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| During their flights aboard the Twin Otter
to measure the interactions between the boreal forest and the lower
atmosphere, the BOREAS team encountered eight vortices during the summer
of 1994—an average of one for every 1800 km (1100 miles) flown
(MacPherson and Betts 1997). They ranged in diameter from 150 to 300
meters (500—1000 feet), and reached some 1500 meters (5000 feet) in
height.
Functioning a little like "mini-tornadoes," these vortices provide a mechanism in low wind conditions for the surface to transfer enormous amounts of heat and carbon dioxide up into the atmosphere. The BOREAS team measured fluxes of heat and carbon monoxide anywhere from 30 to 60 times greater than average during these vortex events. "The vortices are a kind of dry-air convection,"
Betts says. [Here, "convection" refers to the upward motion
of warm air, which rises because it is less dense than adjacent cooler
air, just as warm air rises above a wood stove.] |
 Small atmospheric vortices in arid regions, like this one in Australia, are called "dust devils." In the boreal forests there are few fine dust and sand particles to be lofted into the air by vortices, so they remain invisible, threatening low-flying aircraft. (Photograph by John Roenfeldt, courtesy Australian Severe Weather) | ||
 "There are a number of different ways in which the atmosphere organizes to transfer heat away from the surface," he adds. "The fact that the boreal ecosystem uses these vortices is an interesting curiosity—but very important when you’re flying 20 meters above the forest canopy." References
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A column of rising warm air forms the center of a vortex, surrounded by spiraling winds. (Diagram courtesy Mars Pathfinder Project, Jet Propulsion Lab) | ||
Improving the Forecast Models
