followed, the Enquiring S studied the climatic variations considered the enigma of the desert islands of the equatorial central Pacific. These islands, although receiving (according to américano-Canadian climatic statistics) the same quantity of rain that their luxuriant neighbors, were hopelessly sterile. In fact, this sterility was due to a variation of the index of Walker pressure: most of the time, the index of this last was rather high, involving very weak, the even non-existent ones, annual precipitations. However, during one period which repeated both to approximately seven years, these islands mid-June underwent a true flood which lasted several months, of December.

The bond, apparently obvious between this strange phenomenon and El Niño , will however be established only during the Années 1960, by a Norwegian Météorologue : the professor Jacob Bjerknes. It was the first to be noticed, in 1967, the relationship between the observations of Sir Walker and El Niño . The two phenomena agreeing in any point, it had even the idea to supplement the name of El Niño by associating the discovery of the British with it: the phenomenon would name from now on ENSO, that is to say El Niño Southern Oscillation ( El Niño Oscillation southern ).

Professor Bjerknes also established, a few years later, the bond between the changes of Température S on the surface of the Mer, the power of the trade winds and strong the Précipitation S which accompanies usually the barometric Creux S in the east as in the west by the Pacific. What corresponds to the phases of an index of Walker of low index.

A flourishing interest towards the end of the 20th century

Since 1982, date of a ENSO having devastated all the belt of the countries of the intertropical belt and even affected the European climate, of the thousands of Scientific S and researchers of the whole world tried to include/understand the phenomenon. During this period, only two programs brought answers to certain interrogations.

; Program TOGA Launched in 1985, the program of international collaboration Tropical Ocean and Total Atmosphere or TOGA ( Study of the tropical oceans and general study of the atmosphere ), made it possible to better include/understand the coupling ocean-atmosphere, i.e. the relations between one and the other. It lasted 11 years and was used as a basis for launching of its successors. It leant particularly on the variations of the coupling due to El Niño.

; Program WOCE Program launched five years after the TOGA by forty-four country, of which all those of the European Union of the time, the purpose of the World Ocean Circulation Experiment or WOCE ( Expérience on oceanic circulation on a worldwide scale ) was to establish a total oceanic description. It in particular made it possible to establish a climatic model more or less being able to envisage the years lasting which would strike phenomenon ENSO.

; Programs CLIVAR and GODAE The continuation of these programs was taken by CLIVAR , CLI subdues VAR iability and predictability program (Programme of study of forecast and variation of the climate) which studied the climate and the interactions ocean Glace - atmosphere on the scale of planet, and by GODAE , Global Ocean Dated Assimilation Experiment, which, in 2003 - 2005, prepared the installation of a world system of monitoring and climatic forecast.

The years 2000

After stammering beginnings, the study D El Niño known a true rise with the 21e century. The novel methods and the new means placed at the disposal of the researchers made it possible to carry out considerable progresses in the analysis of the phenomenon.
; Research institute for Development (IRD) In 2000, IRD launched program ECOP (climatic Étude of the tropical Pacific Ocean) to study the climatic variations due to ENSO and its opposite, Niña. The same year, the IRD also launched, with a budget of 132.000 €, the program PALEOCEAN which, on its side, studied the corals. Technique of the Coring of the Coral, recently developed, allowed to him to use the corals like paleothermometers. The latter contain Uranium and Strontium, of which the quantity present varies according to the temperature of sea surface, and which one measures by Spectrométrie. These element-witnesses date the corals and attest fluctuation of the sea level during the years. They reveal the presence of Myocardiopathie S, of the living organisms to which the state testifies to the impact of ENSO on the environment.
; A quite particular satellite: In 1992, NASA and CNES were linked to launch the satellite Topex/Poseidon with the rocket ARIANE 4. The machine of 2,4 tons was sent at an altitude of 1.336 km, making a tower of the Ground all the 112 minute S, and being able to observe up to 90% of the oceans. The CNES and NASA reflect the 50 000 daily measurements of Topex/Poseidon at the disposal of the scientific community as of July 1993. More than 600 scientists of 54 countries exploited these measurements, distributed via 2 data banks: one located at the the United States, the other, the center SLOOP, being with Toulouse. This center produced every month a Cédérom gathering all the data collected by the satellite, that is to say nearly 2 million monthly measurements.
In October 2005, an technical incident made lose with the satellite its capacities of operation on orbit, being thus put in impossibility of acquiring new scientific data. The satellite thus finished its mission the January 5th 2006, after 13 years in space and more 60 000 orbits around the Earth.

