Chances Are (36 page)

These remote stations began to piece together a coherent picture of the living atmosphere, while the new telegraph allowed nearly simultaneous apprehension of the weather over great distances. Starting in 1849, the great hall of the Smithsonian in Washington displayed daily weather charts for the whole republic: a powerful symbol of unity and dominion. Technology also extended exploration into the third dimension. Humboldt had established a new altitude record with his ascent of Chimborazo in 1802, lugging his barometer all the way—but two years later the French physicist Gay-Lussac beat that record in one Paris afternoon, climbing to 23,000 feet in a balloon. He took up a pigeon, a frog, and various insects and brought them back with a flaskful of the upper atmosphere, thus disproving a current theory that at that altitude air was replaced by “noxious fumes.” The courage and single-mindedness of these early observers was astounding. In 1862, the balloonist Coxwell and the meteorologist Glaisher, who published Britain's first daily weather maps, were caught in an updraft that swept them irresistibly to over 30,000 feet. At that height, the pigeons they released dropped like stones in the thin air. They themselves were on the edge of unconsciousness, when, with his last strength, Coxwell managed to pull the gas-valve cord with his teeth. Dramatic stories like this lie behind many lines of data in scientific tables.

 

If, tomorrow, you decide to take your morning walk not around the block or over the hill but straight upward, you will be crossing paths with transcontinental airplanes in about an hour and a half. In that time, you will have traversed the layer that contains almost all the world's active weather: the troposphere. Here is about 80 percent of the atmosphere's mass and almost all its water vapor, packed into a height less than 1 percent of the Earth's radius. This slight gaseous coating is in constant motion, driven by two tireless motors: the Sun's radiation and the Earth's rotation.

Air is heated in the tropics, where more energy arrives from the Sun than can be radiated back into space. This hot air expands, rises, and spreads out from the equator toward the poles. As it does so, it cools and sinks, part returning toward the equator to fill the place of the air now rising there, and part spreading away to form a counter-rotating cell in the higher latitudes. At the same time, though, the Earth is spinning ever eastward; and, like a ball thrown from a moving car, the air masses spreading away from the equator appear to curve with the Earth's rotation as they move toward the poles. Why? Because a point on the equator needs to travel nearly 1,000 miles per hour to complete a turn in one day, whereas a point, say, a hand's breadth from the North Pole need travel only an inch per hour. These two forces, the vertical heat cycle and the horizontal curl of inertia, combine to form the swirling patterns familiar from satellite pictures.

If this were all, weather everywhere would be predictable—even boring. But many other forces are at work: the changing seasons; the varying friction of air moving over land and sea; the exchange of energy through evaporation and condensation, the thermal transport of ocean currents, the reflection of snow, the insulation of clouds—and the influence of life itself, breathing, belching, and burning.

This complexity gives weather the puzzling variety of nature as a whole, and it stimulates what might be called the bird-watching instinct in humans: a willingness to observe and record things for which we have no clear explanation. The first surviving methodical weather diary dates from the 1330s and, almost inevitably, was kept by an English country clergyman: William Merle, Rector of Driby. How much the natural sciences owe to the English habit of confining university-educated men to what Sydney Smith called the “healthy grave” of a country parish! Big minds concentrated in little worlds, they were scholars enough to know that knowledge grows from accurate, repeated observation. Their efforts gave Britain an unequaled resource: weather diaries for much of the country in a continuous series from about 1650.

The most famous in this tradition of clergyman-naturalists (trained in Divinity, although he never actually took orders) was Charles Darwin. It was both these qualifications that brought him to the attention of Captain Fitzroy, leader of the
Beagle
's voyage of exploration in 1831. Fitzroy was an unpredictable character—pious and impatient, philanthropic and quarrelsome—and was passionately devoted to the barometer as an instrument of revelation.

