Wednesday, October 25, 2006

Could Saharan Dust Storms Slow Hurricane Season?

No one would have believed, in the last years of the 19th century, that human affairs were being watched keenly and closely by intelligences greater than man’s and yet as mortal as his own.

So begins the H.G. Wells classic The War of the Worlds, the story of an alien invasion of our planet. Equipped with giant machines and powerful weapons, the Martians carve a path of destruction through England.

Yet, in the end, the alien invaders are defeated, not by the “weapons and guile of man, but by the simplest of all things, tiny microbes” which the Martians lacked any resistance.

In Wells’ timeless science fiction novel the Martians learned the hard way that one should never underestimate the power of something small. Now, researchers studying hurricanes are applying those same principles when it comes to Saharan dust. Tiny specks of dust may be suppressing hurricane activity just like the microbes that brought down the Martian machines.

Researchers at the Hurricane Research Division in Miami and the University of Wisconsin studied the past 25 years of satellite data of the Atlantic Ocean. They found that during times of intense hurricane activity the large clouds of dust that periodically blow westward from the Saharan Desert are relatively scarce.

Yet, in years when they are few hurricanes, the dust storms were stronger and tended to spread over much of the Atlantic Ocean and Caribbean Sea.

“The research is still in its infancy,” said James Dunion, a hurricane researcher at the Hurricane Research Division. “The results of the most recent study are very encouraging.”

In 2002, Dunion developed a technique for detecting the large dust clouds by using special infrared imagery from weather satellites. Since then, Dunion and researchers at the University of Wisconsin have been looking at the large dust clouds and their impact on hurricanes.

This past summer Dunion and his colleagues conducted new research in the eastern and central Atlantic. Using Hurricane Hunter aircraft, Dunion’s group flew eight missions to study the interactions between developing hurricanes and Saharan dust storms.

“We were able to focus our efforts over a part of the ocean basin that is rarely sampled by aircraft,” said Dunion. “Yet, this area (in the eastern Atlantic) is the breeding ground for hurricane seedlings that account for over half of the tropical storms and hurricanes that we see in the Atlantic each year.”

Some of the most powerful hurricanes in history have formed in the eastern Atlantic Ocean. Storms like Andrew, Camille and, most recently, Frances, all began life as a tropical disturbance in the eastern Atlantic.

“This research has helped us learn more about what causes hurricanes to intensify or weaken,” said Dunion.

The Saharan dust storms are part of a feature called the Saharan Air layer (SAL). SAL outbreaks tend to be most intense in the early summer and are responsible for ejecting vast amounts of dry, dusty air into the Atlantic throughout the hurricane season.

Some of the dust storms can cover an area the size of the lower 48 states and can travel as far west as Central America, the Gulf of Mexico and here in South Florida.

Dunion will spend the coming months analyzing his data trying to understand how the various workings of the dust storms-dry air, strong winds and suspended dust-can act to suppress hurricane formation and intensification.

Like those tiny microbes that conquered the Martin invaders in Wells’ science fiction classic, Dunion hopes to discover how tiny specks of dust can bring down the great storm on Earth.

Posted at 12:10 PM