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Advance Warning
by Mark Hoover
In May of 1997, in a game of high stakes, a classic match-up
between computer power and human intuition was about to
unthrone a world champion and reveal the awesome power of
visualization in solving complex "what if?" questions. None of
this, however, had anything to do with Gary Kasparov or
playing chess.
In that month, a leading oceanography journal published an
article about what the champion El Niño computer model
foresaw for the coming year. Unequivocally, the model was
forecasting a cold ocean—the opposite of an El
Niño—throughout the remainder of 1997. For more
than a decade, this model had outperformed all others in
predicting El Niños to come, as well as in predicting
El Niños of the past, if historical data was fed into
it. It was the best of a dozen or more competitors, and now it
was just plain wrong: in May 1997 the fastest-rising and
strongest El Niño ever recorded had already been
brewing for months, and was about to surge across the Pacific
Ocean to wreak havoc in the east.
How could the best model have been so...bad?
Meanwhile, about five months earlier at the Pacific Marine
Environmental Laboratory in Seattle, researchers had noted the
first of a series of pulses in winds above the equatorial
Pacific ocean, pulses that sometimes precede the onset of an
El Niño, and the change immediately caught their
attention. For the first time ever, they were literally
seeing—in real time—a picture of what was
happening on the surface of the ocean and in the air above it,
across the entire basin of the tropical Pacific. They were
using an ingenious new instrument that could tell you in a
glance the current state of the engine of most of Earth's
weather. What they saw was vindicating the visionaries who had
worked 15 years to design and build it. Barely finished two
years earlier, this instrument was letting scientists watch
the birth of
the century's most powerful El
Niño—as it happened.
It is called the Tropical Ocean Global Atmosphere/Tropical
Atmosphere Ocean array, or TOGA/TAO, but most people just call
it the Array. Think of it as climatology's answer to the
Hubble Telescope; with it, scientists are able to see things
in the ocean-atmosphere system that have never been seen
before. And in a sense, it is a telescope, but on a far vaster
scale than even the Hubble.
Like an insect's compound eye, this instrument works by
combining the input from a myriad of sensors into a unified
picture. These sensors are attached to buoys moored on a grid
that stretches across thousands of miles from South America to
Australia, carving the entire region between the Tropic of
Cancer and the Tropic of Capricorn into a checkerboard. In
fact, the picture you see when you use the array is a lot like
a checkerboard, too, where the current state of the ocean and
air are represented by coloring the squares to match the
information the sensors are relaying, via satellite, back to
the lab. This is a checkerboard that pulsates in lockstep with
the ocean and atmosphere itself—a checkerboard that
moves. And now, for the first time since it had been
completed, that checkerboard was moving in ways that suggested
the onset of a powerful El Niño.
Scientists by nature tend to be either measurement oriented,
or theory oriented—observers or thinkers. Computer
models are the products of theory; they try to calculate the
future after being set up, or "initialized," with a static
snapshot of the present. You load them with the best data you
can get and then you push the button.
The Array uses plenty of computers, too, but not in quite the
same way. The Array's computers inhale a flood of measurements
taken minutes before out in the ocean, filter and massage
them, and use them to paint a canvas of present conditions.
The computers also let you play a time series, or animation of
pictures taken previously, like they do on the weather
forecast on the evening news. These animations let you sense a
trend or a pattern without sifting through reams of numbers.
And if El Niño is anything, it is first a pattern, a
rhythm in the dynamics between the sea and the air. Anything
that lets you concentrate on the patterns in El Niño
proves to be very useful indeed.
In short, the Array gave the measurement crowd a sudden leg up
on their more abstract colleagues. Although computer models
have been and will remain a fundamental tool of climate and
weather science, when it came to El Niño, it suddenly
seemed a little circuitous to try to synthesize the future.
Who needed a model when you could simply fire up your personal
computer and see for yourself? Mike McPhaden, a measurement
man, was one of these scientists, and around Christmas of
1996, as he looked at the checkerboard on his screen, he could
see what was coming. He decided to trust his eyes and forget
the model. As it became apparent over the next few months that
a major El Niño was underway, Mike would sometimes feel
amazement...but never surprise.
Compare 1997 with 1982
if you want to see the difference the Array makes. 1982 was
also an extreme El Niño year, and a year in which the
detection systems that existed at that time failed for a
variety of reasons. Ironically, the realization that a huge El
Niño event was underway came at the precise moment an
international convocation of climate scientists was meeting in
Princeton, NJ to discuss El Niño detection. Although
everyone seemed to agree that more detection instruments were
needed, some felt that between traditional land-and sea-based
measurements, and images gotten from the new TIROS satellites,
at least a basic system was in place. Recent advances in El
Niño theory, particularly by Klaus Wyrtki in the
mid-70s, had made the idea of prediction suddenly much more
credible, and some of the world's fastest supercomputers were
in the hands of weather scientists to run the new prediction
models. Further, two NOAA meteorologists, Rassmusson and
Carpenter, had just published a major paper on the so-called
"Canonical El Niño," a detailed composite summary of
three decades worth of Niños from the 1950s, 60s, and
70s. By showing at every phase of development what the ideal
El Niño looked like, this study could serve as a
reference work to compare new events against...kind of like a
bird-watcher's manual for anyone heading out into the field
with binoculars, hoping to spot a crested warbler. You could
simply look it up.
So, in the autumn of 1982, no one in the world was aware of
the impending El Niño and the destruction it would
eventually bring. No one was making any preparations. Sure,
some data retrieved from "ships of opportunity"—ships
that took a few measurements as a courtesy to scientists as
they plied their trade in the Pacific—were showing some
strong temperature readings. A couple of reports from islands
in the Pacific had filtered in, stuff like "lagoon temperature
well above normal today," and so on. But these were so spotty
that it was easy to dismiss the elevated readings as
"outliers," or bad numbers that should be disregarded. After
all, measurements taken by the new satellites weren't showing
anything except normal conditions, definitely not the five or
six degree (Celsius) anomalies the ships had shown. And
according to the new Canonical El Niño reference, none
of the other expected signals were showing up. The models
running on the computers were silent, as well.
By co-incidence, however, the Mexican volcano El Chichon had
recently erupted, and it had pumped millions of tons of
sulfuric acid aerosols into the stratosphere, highly
reflective droplets that acted like a smoke screen to
partially block the vision of the TIROS satellites. The effect
was to lower the apparent sea surface temperatures measured by
the satellites by about five or six degrees, neatly masking
the growing El Niño. No wonder the random ship data
looked weird compared to the neat, complete satellite data
sets.
Further, the El Niño of 1982 developed in ways utterly
unlike the Niños of the previous three decades, surging
and pulsing with unprecedented swiftness, and on
uncharacteristic time scales. In fact, since 1982, no El
Niño has followed the Rassmusson-Carpenter average very
well, which has nothing to do with the quality of Rassmusson's
and Carpenter's work, and a lot to do with the shape-shifting
nature of the ocean-atmosphere dynamics that underlie El
Niño, and possible long-term changes in the cycles upon
which they are based. But in 1982, everyone was thinking the
same way: unless it walked like a duck and quacked like a
duck, it probably wasn't a duck. And no one heard anything in
the ocean that sounded like the quack of El Niño.
Continue: Modelling the interaction of the ocean and the
atmosphere
Photos/Images: (2-4) NOAA; (5) NOAA/ETL in Boulder.
Anatomy of El Niño
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