Forecast

The observations of Topex/Poseidon formed part of several great international scientific programs, among which WOCE, TOGA, CLIVAR, and GODAE (with MERSEA its European component ). The organizations of meteorology, them also, drew from the data of the satellite. Thus, these measurements appeared soon essential, and it became obvious that a new program should take the continuation of Topex/Poseidon.

; The Jason program Since its launching by Delta II the December 7th 2001, the satellite Jason-1, successor of Topex/Poseidon, delivers exploitable data in real-time (approximately 3 hours after the reception of the data). The Jason program was conceived like a series of satellites. Thus the Jason-2 satellite, whose launching is envisaged in 2008, started its phase of development in 2004. The Jason-1 satellite is 5 times lighter than less expensive Topex/Poseidon (only 500 Kilo S for 3 Mètre S of scale) and approximately 2 times. It allows a precision at least equal, if it is not higher, to that of its predecessor, because of collaboration between his measurements and those taken, directly on the oceanic surface of the Earth, by specialized Navire S or weather Balise S.

The altimetric data also provide in almost real time of the oceanic observations allowing the development of weather forecasting. Thanks to measurements of Jason-1, Weather-France thus provides regular bulletins on the state of the ocean but also of the alert in the event of degradation of the weather conditions. Jason-1 forms part of the project of operational Océanographie Mercator, launched in 1997 and become a Grouping of Public interest in 2002 (partnership between the CNES, the CNRS/KNOWLEDGE, IFREMER, the IRD, Weather-France and SHOM). Mercator makes it possible to carry out a monitoring in real-time of the oceans (realization of weekly reports of the state of the sea), but also of the long-term forecasts concerning the bioclimatic phenomena such as El Niño .

Consequences observed

El Niño causes many ic upheavals Climat. The Ocean S and the atmosphere are in continual interaction. The modifications induced on the temperature of surface of the Mer will affect the Vent S.

When the Alizé S blow with their full power, the gone up cool water the depths (upwelling) along the equatorial Pacifique cools the Air which overhangs it, making it too dense so that it rises rather high to allow the vapor water to condense and to form Nuage S and drops of Pluie. Thus the air remains free clouds during the Année S “normals”, and the rain in the equatorial belt is largely confined in the extreme west of the basin, in the vicinity of the Indonesia.

But when the trade winds blow, weaken and regress towards the east during the first stages of an event El Niño , the upwelling slows down and the ocean is heated. The humid air on the surface of the ocean is also heated. It becomes enough light to form thick clouds which produce strong rains along the equator. This modification of the temperatures of oceanic surface is thus responsible for displacement towards the east of the maximum of rain on the central Pacific. The atmospheric adjustments associated correspond to a fall of Pression in the central and Eastern Pacific and to an increase in pressure in the Western Pacific (Indonesia and Australia), favourable with a greater withdrawal of the trade winds.

Thus, the El Niño of 1982 - 1983 produced dramatic effects on the Continent S. In Ecuador and into the north of the Peru approximately 250 cm of Pluie fell during 6 Mois. More towards the west, the anomalies of the Vent diverted the typhoons their roads usual, towards Hawaii or Tahiti not prepared with such weather conditions.

The phenomenon can affect by shock waves the ic conditions Climat in the areas furthest away from the sphere. This message of planetary scales is convoyed by displacements of the areas of tropical rains, which affect then the structures of wind on all planet. The tropical Nuage S carriers of rain deform the air which overhangs them (8 to 16 km above the sea level). The winds which are formed in the air above these clouds will determine the positions of the Mousson S and the roads of the Cyclone S and belts of the intense winds separating the hot and cold areas on the surface from the Ground. During years El Niño , when the zone of rain usually centered on Indonesia moves towards the east, towards the central Pacific, the waves present in the high layers of the atmosphere are affected, causing climatic anomalies on many areas of the sphere.

