"Nature Guide Journal"

13 April 2002

It's been showing up in the news of late:  the National Oceanic & Atmospheric Administration (NOAA) predicts another El Niño developing.

Occurring every three to seven years, El Niños are an interruption of the "normal" flow of water and air over the Pacific.

Normally, the prevailing winds drive water at the Pacific equator from east (South America) to west (Indonesia and the Philippines).  The steady winds tend to pile water up at the west end—"sea level" in Indonesia is about a half-meter higher than in Ecuador.  The water warms in the equatorial sun on the long journey, readily evaporating to fuel precipitation in southeast Asia.

Normally, too, prevailing northern winds off the Northwest coast move nearshore surface water south and away from the shore to cause upwelling.  The upwelling essentially fertilizes the sea to fuel a boon in plant and animal life.

During El Niños, the prevailing equatorial winds weaken and the warm water at the equator flows back to the east.  Sea level starts to level out, dropping in the western Pacific and rising in the eastern Pacific, even backing up along the continents toward the poles.

While the trigger for El Niños is debated, the considerable impacts of the event are more widely agreed on.

According to NOAA, as the great mass of sun-warmed water flows back east toward South America, columns of air rising off the warmer water alter the "normal" path of high-altitude air currents.

As the air currents shift, large-scale weather patterns shift with them.  In the Pacific Northwest and the northern US, El Niños usually result in drier, milder winters; the southern US usually experiences wetter winters during an El Niño.  Moderate to severe El Niños typically bring drought to the north and flooding to the south.

The massive movement of warm water and shift in weather patterns apparently causes a domino effect that reaches around the planet.  Altered monsoon patterns in Asia, with resulting drought/floods, have been linked to El Niño.

Here, in the eastern Pacific, the rising warm water and wind change also inhibit summer upwelling while warming the local seas.  The lack of upwelling starves our fisheries; the warm water draws in unusual species.

This regular equatorial switch is known as the "Southern Oscillation."  El Niño/Southern Oscillation (ENSO) is a more complete name, widely used by oceanographers and meteorologists.

Next in the program, watch for the global weather to swing back in the opposite direction:  La Niña.

With improved observations, it's becoming apparent that ENSO is a natural and regularly occurring cycle in the currents of air and water in the Pacific.  A cycle with worldwide impacts significant enough that a prediction of el Niño will always be news.

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Visit our pages on related topics:  

climate

climate effects

upwelling

beach in winter

Or visit NOAA's  El Niño site, or Environment Canada's  El Niño site.

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