After nearly five years confined together in a space scarcely ninety feet long, the two men separated to write their individual accounts of their voyage. Darwin's is the accomplishment known throughout the world and for all time; Fitzroy's meteorological charts and notes, although produced with equal care and precision, were faintly praised as “all that is immediately wanted.” Darwin's reasoning was a rhythm of induction, hypothesis, and deduction: he saw pattern, inferred cause, and proposed tests. His work was successful (and provocative) because it was convincing
as an idea,
inviting further realization. Contemporary weather science, though, lacked that intellectual foundation: its aim was to predict, but its only means was to describe. If subsequent mariners found the winds off Valparaiso ten points west of Fitzroy's estimate, the whole of his work would be useless—and it would all be his fault.

The need to predict storms, in particular, exercised the British Admiralty. The terrible Crimean winter of 1854, the one that filled Florence Nightingale's hospitals, was made all the worse for the wretched soldiers and sailors by the Black Sea tempest of November 14, which sank the ships bringing their tents, their blankets, and their winter clothes. It was a storm that had made its destructive way across Europe for two days, yet no one in the Crimea had news of it. This harsh lesson prompted France and Britain to consider telegraphic early-warning systems along the known storm tracks. Following the recommendations of an international meeting chaired by Quetelet, the British government set up a Meteorological Office with Fitzroy in charge.

Thousands of sailors' descendants owe their existence to Fitzroy. Britain's coasts see a great variety of filthy weather, made more intense by the shallowness of the surrounding waters. Fitzroy's storm warnings were the direct ancestor of the Shipping Forecast, the midnight radio litany that briefly carries British listeners out of their warm beds into the salt-scented, pitching dark: “Biscay, Fitzroy, Sole: southwest gale 8; thundery showers. Moderate or poor.”

Fitzroy drove his assistants hard and himself yet harder, producing a 24-hour predictive map for the British Isles—the first attempted snapshot of future weather. From 1862 on, the Meteorological Office was able to issue a daily forecast, published in the
Times
. But if Fitzroy was expecting the thanks of a grateful nation, he was to be disappointed. The
Times
, taking his predictions with one hand, slapped him down with the other: “Whatever may be the progress of the sciences, never will observers who are trustworthy and careful of their reputations venture to foretell the state of the weather.” And when Fitzroy published the summary of his lifetime's experience,
The Weather Book,
he had the misfortune to be reviewed by Francis Galton: “Surely, a collection of facts made by a couple of clerks working for a few weeks would set this simple question, and many others like it, at rest.”
Surely?
A
couple of clerks,
when Fitzroy's staff was working eleven hours a day, six days a week? A
simple question,
when it had absorbed the attention of a lifetime? But observation, however diligent, is not the same as understanding the forces that generate phonomena. Fitzroy had collected valuable weather-wisdom, but weather-wisdom is not science—and that is what would be needed for weather forecasting.

 

Those who look down can see wonders as well as those who look up. The French mathematician Jean Leray did much of his research leaning over the rail of the Pont Neuf and staring at the Seine as it swirled past the bridge piers. Turbulence has fascinated scientists and mathematicians from Leonardo to Kolmogorov, and artists from the illuminators of the Book of Kells to the devisers of Maori tattoos. The fascination is its orderly disorder: within a well-defined, closed system (like the Seine) things happen that defy prediction. An eddy switches from left to right of the third pier; a whorl generates two, then three, dependent counter-whorls. While the stars sing of eternal structure, turbulence trills the uncertainty at the heart of life.

Nineteenth-century science kept coming up against turbulence as it attempted to capture the motion of great masses of indistinguishable particles, from steam molecules to electrons. The Norwegian Vilhelm Bjerknes worked on this swirling frontier of physics, studying the formation of vortices in incompressible fluids. He saw how the discipline was shifting toward a collective analysis of movement and energy, describing not the position of individual particles but the state of a system.

