Occasionally, the central tropical Pacific Ocean becomes very warm and stays warm for 12 to 18 months. This warm spot slowly flows east until it hits Peru. Then it splits, with a portion flowing north and a portion flowing south.
The air above the unusually warm water heats up and takes in more moisture. As the warm air expands, it changes normal wind currents and alters weather patterns both locally and on a much larger scale. (El Niño can change weather all over the world.)
Scientists call the warm water El Niño, and they call the altered air above it and weather patterns it causes the Southern Oscillation. The entire phenomenon is called the El Niño/Southern Oscillation, or ENSO.
El Niño Effect
Teleconnection patterns are constantly changing. For a number of reasons -- including winds, underwater volcanoes, and deep-sea currents -- the Pacific Ocean changes back and forth from the warm El Niño to the chilly La Niña. When the Pacific Ocean cools, the air above the water becomes cooler as well. The change in ocean temperature affects the air pressure over the water, and the ridges and troughs in the atmosphere (which are caused by high and low air pressure) affect the prevailing winds that, in turn, affect our weather.
La Niña Effect
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