What's it like inside a whirling dust devil?

"Very dusty," according the Dr. Jim Gilreath of the University of Florida's Gulf Coast Research and Education Center in Bradenton, Florida. "You don't want to get in one," he assured us. "The dust is very fine and it gets everywhere - in your eyes and ears and your nose. If your mouth is open, you'll get a lungful. Nasty stuff."

Dust devils differ from "dust plumes," which do not rotate, and "debris clouds" which contain heavier debris and often form beneath a condensation funnel at the base of a tornado. Unlike tornados, dust devils can spin in either a clockwise or counterclockwise direction regardless of which hemisphere they are in. Dust devils rarely cause damage, but occasionally, a dust devil can produce hurricane force winds exceeding 75 mph.

Dr. Gilreath's work puts him in just the right circumstance to know dust devils intimately. He and others are looking for alternatives to the soil fumigant methyl bromide. Methyl bromide has been identified as an ozone depleter, and the United States has agreed, as part of the international treaty known as the Montreal Protocol, to phase out its use by 2005. For some crops, alternative pest and weed control fumigants are available. But for others, such as peppers, cut flowers, and gladiolus, an effective alternative to methyl bromide fumigation has been more elusive.

One of the crops in Dr. Gilreath's research is caladiums - which happen to be rather picky plants with rather specific growing conditions. Used as ornamental plants because of their colorful, heart-shaped leaves, they are sold as a tuber. About 95% of the caladium tubers in the world are grown at Lake Placid, Florida. Dr. Gilreath explained that the conditions in Lake Placid that make for such ideal caladiums also make for ideal dust devil creation. The soil around Lake Placid is called by the not-so-scientific moniker of "muck." It is very high in organic material which decayed eons ago in swamp lands. The organic deposits can be as deep as 12 feet. Spring in Lake Placid is usually dry, cloudless, and very warm. The dark, rich, organic soil readily absorbs and radiates heat back into the air. The rapidly rising warm air meets cool breezes coming in from the Florida coast, and voila, weather occurs! As all weather buffs know, when warm air meets cool air, instability is the net result. A mini-low pressure system forms and dust devils are born. Dr. Gilreath has seen as many as six columns of dust in one field. They zigzag across the field gathering up a tube of the light organic dust, often going right off into the grass at the field's edge.

Dr. Gilreath was not the only one to find out what it's like to stand in the path of a dust devil. One of his trusty Davis EZ-Weather Monitor II weather stations was damaged by one, even though the tripod was anchored by metal spikes reaching three feet into the soil. On this particular day, methyl bromide had been injected into a field of 30 or 40 acres. After injection, the field was covered with strips of thin plastic film which are glued together to form one gigantic sheet covering the entire field. As the wind blew across the sheet, slow undulations began to form and grow steadily until huge waves of plastic rose eight feet into the air.

"Suddenly a large dust devil formed, tore across the rippling plastic and wrapped the poor weather station in a big glob of plastic," Dr. Gilreath recalled. "Even though the tripod was spiked into the ground, the force of the wind and the plastic bent the tripod's legs right over."

Of course, the EZ-Weather Monitor II, once its tripod legs were straightened, went right back to gathering data from the grower's field for Dr. Gilreath to download and study. Dr. Gilreath's research weather stations stay in grower's fields for the two or three years during which he studies each field.

"I usually end up giving the grower the station when I'm done with one field. They get used to being able to check the temperature and rainfall every day, and leaving the station is a way to thank them for letting me use their field for my research," said Dr. Gilreath. "One grower, however, probably won't get to keep his weather station since one of his workers ran over it with a tractor…."

Between dust devils and snoozing tractor operators, Dr. Gilreath is one Davis customer who really appreciates our high quality products. Even his home station should be getting hazard pay, as Dr. Gilreath's home is in the middle of an orange grove, and there the problem is not dust devils, it's lightning. But that's another story altogether…

Want to learn more about methyl bromide? Visit the Methyl Bromide Phase Out Web Site at http://www.epa.gov/ozone/mbr/mbrqa/html

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