In 1898 Bjerknes made a crucial connection that shows it is indeed better to have colleagues than to work in isolation. He was reading a paper that described how vortices formed in a compressible fluid, such as air. It seemed that this could occur only where the gradients of pressure were not the same as the gradients of density: such as when heat increases local fluid pressure without increasing local density. Bjerknes had a friend, Nils Ekholm, who worked in the Swedish weather service and who had just discovered that pressure and density gradients do not coincide
in the atmosphere
. Bjerknes saw the application immediately: whenever air moves from high pressure to low across a skew density gradient, vertically or horizontally—whether in an onshore breeze, in a tornado, or going up a chimney—it will be given a rotation that can be calculated precisely. Turbulent weather was not inherently incomprehensible: it was simply a very large problem in fluid dynamics.

Bjerknes followed up his work with a paper in 1904 that set out the four simple equations for describing atmospheric movement as a problem in pure mathematics, combining Newton's laws of motion with the first two laws of thermodynamics. Here were hope and horror in equal proportions. The weather was at last reduced to a closed set of predictive equations for an easily defined system: a compressible fluid with friction (and, in thermodynamic terms, an ideal gas). But these equations, when applied to a geographically fixed frame of reference, can be non-linear. That is, they contain terms that do not vary directly with one another; some, indeed, are determined by each other in a circular fashion: friction, for instance, depends on velocity but also
affects
velocity. Groups of simultaneous linear equations can be solved; non-linear ones often cannot. So while Bjerknes offered a license to predict weather indefinitely into the future, this license did not apply on our planet.

Bjerknes might have been content to leave things at this impasse, but history intervened. He was working in Leipzig in 1917; the German military was beginning to realize the importance of accurate weather forecasting to its war effort, which put Bjerknes, as a neutral citizen, in an increasingly difficult position. His mother pulled some strings and got him invited back to Norway to run an as yet nonexistent geophysical institute in Bergen, an ideal place to study weather: it rains there two days out of three—you can even buy umbrellas from vending machines on its streets.

Bergen shipowners financed the institute to solve one pressing problem: Norway traditionally relied for its storm warnings on the British Meteorological Office—but now, in danger from Zeppelin raiders, the British considered North Atlantic weather to be a military secret. Without accurate forecasts, the Norwegian herring fleet risked catastrophe every time it ventured out into the tempestuous basin of the North Sea. Bjerknes set up a network of local observers up and down the coast to gather and send in enough precise and consistent data to make up for the missing Atlantic reports, giving him at least a chance of using his equations to make useful predictions.

Thanks to these detailed synchronous observations, the Bergen group came out of the war with a new understanding of how storms are generated: not simply in areas of low pressure, but along the local intersection planes of contrasting air masses. Influenced by the current language of battle, they called these “fronts,” and showed how these fronts waver and bend, folding back on themselves and spawning circular squalls. The Bergen group invented the map—with its snaking lines, red bumps, blue triangles, and its H and L bullseyes—that we see on every television forecast.

As long as war and economic crisis kept the Norwegian government's attention on meteorology, Bjerknes had the funds and the authority to gather the data he needed. With the Armistice, though, Bjerknes was driven back onto weather lore: his remaining observers were asked to report on the look of the sky, to report “dark air” or “brewing up” as a sign of trouble to come. The man who had promised that meteorology could be considered purely as a problem in mathematics was forced to trudge in the footsteps of Aratus.

 

The two great problems of meteorology remain data collection and interpretation. Bjerknes had opened up the prospect of deterministic forecasts, if only there was enough information to feed into his equations. Accurate prediction seemed to require Laplace's omniscient observer, who could tell you
all
the future, but only if you could tell him everything about the present. Was there at least a sample on which to try these powerful equations—one moment sufficiently documented to justify wrestling with their nonlinear terms?

There was: May 20, 1910, turned out to be a vital day for the history of weather forecasting. Nothing important happened in the weather itself, but a coordinated set of balloon flights across Europe had brought back a dense, consistent data set describing winds, temperature, and pressure at equal altitudes and times. If it were ever going to be possible to treat the weather purely as a math problem, here was one exercise, at least, that included the answer from the back of the book.