ENSO - What Is El Niņo?
El Niño is a climate phenomenon within the oceanic-atmospheric system in the tropical Pacific Ocean. This occurrence can influence temperature and precipitation patterns not only there but elsewhere in the world.
The name El Niño, in Spanish, means "the child" indicating that the event usually becomes prevalent in December, during the Christmas season. The process that brings El Niño about often occurs several months in advance. Under average conditions the trade winds blow from east to west across the tropical Pacific. This allows warm water to pile up in the western Pacific, while upwelling of colder water occurs in the eastern Pacific.
The net result is a sea surface temperature that is about 8 degrees warmer in the western Pacific. With more evaporation, and more warm air rising, precipitation is enhanced in the western Pacific while the eastern Pacific and parts of South America receive relatively low rainfall totals.
During El Niño, the trade winds relax in the central and eastern Pacific and upwelling of colder water from below is inhibited. Therefore, in the eastern Pacific the water temperature rises. This results in greater precipitation amounts in the eastern Pacific, and sometimes flooding in South American countries such as Peru. However, El Niño also favors drought conditions in Indonesia and Australia.
Several research studies have been done on correlations between El Niño events and seasonal weather conditions. Scientists seem to be finding regular pattern changes, especially in the strongest El Niño years, but every El Niño is different.
Increases in temperature in the central and eastern Pacific result in an increase of evaporation and convection, or thunderstorm activity. This can be observed especially in the winter. This activity energizes the subtropical jet stream which often flows from Southern California, through the Gulf Coast region. Since the general storm track follows the jet stream, rainfall usually increases where the subtropical jet stream flows.
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During El Niņo, the trade winds relax in the central and eastern Pacific and upwelling of colder water from below is inhibited. Therefore, in the eastern Pacific the water temperature rises.
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