As Charles Darwin neared the Cape Verde Islands off the west coast of Africa at the beginning of his famous voyage aboard the Beagle in 1832, he would write about clouds of dust powdering the ship, covering navigational instruments and stinging peoples‘ eyes. One hundred seventy-four years later, researchers at UW-Madison from the Cooperative Institute for Meteorological Satellite Studies (CIMSS) have discovered a link between the same dust storms that plagued the Beagle and the ferocity of hurricanes in the Atlantic Ocean.

Only this time, the dust elicits no tears. A CIMSS study published in October 2006 shows that large amounts of dust, which blow west from the Sahara Desert to the Atlantic Ocean, are present during periods of quiet hurricane activity, and vice versa–a link that suggests dust clouds may cripple the tempest.

Darwin never knew his good fortune.

Researcher Amato Evan standing before satellite dish on top of the Atmospheric, Oceanic and Space Science Building, where he conducted his research.

The finding begs the question, "Will this link help forecasters predict hurricanes?” Not yet, according to Amato Evan, assistant researcher at CIMMS and lead author of the study, but that capability is where he hopes to go with future research.

"If we can predict dust activity three or four months ahead of time, maybe then we can also predict some element of the hurricane activity,” Evan says.

Researchers have long debated the effects of global warming on hurricane activity, but no one has ever suggested anything like this. Although still in the early stages of research, Evan believes dust storms are another part of the big picture.

"It makes sense that the dust storms would be having some kind of an effect on the [hurricanes],” Evan says. "When I saw an increase in hurricane activity, I saw a decrease in dust activity. And for other years when there was a big increase in dust activity, I saw a decrease in the hurricane activity.”

Evan explains dust storms affect three of the many conditions favorable for hurricane formation. These hurricane-friendly conditions are (1) air that gets cooler with height, which causes the rapid mixing of air; (2) uniform wind speed with respect to height, which keeps the storm level and (3) high humidity, which condenses to form clouds and rain.

On the other hand, dust storms are characterized by (1) warm air at high elevations, (2) fast air at high elevations (a condition known as wind shear) and (3) dry air. The warm air creates an inversion–it acts as a blanket to reduce the temperature change between low and high, thereby reducing the potential for mixing. The fast elevated air tilts the storm, and the dry air prevents the formation of clouds and rain. Like adding a base to an acid, these dust storm characteristics help neutralize brewing storms.

Chris Velden, researcher and leader of the CIMSS team, and Jason Dunion, a National Oceanic & Atomospheric Administration (NOAA) researcher, coauthored the study and were the first to find a few isolated cases showing the link. Evan took the study one step further, blowing the dust off of 25 years of satellite data to show that the link was recurrent and dependable.

This was not an easy task. To researchers sifting through satellite data, dust clouds often looked like regular clouds. Andy Heidinger, researcher for NOAA’s Satellite and Information Service and CIMSS and also another co-author of the study, spent six or seven years tinkering with computer algorithms to detect dust clouds in satellite data; the amount of dust he found was astonishing.

A single dust storm contains quantities of dust comparable to the 540 million tons of ash that were coughed up by the eruption of Mount Saint Helens in 1980. The volcano’s hiccup darkened the sky for almost two weeks, forcing nearby airports and highways to close due to poor visibility and settling ash.

Darwin can relate.

"Generally the atmosphere is hazy,” Darwin reported in the Voyage of the Beagle. "This is caused by the falling of impalpably fine dust, which was found to have slightly injured the astronomical instruments. The dust falls in such quantities as to dirty everything on board and to hurt people’s eyes.”

Evan says these dust storms affect sunsets as far away as Florida, Puerto Rico and the Caribbean, and they may even contribute to the asthma and other respiratory problems of some people in this region.

"One dust storm can basically cover more than half of the Atlantic Ocean,” Evan says.

Darwin’s reached a similar conclusion.

"I have found no less than fifteen different accounts of dust having fallen on vessels when far out in the Atlantic,” Darwin wrote. "It has often fallen on ships when several hundred, and even more than a thousand miles from the coast of Africa, and at points sixteen hundred miles distant in a north and south direction.”

It is no surprise that these massive clouds of dust may possess the power to stifle a brewing hurricane. What’s not entirely clear yet are the forces that cause the periodic changes in dust activity.

"We really don’t know what causes dust activity to change from one year to the other, so that’s kind of the next big unknown,” Evan says. "It’s probably related to ocean temperature, but it’s also probably related to other things like maybe even vegetation density in the Sahel region. It might be related to how much it rained the year before in that area. There’s only been a little bit of work on that, so we’re really not totally sure, but that’s what I’m starting to try to do now.”

Evan hopes to continue his research so that he may come to understand the driving forces behind the dust. While hurricane forecasting is still just a hope for the future, the idea that dust storm and hurricane activity are inversely related introduces a possible new approach to the problem.

So if you’re ever sailing across the Atlantic and your ship is caught in a dust storm, be thankful for the dust in your eyes–it may have foiled a hurricane bent on sending you to Davy Jones’s locker.