How El Nino and La Nina affect U.S. storms
- 10.14.2008
- Article Number: 1
| El Niño and La Niña, the two extremes of the ocean-atmosphere cycle known as the El Niño-Southern Oscillation (ENSO), have a dramatic effect on world weather patterns.
Scientists track the El Niño-Southern Oscillation by watching the temperature of the surface waters of the central and eastern tropical Pacific Ocean. Under normal conditions, easterly trade winds push the warmest surface water of the equatorial Pacific into the western part of the ocean. This westward movement of surface waters allows cold, nutrient-rich water to move from the ocean floor to the surface along the western coast of South America.
During an El Niño event, water temperatures in the central and eastern equatorial Pacific tend to be warmer than normal for an extended period of time — typically at least three to five months. Reduced upwelling can adversely affect local bird and fish populations off the coasts of Ecuador and Peru.
La Niña is sometimes referred to as the "cold phase" of the El Niño-Southern Oscillation, as surface waters in the central and eastern equatorial Pacific tend to be cooler than normal.
Thunderstorms transport heat and moisture from the surface to the upper reaches of the troposphere. The location of thunderstorms across the Pacific basin during El Niño and La Niña events can then influence the west-to-east winds high above the Earth, known as jet streams.
El Niño and La Niña can have noticeable weather impacts in the USA, which vary from season to season. A strong El Niño can result in a stormy winter along the West Coast, a wet winter across the South, and a warmer-than average winter for parts of the North.
During La Niña winters, significant cold-air outbreaks can be more frequent across the northern tier of the USA, while the southern states experience less storminess and precipitation. In the eastern USA, during a La Niñ winter, there are generally fewer coastal storms and more Alberta Clippers than normal.
ALBERTA CLIPPERS: Winter storms that streak across the northern states
In the summer and fall, La Niña can influence hurricane development, often resulting in fewer eastern Pacific hurricanes and more Atlantic hurricanes. El Niño can have the opposite effect, resulting in more eastern Pacific hurricanes and fewer Atlantic hurricanes.
The Climate Prediction Center in Camp Springs, Md., expects that that neither El Niño nor La Niña conditions will dominate through the end of 2008. This "ENSO-neutral pattern" may persist into Spring 2009.
By Bob Swanson and Adrienne Lewis, USA TODAY |
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