E L   N I Ñ O / L A   N I Ñ A


El Niño
    The term El Niño (Spanish for "the little boy" or "the Christ Child") was originally used by fishermen along the coasts of Ecuador and Peru to refer to above-normal sea-surface temperatures that typically appear around Christmas time in the eastern Pacific Ocean and last for several months. But El Niño's effects are not limited to Peru and Ecuador.
    They can impact weather patterns around the world, and the disruption of the normal climate can have profound and even tragic consequences.

How Does El Niño Work?
   In normal years, winds tend to blow from east to west across the waters of the tropical Pacific. The easterly winds (remember that wind directions refer to the direction FROM which the wind comes: an easterly trade wind comes from the EAST and blows WEST) push the surface waters westward across the ocean. In turn, this causes deeper, colder waters to rise to the surface. This "upwelling" of deep ocean waters brings with it nutrients that otherwise would remain near the bottom. Fish populations living in the upper waters are dependent on these nutrients for survival.

   During El Niño years, the winds weaken, reducing or even choking off the upwelling of deep water. The consequent warming of the ocean surface further weakens the winds and strengthens El Niño. As the Pacific continues to heat up, the warmer waters shift eastward, and so do the clouds and thunderstorms that produce heavy rainfall along the equator. This results in changes in jet streams (the winds high aloft), which lead to dry conditions in Indonesia and Australia, and floods in Peru and Ecuador. El Niño events occur on average every 3 to 5 years, though there can be periods of up to a decade without an El Niño.


El Niño's Effects
    The 1982-83 El Niño was unusually strong. In Ecuador and northern Peru, up to 100 inches of rain fell during a six-month period, transforming the coastal desert into grassland dotted with lakes. Abnormal wind patterns also caused the monsoon rains to fall over the central Pacific instead of on the western shores, which led to droughts and disastrous forest fires in Indonesia and Australia. Overall, the loss to the global economy as a result of the El Niño amounted to more than $8 billion.

   Likewise, the winter of 1997-1998 was marked by a record-breaking El Niño event. The result was unusual weather in parts of the world, including the U.S. Severe weather events included flooding in the southeastern United States, major storms in the Northeast, and flooding in California.


[Normal Conditions]
Normal  •  El Niño  •  La Niña

La Niña
   El Niño's twin sister is La Niña ("the little girl" in Spanish). Her effects are, as any siblings would expect, the exact opposite of El Niño's: for instance, precipitation is below normal in California and the southeastern U.S.! La Niña is characterized by below-normal sea surface temperatures in the eastern equatorial Pacific. There are large variations in weather for many U.S. locations from warm spells to cold waves during a La Niña winter.

El Niño and Global Warming: Any Connection?
    Scientists still cannot say with certainty that global warming is affecting El Niño events. In January 1999, however, scientists at the National Center for Atmospheric Research (NCAR) and elsewhere reported that global warming may accentuate El Niño's current and future impacts. El Niño events have become more frequent and have had greater climate impacts over the past century. This change in El Niño events corresponds to a rise in global temperatures. To see how El Niño and La Niña change North America's seasons, check out WHEN.

(Adapted, with permission, from the ERA/NASA/NOAA Climate Change Presentation Kit CD-ROM.) link to RESOURCES

Images provided by NOAA