El Niño definition by American Heritage Dictionary
A warming of the ocean surface off the western coast of South America that occurs every 4 to 12 years when upwelling of cold, nutrient-rich water does not occur. It causes die-offs of plankton and fish and affects Pacific jet stream winds, altering storm tracks and creating unusual weather patterns in various parts of the world.
Origin: American Spanish, from Spanish, the Christ child (from its onset being around Christmastide) : el, the (from Latin ille; see al-1 in Indo-European roots) + niño, child (from Old Spanish ninno, from Vulgar Latin *nīnnus).
A warming of the surface water of the eastern and central Pacific Ocean, occurring every four to twelve years when cold water does not rise to the surface, causing unusual weather patterns. The warmer water kills fish and plankton, brings heavy rains to western South America, and causes drought in eastern Australia and Indonesia.
A warming of the surface water of the eastern and central Pacific Ocean, occurring every 4 to 12 years and causing unusual global weather patterns. An El Niño is said to occur when the trade winds that usually push warm surface water westward weaken, allowing the warm water to pool as far eastward as the western coast of South America. When this happens, the typical pattern of coastal upwelling that carries nutrients from the cold depths to the ocean surface is disrupted, and fish and plankton die off in large numbers. El Niño warming is associated with the atmospheric phenomenon known as the southern oscillation , and their combined effect brings heavy rain to western South American and drought to eastern Australia and Indonesia. El Niño also affects the weather in the United States, but not as predictably. Compare La Niña.
top: normal water temperatures, with warm water concentrated in the western tropical Pacific;
bottom: El Niño conditions, with warm water extending from the western tropical Pacific to the eastern Pacific