El Niño is a name for the unusual warming of the ocean's surface, which occurs every 2 to 7 years along the equator in the central and eastern Pacific Ocean. During a strong El Niño, surface temperatures can rise as much as 15°F greater than normal over an immense area, stretching thousands of square miles from the coast of Peru to across the international date line. The addition of this heat and humidity source to the global atmospheric circulation is known to disrupt weather and climate patterns in regions around the world.
During a La Niña, the same region of the Pacific Ocean cools. Though the temperature change is usually not as drastic, La Niña occurs just as frequently as the better-known El Niño.
Neutral is the term used when neither El Niño nor La Niña is present in the Pacific. About half of all years are classified as neutral years.
El Niño and La Niña events tend to repeat roughly every four to seven years, although one is not always followed by the other. The impacts of El Niño and La Niña are highlighted in the U.S. Climate Variations and Southeast Climate Variations sections of this site.
The earth's climate is a dynamic system, with regional variations on many different time scales from seasonal, to year-to-year, up to decades and even longer.
Climate is the long-term (monthly or longer) average or total of weather conditions in a region. Climate is not the same as weather. Weather deals with the short-term movement and development of individual systems (storms, fronts, cyclones, air masses).
On a global scale, the changes in the heat distribution over the surface of the ocean during an El Niño event result in large, far-reaching changes in global climate. These result in many of the impacts highlighted in the U.S. Climate Variations and Southeast Climate Variations sections of the site.
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