El Niño / La Niña
Background Information
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What Is El Niño/La Niña?
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El Niño was originally recognized by fisherman off the coast of South America as the appearance of unusually warm water in the equatorial Pacific ocean, occurring near the beginning of the year. El Niño means The Little Boy or Christ child in Spanish. This name was used for the tendency of the phenomenon to arrive around Christmas. La Niña on the other hand means The Little Girl. La Niña is sometimes called El Viejo, anti-El Niño, or simply "a cold event" or "a cold episode". It is characterized by unusually cold ocean temperatures in the equatorial Pacific.
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| El Niño (December 1997) |
La Niña (December 1998) |
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| 1997-98 El Niño Animation |
1998-99 La Niña Animation |
El Niño happens when tropical Pacific Ocean trade winds die out and ocean temperatures become unusually warm. The flip side to El Niño called La Niña, occurs when the trade winds blow unusually hard and the sea temperature become colder than normal. El Niño and La Niña are the warm and cold phases of an oscillation we refer to as El Niño/Southern Oscillation, or ENSO, which has a period of roughly 3-7 years. Although ENSO originates in the tropical Pacific ocean-atmosphere system, it has effects on patterns of weather variability all over the world. It also affects Pacific marine ecosystems and commercially valuable fisheries such as tuna, sardines, salmon, and Peruvian anchovetta. |
| El Niño/La Niña as a physical occurrence is a proven fact. The way it works is a theory (actually several different theories). It is as real as other weather phenomena: thunderstorms, for instance. We recognize its characteristics as similar to previous occurrences, and note that its life cycle is roughly the same each time. (Of course each one is different, as each thunderstorm is different, but the basic evolution is similar enough that we know an El Niño/La Niña when we see it). |
| On the other hand, a difference from thunderstorms is that we have a very good idea what triggers thunderstorms, what conditions make it likely for them to occur, to the point where weather forecast models commonly pinpoint the locations and predicted severity of thunderstorms a day or so in advance. We do not have such knowledge for El Niño/La Niña. Once an El Niño/La Niña has started, we have reasonably good skill in predicting the subsequent evolution over the next 6-9 months, but before it has started we have very little skill in predicting the onset before the event has become obvious. There are a variety of theories for why they start, but none of them has given us real skill in making a forecast in advance, the way we can for thunderstorms. |
| However, there is still plenty of social utility in predicting the evolution of an El Niño after it starts, since that gives 6 months or so warning before the effects come to the US. For instance, a weak to moderate El Niño started earlier this year, and that enables forecasters to predict that the coming winter is likely to be warmer than normal across the northern states, and wetter than normal along the Gulf Coast. |
A much more detailed description of El Niño/Southern Oscillation (ENSO) can be found on the Climate Prediction Center ENSO Cycle page.
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