Scientists hear power of hurricane

Researchers at MIT think that they may be on to a better, cheaper way of detecting the power of a hurricane – simply listen to how strong it is.

Flying into the eye of a storm is effective, but expensive – maybe listening would give just as much information.

Currently there is only one way of measuring the strength of a hurricane – send an aircraft through the most intense winds and into the eye of the storm, carrying out wind-speed measurements as they go. This is an expensive way of detecting this vital information.

Nicholas Makris, associate professor of mechanical and ocean engineering and director of MIT’s Laboratory for Undersea Remote Sensing, thinks there may be a better way. By placing hydrophones (underwater microphones) deep below the surface in the path of an oncoming hurricane, it is possible to measure wind power as a function of the intensity of the sound.

“The roiling action of the wind, churning up waves and turning the water into a bubble-filled froth, causes a rushing sound whose volume is a direct indicator of the storm’s destructive power,” said Makris.

Makris has been doing theoretical work on this potential method for years. But now he has found the first piece of direct data that confirms his calculations. In a paper accepted for publication in Geophysical Research Letters, Makris and his former graduate student Joshua Wilson show that Hurricane Gert, in 1999, happened to pass directly over a hydrophone anchored at 800 meters depth above the mid-Atlantic Ridge, and the same storm was monitored by airplanes within the next 24 hours.

The case produced exactly the results that had been predicted, providing the first experimental validation of the method, Makris says.

“There was almost a perfect relationship between the power of the wind and the power of the wind-generated noise,” he says. There was less than 5% error - about the same as the errors you get from aircraft measurements.

He also says there is another benefit to his work. The hydrophones could be a very effective way of monitoring the amount of sea salt entering the atmosphere as a result of the churning of ocean waves. This sea salt, it turns out, has a major impact on global climate because it scatters solar radiation that regulates the formation of clouds. Direct measurements of this process could help climate modelers to make more accurate estimates of its effects.