How is el nino caused

Climate scientists call this kind of re-shuffling internal climate variability. Probably not. The answer depends on many factors, including where you live, how strong the event continues to be, and other climate patterns that develop and influence the seasonal outcome. Scientists have identified a set of typical U. They may happen as often as 80 percent of the time, or as infrequently as 40 percent of the time.

NOAA uses a 5-category alert system for tracking ENSO that is based on a combination of observed conditions, computer model forecasts, and expert scientific judgment. These changes in average conditions must persist for at least five overlapping three-month periods in order to be count as a full-blown episode in the historical record.

The winds near the surface in the tropical Pacific usually blow from east to west. Weak winds allow warm surface waters to build up in the eastern Pacific. Sometimes, but not always, the atmosphere responds to this warming with increased rising air motion and above-average rainfall in the eastern Pacific. As the event develops, the warmed waters cause the winds to weaken even further, which can cause the waters to warm even more. Stronger winds push surface water into the western Pacific.

Meanwhile, cool water from deeper in the ocean rises up in the eastern Pacific. As the event develops, the cooled waters cause the winds to strengthen even further, which can cause the waters to cool even more. They both tend to develop during the spring March-June , reach peak intensity during the late autumn or winter November-February , and then weaken during the spring or early summer March-June.

Better predictions of where and when extreme weather events are likely to happen e. Scientists have high confidence, however, that ENSO itself has been occurring for thousands of years, and will continue into the future. Since a strong jet stream is an important ingredient for severe weather, the position of the jet stream helps to determine the regions more likely to experience tornadoes.

Thus, this region becomes more susceptible to severe weather outbreaks during the winter. Centuries before it was a focus of scientific study, South American fishermen noticed warmer-than-normal coastal Pacific Ocean waters and dramatic decreases in fish catch occurring periodically around Christmas time.

We value your feedback Help us improve our content Your Email Address. Warmer or colder than average ocean temperatures in one part of the world can influence weather around the globe. Watch this Ocean Today video to see how this works.

During normal conditions in the Pacific ocean, trade winds blow west along the equator, taking warm water from South America towards Asia. To replace that warm water, cold water rises from the depths — a process called upwelling. Warm water is pushed back east, toward the west coast of the Americas.

South American fishermen first noticed periods of unusually warm water in the Pacific Ocean in the s. The warmer waters cause the Pacific jet stream to move south of its neutral position.

Normally, strong winds along the equator push the warm surface water near South America westward toward Indonesia. When this happens, the cooler water underneath rises up toward the surface of the ocean near South America.

However, in the fall and winter of some years, these winds are much weaker than usual. They actually blow the other way toward South America instead of Indonesia in October. So the warm surface water along the equator piles up along the coast of South America and then moves north towards California and south toward Chile.