They found that during periods of intense hurricane activity, dust was relatively scarce in the atmosphere, while in years when stronger dust storms rose up, fewer hurricanes swept across the Atlantic.
Amato Evan of the University of Wisconsin-Madison and colleagues there and at the National Oceanic and Atmospheric Administration studied 25 years of satellite data--covering 1981 to 2006--to establish the correlation. Their findings are published 10 October in Geophysical Research Letters.
"These findings are important because they show that long-term changes in hurricanes may be related to many different factors," says co-author Jonathan Foley, director of the university's Center for Sustainability and the Global Environment. "While a great deal of work has focused on the links between [hurricanes] and warming ocean temperatures, this research adds another piece to the puzzle."
Researchers have increasingly turned their attention to the environmental impact of dust, after it became clear that in some years, millions of tons of sand rise up from the Sahara Desert and float across the Atlantic Ocean, sometimes in as little as five days. If scientists conclusively prove that dust storms help to squelch hurricanes, weather forecasters could one day begin to track atmospheric dust, factoring it into their predictions for the first time, the researchers say.
"People didn't understand the potential impact of dust until satellites allowed us to see how incredibly expansive these dust storms can be," says Evan. "Sometimes during the summer, sunsets in Puerto Rico are beautiful, because of all the dust in the sky--well that dust comes all the way from Africa."
The Sahara sand rises when hot desert air collides with the cooler, dryer air of the Sahel region, just south of the Sahara, and forms wind. As particles swirl upwards, strong trade winds begin to blow them westward into the northern Atlantic. Dust storms form primarily during summer and winter months, but in some years, for reasons that are not understood, they barely form at all.
Evan decided to explore the correlations between dust and hurricane activity after his colleague and co-author Christopher Velden and others suggested that dust storms moving over the tropical North Atlantic might be able to suppress the development of hurricanes. The researchers say that this makes sense, because dry, dust-ridden layers of air probably help to "dampen" brewing hurricanes, which need heat and moisture to fuel them. That effect, Velden adds, could also mean that dust storms have the potential to shift a hurricane's direction further to the west, which means it would have a higher chance of hitting the United States and Caribbean islands.
While the current research does not establish that dust storms directly influence hurricanes, it does provide compelling evidence that the two phenomena are linked in some way. "What we don't know is whether the dust affects the hurricanes directly, or whether both [dust and hurricanes] are responding to the same large scale atmospheric changes around the tropical Atlantic," says Foley. "That's what future research needs to find out."
The study was funded by the National Oceanic and Atmospheric Administration.
Harvey Leifert | American Geophysical Union
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