Dust and Hurricanes

Dust may dampen hurricane fury

"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."


University of Wisconsin-Madison

Public release date: 10-Oct-2006

Contact: Jonathan Foley




MADISON - After more than a dozen hurricanes battered the Atlantic

Ocean last year, scientists are wondering what - if anything - might

be causing stronger and more frequent storms.


Some have pointed to rising ocean temperatures, brought on by global

warming. Others say the upswing is simply part of a natural cycle in

which hurricanes get worse for a decade or two before dying down



Now, researchers at the University of Wisconsin-Madison have put

forward an intriguing theory that introduces a whole new dimension to

the debate.


Writing today (Oct. 10, 2006) in the journal Geophysical Research

Letters, the scientists discuss a surprising link between hurricane

frequency in the Atlantic and thick clouds of dust that periodically

rise from the Sahara Desert and blow off Africa's western coast. Lead

author Amato Evan, a researcher at UW-Madison's Cooperative Institute

for Meteorological Satellite Studies (CIMSS), pored over 25 years of

satellite data - dating from 1981 to 2006 - and noticed the

correlation. During periods of intense hurricane activity, he found,

dust was relatively scarce in the atmosphere. In years when stronger

dust storms rose up, on the other hand, fewer hurricanes swept

through the Atlantic.


"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 UW-Madison'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." 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



Researchers have increasingly turned their attention to the

environmental impact of dust, after it became clear that in some

years, many million tons of sand rise up from the Sahara Desert and

float right across the Atlantic Ocean, sometimes in as few as five

days. "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 west into the northern Atlantic. Dust storms form primarily

during summer and winter months, but in some years - for reasons that

aren't understood - they barely form at all.


Evan decided to explore the correlations between dust and hurricane

activity after CIMSS research scientist Christopher Velden and others

suggested that dust storms moving over the tropical North Atlantic

might be able to suppress the development of hurricanes.


The UW-Madison researchers say that makes sense because dry,

dust-ridden layers of air probably helps 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

unfortunately means it would have a higher chance of hitting U.S.



While the UW-Madison work doesn't confirm 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."