Weather Information: El Nino

El Nino is an event when the oceanic and atmospheric currents change and trade winds slow and cause ocean temperature warming.

El Niño is a phenomenon that occurs when the ocean and air currents change. The trade winds slow and cause a depression, which leads to an increase in ocean temperature. These changes cause increased rainfall across the southern United States and drier conditions in the west. In normal conditions, the trade winds blow in a westerly direction across the Pacific Ocean, carrying warm water to the west. Colder water rises from below the surface near South America. Rainfall occurs when air rises above the warm water in the west and the east Pacific area is dry.

When the easterly tradewinds become weakened, the colder water doesn't rise as much, so the water surface stays warmer. The rain builds up over the warmer water and therefore drenches the eastern areas, and the western areas stay dry. These changes affect a large area of the atmosphere and cause alterations to the weather patterns due to the changes in the air circulation.

El Niño events can be tracked by taking measurements of the ocean temperatures and testing the strength of the tradewinds. Since the atmosphere and the ocean together create the wind, any changes in either or both of these can be important. There are various theories about what causes El Niño, such as thunderstorm activity that creates strong winds blowing to the east and starting the process of preventing the cooler water to rise.



The term El Niño means Christ Child and was used by South American fishermen when they noticed that the water was warmer than usual around Christmas for several months. The term continues to be used to mean the warming of the waters and the following changes in the weather.

El Niño causes storms in the southern United States to be stronger due to the changes in wind patterns and the warmer than usual waters create a lot more moisture in the atmosphere which then blows toward the southern United States and drops as increased rain. It has been estimated through predictions that El Nino events happen about every two to seven years. The most severe El Niño was in 1982-1983 and caused over $13 billion in damage worldwide. Some countries that were affected were Australia, India, South America, United States, and South Africa. During this even, the tradewinds began blowing in the opposite direction to normal, which caused an even greater shift in the atmospheric and oceanic balance. Droughts and fires occurred in Australia and Indonesia and flooding in South America. The warmer and wetter spring in the eastern United States brought an increase of insects, especially disease-carrying mosquitoes. Animals in the west had to leave the mountain areas to search for food and water as the spring became hotter and drier than normal.

One of the biggest findings about the 1982-1983 El Niño event was that there was a small change to the angular momentum of the earth because of the difference to the tradewinds and jet stream. There is research being done to predict the severity of an El Niño and to forecast the effects of increased rainfall and temperatures, but since this phenomenon is a natural part of the atmospheric and oceanic interactions, there is no way to prevent its occurrence.

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