Charting El Niño

A June 2001 NASA satellite image shows what may be the beginnings of an El Niño.

SUMMARY:

El Niño, like many weather patterns, is one of those systems that nearly everyone has heard of, but whose origins are not so widely known. An elixir of unusual trade wind patterns and warming waters, the weather event can dominate climatic conditions across the world.

Thank 19th century fishermen for coining the name "El Niño." Fishermen plying the waters off the coast of Peru in the late 1800s were the first to notice an occasional seasonal invasion of warm, southward ocean current that displaced the north-flowing, cold stream in which they normally fished. Typically, it happened around Christmas, or the first of the year -- hence the name "El Niño," which means "little boy" or "Christ child" in Spanish.

Summary Update Key questions

El Niño has been falsely linked to global warming and unfairly blamed for hurricanes in the Atlantic, and properly takes credit for droughts in Australia and floods in California. It also is responsible for regional depletion of fish stocks and fluctuations in seasonal temperatures.

An El Niño occurs when the ocean-atmosphere system in the tropical Pacific Ocean is disrupted. Normally, trade winds blow toward the west across the tropical Pacific Ocean, piling up warm surface water in the west Pacific. In a classic El Niño, the trade winds relax in the central and western Pacific, leaving warm water in the east Pacific. Heavy rainfall follows the warm water eastward, leading to flooding in Peru and California, among other places. Meanwhile, areas far to the west, such as Indonesia and Australia, suffer droughts.

EXTRA INFORMATION Notable effects attributed to El Niño in 1997-98

Displacing heat in the east Pacific also prompts changes in the global atmospheric circulation, meaning changes in weather in regions far removed from the Pacific. The alteration in water temperature also affects fish reproduction, which has repercussions along the aquatic food chain.

El Niños occur about every four years, with the most recent episode occurring in 1997-98. The 1983-84 El Niño is considered the strongest and most devastating on record, responsible for more than 1,000 deaths, causing weather-related disasters on nearly every continent and totaling $10 billion in damages to property and livestock.

El Niño conditions typically last one or two years, and are usually followed by "La Nina," or "little girl," in which a cooling of those same mid-Pacific waters triggers a reversal of climate impacts.

UPDATE:

This week climate researchers at the National Oceanic and Atmospheric Administration (NOAA) cited several consecutive months of abnormally warm ocean temperatures in the mid-Pacific Ocean, and heavy rainfall along South America's Pacific Coast -- both signs that the global weather phenomenon is upon us. "This time around, El Niño will not be as powerful as the 1997-98 event, but we'll track it closely for any change in its projected strength," said NOAA climate specialist Vernon Kousky in a written statement.

El Niño weather conditions tend to emerge about twice a decade, when a convergence of weather conditions prompt water temperatures to rise in the Pacific Ocean along the equator.

In the 1997-98 El Niño, rain and winter storms triggered mudslides on the California coast; unusual snowfall hit the desert Southwest, and a warm, wet winter greeted much of the East and Gulf Coasts.

While the South American impacts have already hit this year -- record rains inundated Santiago Chile two months ago -- the United States often does not see much El Niño impact until winter.

KEY QUESTIONS:

How will El Niño affect the U.S.?

Will it gather strength over the coming months?