A Way to Nail the Forecast

WE NEED ONLY look to last year's devastating hurricanes to realize how much we remain at the mercy of nature. And we're still not terribly good at predicting weather. But Charles Meneveau, a professor of mechanical engineering at Johns Hopkins University, working with graduate student Yi Li, has devised a mathematical formula that could lead to better computer models for predicting turbulent flow. Turbulence occurs when a gas or liquid flows chaotically. It's a common phenomenon that's hard to understand and predict. One characteristic of turbulence is intermittency, which is an abrupt, highly concentrated change of speed in a fluid's flow. These changes are fairly rare, but when they happen, they can be very violent. They're hard to track using computer models because they require vast numbers of calculations and enormous computing power. But Meneveau and Li's "advected delta-vee equation" is a simple formula that's a shortcut for predicting intermittency. It instead tracks two particles as they move through turbulence, not unlike a pair of balloons being buffeted by wind gusts. They hope it can be used in models to not only predict movement within bodies of water but also weather patterns. -TG

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