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This morning, before writing this column, I spent a considerable
amount of time watering my wilting garden. Meanwhile, the New York
Yankees have been rained out for their third consecutive game. And out
in California? Rain, no rain, rain, no rain... Why are we suffering
such severe weather this summer? In case you have not heard, we are
experiencing a weather phenomenon called El Nino.
What is El Nino, and How Long Will This Last? According to Michael
McPhaden, director of the Tropical Atmosphere Ocean Array, an El Nino
is born when west-blowing Pacific trade winds relax or reverse. Without
the wind at its back, seawater that typically piles up on the jagged
western edge of the Pacific -- around Indonesia, the Philippines and
Australia -- slides back toward the Americas. The sliding water moves
in what scientists call Kelvin waves. "It pushes the cold water down.
That causes the initial warming," said McPhaden. At the same time, the
Pacific reacts to the lost wind by building another series of waves
under water. Called , they roll west toward Indonesia, the Philippines
and Australia. Eventually, the series of waves strikes the coasts of
those countries. Then, it reverses and heads back toward South America,
traveling along the equator. "As it passes," McPhaden said, "it leaves
cold water closer to the surface."
El Nino normally occurs around Christmas and usually last for a few
weeks to a few months. Sometimes an extremely warm event can develop
that last for much longer time periods. A strong El Nino developed in
1991 and lasted until 1995. We are apparently experiencing one of these
stronger El Ninos, as this one has lasted for nearly six months . But
how long will this last? And then what?
The Onset of La Nina After an El Nino event, weather conditions usually
return to normal. However, in some years the trade winds can become
extremely strong and an abnormal accumulation of cold water can occur
in the central and eastern Pacific. This event is called La Nina. Where
El Nino refers to a body of unusually warm water astride the equator by
South America, La Nina describes a sea that's abnormally cool. Two
independent computer models that forecast El Nino see on the horizon a
pronounced cooling of the same area of the Pacific. Sometimes, the cold
water is just enough to return ocean temperatures to normal. Not
always. "Sometimes, it overshoots," McPhaden said. "That would bring a
La Nina after El Nino."
"The models say . . . there will be a cold effect sometime next year --
magnitude and timing to be determined," said Tim Barnett, one of the
model makers at Scripps Institution of Oceanography in La Jolla. The
other model with the La Nina forecast comes from the Center for
Ocean-Land-Atmosphere Studies, a research institute in Calverton, Md.
Climate experts agree that the forecasts should be viewed with
Even without consulting computers, it's a reasonably safe assumption
that the present warm spell will be followed, eventually, by a cold
one. That's because the makings of a La Nina are built in to an El
Nino. As McPhaden puts it, "The seeds for the demise of El Nino are
sown even at its onset." So maybe it's time we stopped blaming El Nino
for all of our maladies. From now on, we can start blaming the onset of
La Nina. Most people will not notice the transition from El Nino to La
Nina, as the weather will still be hot and there will initially be
increased rainfall, particularly in California, which we may from this
point forward refer to as CaliforNina.
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Tropical meteorology, Physical oceanography, Effects of global warming, Oceanography, Climatology, El Nio, La Nia, Nino, Sea surface temperature
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