Near the end of each calendar year, ocean surface temperatures warm along the coasts of Ecuador and northern Peru. In the past, local residents referred to this annual warming as “El Nino,” meaning “The Child,” due to its appearance around the Christmas season. The appearance of El Nino signified the end of the fishing season and the arrival of the time for Peruvian fishermen to repair their nets and maintain their boats.
Every two to seven years a much stronger warming appears along the west coast of South America, which lasts for several months and is often accompanied by heavy rainfall in the arid coastal regions of Ecuador and northern Peru. Over time the term El Niño began to be used in reference to these major warm episodes.
During the 1960s, scientists began to link the abnormally warm waters along the west coast of South America with abnormally warm waters throughout the central and east-central equatorial Pacific. In addition, the warmer than average waters were shown to be closely related to
a global atmospheric pressure oscillation known as the Southern Oscillation.
The term El Niño now refers to the coupled oceanatmosphere
phenomenon characterized by:
- Abnormally warm sea surface temperatures from the date line (180W) east to the South American coast
- Changes in the distribution of tropical rainfall from the eastern Indian Ocean east to the tropical Atlantic
- Changes in sea level pressure throughout the global Tropics (low-index phase of the Southern Oscillation)
- Large-scale atmospheric circulation changes in
the Tropics and portions of the extratropics in both
Other terms commonly used for the El Niño phenomenon include “Pacific warm episode” and “El Niño/ Southern
Oscillation (ENSO) episode.”