The impacts of El Niño on the climate with the moderate latitudes are most obvious during the Hiver. For example, the majority of the winters El Niño are soft on the Western and areas of the North-West of the the United States, and rainy Canada on the south of the United States (of the Texas to the Florida). El Niño also affects the climates moderated during the other seasons. But, even during the Winter, El Niño is only one of the many factors which influence the climate of the moderate areas.

Thus, the version 1997 of El Niño caused Sècheresse S and forest fires in Indonesia, strong Pluie S in California and Inondation S in the area of the south-east of the United States. The estimated average temperature of the sphere, on the surface, for the terrestrial and maritime zones, also increased. End of December 1997, a Tempête beating records poured up to 25 cm of Neige in the south-east of the United States. Vaguenesses reaching 4 meters in height broke in the south of San Francisco. Violent generated storms prevailed in Florida, with Tornade S reaching 400 km/h. According to the report/ratio HTTP: /www.unep.org/geo/geo3/french/074.htm#fig23 GEO 3 of UNO, El Niño, have in 1997-98 fact several thousands of died and wounded, and caused damage estimated at 32 to 96 billion dollars.

More recently, in June 2002, a certain effect of El Niño of 2002 was already felt in the tropical areas of South America. Violent rains of Storm S, worst of the eight last Decade S, softened the Chile. Towards the end of the month of December, the Australia underwent worst one century drynesses called it “super-dry”. Fatal storms also broke out on the west coast of the United States. Five days whole of large rains and high winds.

A total phenomenon

In the years 1990 a correlation between the hot period and the planetary climate changes in the short run was highlighted. One of the results obtained is the discovery of the prolongation of El Niño in the tropical areas of the Indian Ocean and the Atlantic Ocean. It was made possible thanks to an analysis of the surface of these Océan S with more than 650.000 measurements taken by Bateau. The sum of data used covers one period of approximately fifteen years. One thus observed, from 12 to 18 Mois after the end of the phenomenon El Niño in the Pacifique, a cyclic warming of the surface of the equatorial Atlantic Ocean. It would seem that it is about a passive answer to the change of Atmospheric pressure and Alizés (pulled by El Niño ) in the area. This reaction of the Atlantic Ocean is not really explained to date, but tends to show the propagation on a worldwide scale consequences of El Niño .

The fact that El Niño from now on is regarded as a total phenomenon, with repercussions in the three principal tropical oceans, should facilitate the explanation of the disturbances of the climate on all the planet. The modifications of the oceanic Température thus can, with the local scales, to modify the absolute Humidité of atmospheric circulation, involving the increase in the pluviometry of the surrounding areas. That makes it possible to give in an intuitive way an idea of the mechanisms which involve the consequences observed especially in the area of the Pacific, but also in a less proportion in the rest of the world. This modification is all the more large, frequent and durable, that the energy of the atmosphere increases, with the temperature, by Greenhouse effect.

El Niño contributes to these anomalies or modifications of the Hygrométrie in a manner that one is not explained well, but which one is almost sure that he is the person in charge and it is in the sense that moisture can be regarded as one of the engines of the atmosphere. All these results are founded on the observation. They are interesting, because they underline the elements which have a great importance, in order to take them into account in the realization of digital simulations, which will in the near future make it possible to include/understand and explain the mechanisms leading to the effects observed on the Climat. The applications of these Recherche S will then make it possible to better prevent the undeniable consequences from now on El Niño on the total climatic system.

External bonds

El Nino, Weather France
El Nino, Futura-sciences
a scientific site of controversy by young engineers (Even ROUAULT and Marianne ESPINASSOUS) about the warming of the climate and the possible bonds with the phenomenon El Niño . Causes? Consequences? El Niño and warming of the climate

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