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The El Niño Southern Oscillation is characterized by low ocean surface winds along the Equatorial Pacific, generating warmer than average ocean temperatures.
Animation (Credit: NOAA)
Like a stone tossed in a pond, El Niño’s appearance in the Pacific Ocean has ripple effects that extend around the world.
A natural phenomenon, El Niño (Spanish for “the little boy”) refers to occasional periods of sea surface temperature warming in the tropical Pacific that influence the world’s weather patterns.
El Niño is known for stirring up weather across the globe:
However, unlike concentric rings expanding across a pond’s surface, El Niño’s ripples do not follow a simple pattern. They are highly complex, capable of altering atmospheric features from the surface of the ocean to miles above the Earth.
High resolution (Credit: NOAA)
NOAA scientists are studying El Niño’s effects to better understand not only how El Niño influences our weather, but also to separate natural El Niño fluctuations from human-caused climate change. The array of variables involved — ocean temperature, air temperature, ocean currents, winds at various altitudes, air pressure, to name a few — add to the challenge.
A new study by Melissa Free and Dian Seidel, climate scientists in NOAA’s Air Resources Laboratory in Silver Spring, Md., helps connect some of the pieces in the El Niño puzzle. Their work, published in the December 2009 Journal of Geophysical Research, traces one subset of El Niño ripples from the Pacific Ocean to the stratosphere above the Arctic, and then on to Europe where the phenomenon tends to make winters colder.
Layers of the atmosphere.
High resolution (Credit: NOAA)
Free and Seidel’s work is part of an emerging area of interest for climate and weather researchers investigating how the stratosphere — a layer of the atmosphere beginning about five miles above sea level — influences weather at ground level. The stratospheric layer of the atmosphere is located above the troposphere.
The troposphere begins at the Earth's surface and extends up to 4-12 miles (6-20 km) high. This is where we live. The stratosphere begins above the troposphere and extends up to 31 miles above the Earth's surface. This layer holds 19 percent of the atmosphere's gases but very little water vapor. Scientists are just beginning to learn how conditions in the stratosphere echo downward into the troposphere and affect weather.
Free and Seidel decided to look specifically at El Niño’s ability to influence weather at the ground level by first triggering changes several miles up.
In recent years, scientists have found a connection between another atmospheric feature, swirling upper-level winds called the Arctic vortex, and colder than average winters in Europe. Studying data collected since 1958, Free and Seidel confirmed links between El Niño, the cooling of the tropical stratosphere and the warming of the Arctic stratosphere — three factors that also influence the Arctic vortex.
Scientists have long known about El Niño’s effect on temperatures in the lowest part of the atmosphere, but its effects on the stratosphere have only recently become clearer through studies like this one.
Industries affected by severe weather, droughts or floods — agriculture, cargo shipping and transportation — pay close attention to El Niño. With further study, scientists are confident that we will improve our understanding of El Niño and, ultimately, our ability to prepare for its effects.