Glossary · Khoa học Trái Đất
El Niño
The warm phase of the El Niño–Southern Oscillation (ENSO): the ocean surface in the central and eastern tropical Pacific is warmer than average, and the trade winds weaken or sometimes reverse. It can affect weather worldwide.
Under normal conditions, the trade winds blow west along the equator, carrying warm water from South America toward Asia; cold water rises from the depths to replace it. During El Niño, the trade winds weaken and warm water is pushed back east, toward the west coast of the Americas. The opposite phase is La Niña: the winds are stronger than usual, pushing more warm water toward Asia, and upwelling increases off the west coast of the Americas. Between the two is a neutral state. Because ENSO requires changes in both the ocean and the atmosphere, it is a coupled climate phenomenon.
Episodes of El Niño or La Niña typically last nine to twelve months, sometimes years, and occur every two to seven years on average but not on a regular schedule; generally, El Niño occurs more often than La Niña. The name (Spanish for "the boy") comes from South American fishermen, who first noticed periods of unusually warm Pacific water in the 1600s. The full name they used was El Niño de Navidad (Navidad is Christmas), because El Niño typically peaks around December.