Introduction Impacts of the ENSO History of ENSO Research Understanding the Mechanisms of ENSO Atmosphere Oceans Viewing ENSO Numerical Models and ENSO Predicition Teaching and Learning Resouces About This Module

El Niño - Southern Oscillation (ENSO) Learning Module   What is El Niño - Southern Oscillation (ENSO)? El Niño is an excellent example of the interaction between the ocean and the atmosphere and there combined effect on climate. El Niño is a disruption of the ocean-atmosphere system in the tropical Pacific having important consequences for weather around the globe. This condition results in redistribution of rains with flooding and droughts. Along the equator, the western Pacific has some of the world's warmest ocean water, while in the eastern Pacific, cool water wells up, carrying nutrients that support large fish populations. Every two to seven years, strong westward-blowing trade winds subside, and warm water slowly moves back eastward across the Pacific, like water shifting in a giant bathtub. The warm water and shifting winds interrupt the upwelling of cool, nutrient-rich water. Fish die; climatic changes affect many parts of the world. Peruvians named this phenomenon El Niño, for the Christ child, because it first appears around Christmas. El Niño is Spanish for the Chirst Child. Historically, the term was used by the fisherman along the coast Ecuador and Peru to refer to a warm, nutrient-poor, ocean current that typically appears around Christmas-time and last several months. El Nino is accompanied by heavy rains, often resulting in catastrophic flooding. The local economy suffers from the loss of fish and guano birds. El Niño - Southern Oscillation (ENSO) phenomenom is a global event arising from large-scale interaction between the ocean and the atmoshere. The Southern Oscillation, a more recent discovery, refers to an oscillation in the surface pressure (atmospheric mass) between the southeastern tropical Pacific and the Australian-Indonesian regions. When the waters of the eastern Pacific are abnormally warm (an El Niño event) sea level pressure drops in the eastern Pacific and rises in the west. The reduction in the pressure gradient is accompanied by a weakening of the low-latitude easterly trades. Since the late 1950's there have been seven major El Niño events: 1957-58, 1965, 1968-69, 1972-73, 1976-77, 1982-83, 1986-87, 1991-92 and 1994-95. The 1982-83 El Niño was the strongest of this century. The possible interrelationship between El Niño and global weather patterns, especially the simultaneous droughts in the Sovet Union, Africa, Australia, and Central America, was first realized in 1972-73. Relationships between El Nino and other global weather anomalies are known as teleconnections. · USRA/ESSE Learning Modules · This page was last updated 13 June 2000