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
jfoley@wisc.edu
608-265-9119
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
again.
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
time.
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.
land.
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."
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