A significant increase in sea surface temperature over the eastern and central equatorial Pacific that occurs at irregular intervals, generally ranging between two and seven years. El Niño conditions, which are often characterized by “warm events,” most often develop during the early months of the year and decay during the following year. The term was originally applied by fishermen of northern Peru to a warm annual southward coastal current that develops shortly after the Christmas season; hence the Spanish name referring to “the Christ Child. ” The name subsequently became more commonly used in reference to the occasional very strong coastal warmings that are associated with torrential rains in the desert coastal regions of southern Ecuador– northern Peru. The current definition of El Niño developed following the discovery that the coastal warmings are simply part of a larger-scale phenomenon arising from coupled ocean–atmosphere interactions across a broad expanse of the equatorial Pacific. See also La Niña, Southern Oscillation, ENSO.