Windswept_ The Story of Wind and Weather - Marq de Villiers [57]
Then various wind directions were simulated, together with the necessary gustiness, and the results plotted on digital video through a technique called stereoscopic particle imaging velocimetry. Because of the gustiness, which in reality is greater for the first few hundred feet of the ball's flight near the ground, no two visualizations were ever quite the same.
Still, the videos clearly illustrated the conflicting information anxious golfers must deal with and confirmed that the anecdotal evidence of wind behavior at Amen Corner is, in fact, largely true. The wind changed significantly along the shot trajectory. Near the twelfth tee, the wind is either directly in the golfer's face or slightly in the direction of the eleventh fairway. But near the peak of the trajectory the wind is moving more closely in the direction of the thirteenth fairway. At the twelfth green is a swirling flow with low wind speeds. If struck in the direction the golfer senses must be right, the ball will travel true for about a third of its path, about fifty yards. Then suddenly it would be hit by a strong crosswind from the left, carrying it depressingly out of plane into the thickets to the right of the fairway. For the last third of its flight these strong cross-winds diminish—they are still there, but weaker. Not one of these directions mirrored the prevailing winds of the day. As a consequence, each shot a golfer makes from the tee will be slightly different because of the natural gustiness. And that very gustiness made accurate prediction almost impossible.
The laboratory had provided detailed evidence that local topography influences wind patterns, and had shown how. A nice byproduct was to provide architects, landscape designers, and farmers with their windbreaks and snow fences with more evidence that careful planting can mitigate wind damage and protect both buildings and crops.
The Augusta National, for its part, could solve the problem of Amen Corner by removing the trees, as they had suspected. But they had no intention of doing so. To watch the world's most skilled golfers turn occasionally into the rankest hackers was much more fun than getting out the chainsaws for a litde silviculture.46
This was a classic case of "seeing" the wind through instrumentation and devising ways to deal with it. In just such ways, engineers can predict worst cases and best cases and use probability theory to devise protections against bad outcomes and uses for the good ones. Predicting when they'll happen, and at what intensities, however, turned out to be far more difficult. Variables can be subtle and hard to see; effects can be dramatic.
Weather forecasts are erratic for very good reasons.
CHAPTER FIVE
The Art of Prediction
Ivan's story: Ivan hurried into hurricane status in three days, a full day faster than the official forecast. The transition came early in the day of September 3, when Ivan was still 1,210 miles east-southeast of the Lesser Antilles, at latitude io° and longitude 430. At five A.M. eastern time maximum winds were already 73 miles an hour, just marginally a hurricane, but by the end of the day the pressure had deepened sharply and sustained winds were already over 123 miles an hour—a strong Category 3 hurricane, nearly a Category 4. Such rapid strengthening at such low latitudes had not been observed before.
"Unprecedented" was the National Weather Service's measured word for the phenomenon. It looked as though the people of the Antilles, Puerto Rico, and Hispaniola all had a pretty good chance of a direct hit. The official forecast, based on numerous computer models, skirted Puerto Rico to the south and Jamaica to the north, and tracked right through Haiti and the Dominican Republic. If so, it would miss Cuba's south