Western Regional Climate Center
PROVIDING CLIMATE SERVICES SINCE 1986
El Niño / Southern Oscillation
What is an El Niño?
El Niño is characterized by unusually warm ocean temperatures in the Equatorial Pacific, as opposed to La Niña, which characterized by unusually
cold ocean temperatures in the Equatorial Pacific. El Niño is an oscillation of the ocean-atmosphere system in the tropical Pacific having important
consequences for weather around the globe.
Why does El Niño occur?
El Niño results from interaction between the surface layers of the ocean and the overlying atmosphere in tropical Pacific. It is the internal dynamics of
the coupled ocean-atmosphere system that determine the onset and termination of El Niño events. The physical processes are complicated, but they involve
unstable air-sea interaction and planetary scale oceanic waves. The system oscillates between warm (El Niño) to neutral (or cold) conditions with a natural
periodicity of roughly 3-4 years.
What is ENSO (El Niño/ Southern Oscillation)?
ENSO stands for El Niño/ Southern Oscillation. The ENSO cycle refers to the coherent and sometimes very strong year-to-year variations in sea-surface temperatures,
convective rainfall, surface air pressure, and atmospheric circulation that occur across the equatorial Pacific Ocean. El Niño and La Niña represent opposite
extremes in the ENSO cycle.
El Niño Information
Current And Historical Sea Surface Temperatures
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Western Regional Climate Center