El Niño is a climate pattern that describes the unusual warming of surface waters along the tropical west coast of South America. El Nino has an impact on ocean temperatures, the speed and strength of ocean currents, the health of coastal fisheries, and local weather from Australia to South America.
El Niño events occur irregularly at two- to seven-year intervals. However, it is not a regular cycle, or strictly predictable in the sense that ocean tides are.
El Niño has long been recognized by fishers off the coast of Peru as the yearly appearance of unusually warm water in the Pacific Ocean. The name El Niño, meaning the "little boy" in Spanish, was used because the phenomenon often arrived around Christmas.
Peruvian scientists later noted that more intense climatic changes occurred at intervals of several years, shifting the meaning of El Niño to describe these irregular and intense events rather than the annual warming of coastal surface waters.
Led by the work of Sir Gilbert Walker in the 1930s, climatologists determined that El Niño occurs simultaneously with the Southern Oscillation. The Southern Oscillation is a change in atmospheric pressure over the tropical eastern and western Pacific Ocean. When coastal waters become warmer in the eastern tropical Pacific (El Niño), atmospheric pressure decreases in the eastern Pacific and increases in the western Pacific (Southern Oscillation). Climatologists define these linked phenomena as El Nino-Southern Oscillation (ENSO). Today, most scientists use the terms El Niño and ENSO interchangeably.
Scientists use the Oceanic Nino Index (ONI) to measure deviations from normal sea-surface temperatures. El Niño events are indicated by sea-surface temperature increases of more than .5 degrees Celsius (.9 Fahrenheit) for at least five successive three-month seasons. The intensity of El Niño events varies from weak temperature increases about 2-3 degrees Celsius (4-5 degrees Fahrenheit) with only moderate local effects on weather and climate to very strong increases 8-10 degrees Celsius (14-18 degrees Fahrenheit) associated with worldwide climatic changes.
In order to understand the development of El Niño, its important to be familiar with non-El Niño conditions in the Pacific Ocean. Normally, strong trade winds blow west across the tropical Pacific, the region of the Pacific Ocean located between the Tropic of Cancer and the Tropic of Capricorn. These winds push warm surface water toward the west Pacific. The western Pacific Ocean borders Asia, the islands of Oceania, and Australia.
Due to the warm trade winds, the sea surface is normally about .5 meter (1.5 feet) higher and 8 degrees Celsius (14 degrees Fahrenheit) warmer in Indonesia than Ecuador. The westward movement of warmer waters causes cooler waters to rise toward the surface along the coasts of Ecuador, Peru, and Chile. This process is known as upwelling. This cold upwelling elevates the thermocline, the level of ocean depth that separates warm surface water from the colder water below.
Upwelling elevates this cold water, rich in nutrients, to the euphotic zone, the upper layer of the ocean. Nutrients in the cold water include nitrates and phosphates. Tiny organisms called plankton use these nutrients for photosynthesis, the process that creates food from sunlight. Other organisms, such as clams, eat the plankton, while intermediate predators like fish or marine mammals prey on the clams.
Upwelling provides food for a wide variety of marine life, and the tropical South American coastline is home to some of the world's richest fisheries. Some of the fisheries include anchovy, sardine, mackerel, shrimp, tuna, and hake. Fishing is one of the primary industries of Peru, Ecuador, and Chile.
Upwelling also influences global climate. The process increases rainfall over the western Pacific's warmer waters, such as the islands of Indonesia and New Guinea. The eastern Pacific, along...
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