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El Niño-Southern Oscillation (ENSO) Maintained by IOC  
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‘El Corriente del Niño’, or ‘the little boy's current’ (a periodic warm water current flowing north/south off the Pacific coast of Peru, so called by local fisherman because it brings with it unusually bountiful amounts of dolphinfish, yellowfin tuna, and bonito, and occurs around Christmas time) first made scientific news in 1891, when Peruvian geographers suggested a link between it and anomalously long rainy seasons, to the Lima Geographical Society. Not long after, in 1895, Alfonso Pezet gathered his colleague's information and data and produced a paper titled, 'The Countercurrent El Niño off the coast of Northern Peru.' Later in 1924, Gilbert Walker, in a seemingly unrelated search for a method to predict the Indian monsoons, recognized that changes in pressure zones and precipitation patterns in the Pacific seemed to be linked in a see-saw-like oscillation with changes observed in the Indian Ocean, christened this phenomenon the Southern Oscillation. However, it wasn’t until some forty years later when Jacob Bjerknes of the University of California at Los Angeles proposed a hypothesis based on the interaction of the ocean and the atmosphere that the El Niño current and the Southern Oscillation were recognized as elements of the same natural phenomenon: the El Niño/Southern Oscillation, or ENSO.
ENSO Defined
The El Niño/Southern Oscillation is a disruption of the ocean-atmosphere system that occurs periodically in the tropical Pacific. ENSO oscillates from a warm phase (called the El Niño phase) through a neutral phase (normal conditions) to a cold phase (referred to as La Niña) over a period of 2 – 7 years. The amplitude of the oscillation, i.e. how ‘warm’ and how ‘cold’ the El Niño and La Niña phases get, varies from subtle to extreme. During the neutral phase of ENSO, conditions are ‘normal’ i.e., trade winds blowing westward across the Pacific Ocean pushed by a natural atmospheric pressure difference that is high in the east (Tahiti) and low in the west (Darwin). The warm (El Nino) phase occurs with a reversal of the wind direction and an eastward movement of the warmer waters. The cold (La Nina) phase is the result of the anomalously high westward-blowing winds, which produce strong upwelling and a westward movement of the warmest waters along the equator. The warm (El Niño) phase of an ENSO event has been associated with regional extremes in precipitation. Severe droughts occur in some places (e.g., Indonesia) while torrential rains with flooding occur in others (e.g., Peru). The cold phase of an ENSO event (La Niña) tends to produce the opposite effects in these regions. Sea surface temperatures of El Nino (top graphic) and La Nina (bottom graphic) off the Pacific coast of South America. Graphics courtesy of NOAA
ENSO Impacts
Although ENSO is a disruption in ocean-atmospheric interactions, it has a role in nature: namely it is a mechanism by which Earth distributes and regulates heat, as well as being a stimulant for biodiversity. However, ENSO events also impact fisheries, coral reefs and are associated with increased human vulnerability to certain diseases such as: malaria, dengue and yellow fever, hantavirus, encephalitis, typhoid, hepatitis, dysentery, and cholera. The best way to mitigate the negative impacts on an ENSO event is by being prepared, although forecasting ENSO events is far from an exact science. However researchers are working on increasing the accuracy of prediction models for ENSO events.
All  (6) News   (2) Websites   (3) Documents   (1)
El nino theme page, with access to various sources of information on the phenomenum El Nino Home Page of NOAA / Pacific Marine Environment Lab El nino theme page, with access to various sources of information on the phenom...  
NOAA website examining the effects of El Nino/ENSO events Impacts of El Nino and Benefits of El Nino Prediction NOAA website examining the effects of El Nino/ENSO events 
Real-time data from moored ocean buoys for improved detection, understanding and prediction of El Niño and La Niña. Tropical Atmosphere Ocean (TAO) Project: Equatorial Pacific (El Nino, La Nina) Real-time data from moored ocean buoys for improved detection, understanding an...  
Brief abstract, with references and diagrams. Indian Ocean Dipole Correlations with Monsoons and ENSO Brief abstract, with references and diagrams. 
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