What is ENSO?
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ENSO is an abbreviation for El Nino/Southern Oscillation.
El
Nino is a recurrent and normal oceanolgraphic phenomenon that produces
extreme weather conditions in many parts of the world. El Nino itself is
a testament to the fact that local or regional phenomena can impact distant
places. This surprising result stems from the fact that the oceans and
the atmosphere interact with each other and land through a system of feedback
loops something like a domino effect. Today we are also aware of La
Nina and the largely opposite effects it can create.
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Southern Oscillation was coined by British scientist Sir
Gilbert Walker. During the 1920's, as South American scientists were busy
documenting the local effects of El Nino, Gilbert was in India scanning
meteorological data in hopes of discovering how to predict the severity
of the Asian monsoon. He discovered that barometric pressure readings obtained
from stations on either side of the Pacific fell into a remarkable pattern.
He observed that rising pressure in the east would almost always be accompanied
by falling atmospheric pressure in the west. The reverse held true, as
well. Gilbert described the atmospheric system in the Pacific as a teeter-
totter rocking back and forth. Because the wind's direction and magnitude
are generated in response to pressure differences, extreme swings in either
direction yield El Nino or La Nina years as wind patterns move surface
waters and change the distribution of heat in the equatorial Pacific. The
Southern Oscillation is thus an east-west seesaw of pressures that can
be used to predict the occurrence of El Nino or La Nina. Today, the Southern
Oscillation index is heavily relied upon in forecasting.
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Walker was the first to link such regional observations to
conditions across the globe. He noted that a monsoon season characterized
by "low-index" values often corresponded with drought in Australia, Indonesia,
and portions of Africa. He noted, too, that Western Canadian winters
in "low-index" years were unusually mild. Though chided for linking
such distant events, today we know that El Nino and La Nina spread their
influence around the globe.
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