March 5, 2002: Somewhere on a beach in Ecuador or Peru, someone is
out for stroll. A warm breeze is blowing, water laps at their feet.
But something is amiss. The air is a bit warmer than usual. So is the
water. And, for weeks now, tides have been cresting a few inches
higher. Maybe only frequent beach-walkers would notice the
difference, but the changes are real.
These countries have just been hit by a gentle yet massive swell of
warm water -- a so-called "Kelvin wave."
"Kelvin waves are warm bumps in the Pacific Ocean," says JPL
oceanographer Bill Patzert. They form around Indonesia and travel
east toward the Americas. "A typical Kelvin wave is 5 or 10 cm high,
hundreds of kilometers wide, and a few degrees warmer than
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Usually not much happens when a Kelvin wave arrives -- beach combers
experience a bit of extra rain, perhaps, and slightly warmer surf.
Nevertheless, scientists pay careful attention to them because these
gentle waves occasionally herald something far more powerful: the
next El Niño.
Both TAO and TOPEX/Poseidon have tracked the latest Kelvin wave since
it formed near Indonesia in Dec. 2001. "The wave crossed the Pacific
in January and reached South America in February," says Patzert. Not
all Kelvin waves manage to cross the vast Pacific -- but this one
did. It reminds Patzert of another notable Kelvin wave: "It looks a
lot like one that crossed the Pacific in early 1997 -- just before
the last El Niño."
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