NOVA Online | Tracking El Niño

The Quiet Revolution
Mapping El Niño
by Mark Hoover

How fast do your eyes glaze over when you read something like this?

"El Niño can be recognized by its heat signature in the equatorial


	Sea surface temperature anomaly, May 25, 1997.

Pacific ocean, typically producing sea surface temperature anomalies of three to five degrees C in the tropical surface layer east of 120 W longitude."

But even a five-year old can point to El Niño in this picture; just tell her to look for the red.

A quiet revolution has transformed the study of weather, and many other fields as well. Until the last decade or two, scientists used to pass data around more in tables and lists, and less in pictures. Part of the reason much of science and mathematics has seemed foreboding to lay persons is that it takes practice and specialization to be able to turn words and symbols into pictures, and to then use these mental images to grasp the meaning behind the figures and the technical language. But digital technology is changing that, and fast, by allowing us to collect huge amounts of information in visual form, and to move that data around very quickly.

Picture-based information helps us all be a little more like Einstein, who used visualization as a scalpel to dissect meaning in a geometric way. Einstein Albert Einstein

almost flunked math as a student; his gift was the ability to make a mental movie of the world, and play it in his head while he looked intensely at things other people overlooked. Einstein didn't discover relativity with a paper and pencil; he discovered it by closing his eyes and seeing. He called these visions gedanken, or "thought experiments."

Although our language separates us from other animals, the brain circuitry that creates words and lets us extract meaning from them is relatively new, having arisen only in the last few million years, or perhaps even more recently. In contrast, the circuitry that handles visualization is ancient, with origins hundreds of millions of years in the past. Seeing is a far more powerful way of grasping meaning than listening to or reading descriptive words, simply because we've been doing it for so long. It's our nature.

Unlike words, pictures can be grasped as a whole (psychologists speak of this as "gestalt"), and patterns can be recognized instantly. Many scientists talk People in an art gallery looking at the artwork

People in an art gallery looking at the artwork

about seeing a pattern "rise up" out of a picture. Face recognition is a good example of the brain's visual circuits in action. Even the best police sketch artists must spend hours with witnesses trying to convert words back into a visual image of a suspect. There is a gulf between the verbal and visual realms.

To understand El Niño requires finding its patterns, and for that there's nothing better than a map. For an example of how fast science is


Comparison of four recent El Niños—1982, 1991, 1994, and 1997. Full-size animation (700k)

changing, and how much better the tools and maps are for finding patterns are getting, look at this panel. It compares four recent El Niños—1982, 1991, 1994, and 1997—by showing the abnormalities in ocean temperature they produced. Run the animation, and in less than thirty seconds you should be able to rank each of these El Niños by intensity. You are (probably) doing this on your own computer, and you (probably) do not have a degree in weather science. Times are changing when so many of us have such power at hand.

Imagine trying to do what Gilbert Walker did in the early part of this century, when he was looking for the patterns that underlie El Niño. He collected a stockpile of written weather records from a number of locations

This panel maps the El Niño signal in animations of surface data from three satellite instruments: at the top is wind speed from NSCAT, in the middle is sea surface height from TOPEX/Poseidon, and on the bottom is temperature from AVHRR. The ability to see at a glance if a pattern of interaction exists between the three maps is just as important as the data itself. May 1, 1997 is shown. Full size still from animation (130k) | Animation: QuickTime (9MB) | AVI (9MB) | MPEG (2.1MB) | Get QuickTime Software

around the Pacific and India, and started looking for patterns in the numbers and words, a tough way to find them. It took him years, but he did discover a fundamental pattern of El Niño: he realized that during an El Niño, the east and west sides of the Pacific tended to have mirror image opposite weather.

Now imagine what Walker could have done with some images, like these multi-band comparisons, instead of all those tables of measurements and numbers. He'd have wrapped things up faster than you can say "Nintendo."

Here are some more weather patterns that are easy to see, but would be tedious and clumsy to convey in words. Global wind patterns are particularly difficult to describe verbally, but easy to grasp here in a NASA map drawn from satellite wind measurements.

The idea of a perpetual march of cyclones from west to east across the Temperate Zone is rather tough to describe if you're not in the weather business, although we tried in Global Weather Machine. But it is immediately apparent if you watch this animated combination of radar images


Global wind patterns. Full-size version of image (230k)

(which show rain and clouds) and infrared satellite photos (which show heat) taken over North America. In an image of the South Pole you can see how cyclones travel in a ring at the same latitude, right around the Earth. You'll also quickly see why, because it is constantly swept by cyclones, the US has the world's most violent weather. (In a typical year, 10,000 violent thunderstorms, 1,000 tornadoes and several hurricanes pound the US.) This would be hard to convey without pictures. With the aid of a moving map you have a much clearer idea of how El Niño - which changes the jetstreams that direct the travel of these cyclones—can meddle with weather.

The days of scientists gathering weather information in the field with single instruments, and oceanographers sailing off on a ship for a month of taking readings, have been superceded by satellites and grids of sensors, like the TOGA/TAO buoy array, linked by satellites and networks. A single ocean color


	Composite satellite radar image, June 25, 1994. See animation of June 25-29, 1994 (1.2MB): QuickTime \| AVI

satellite contains nearly two million sample points, and covers nearly two million square kilometers of ocean area. To take as many measurements over the same area from a ship traveling at ten knots would require over a decade. And once the data has been gathered, computers allow the creation of maps—pictures that allow researchers to use the part of the brain best suited to winnowing out hidden patterns and discovering essential truths.

By mapping El Niño, and using computers to sift out the background noise and enhance the foreground patterns, it's possible to begin acquiring a visual understanding of how El Niño works, and how it changes weather around the world.

Photos/Images: (1,6-7) NASA; (2) AIP Niels Bohr Library; (4) NOAA; (5) JPL/NASA.

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