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August 1998

A perfect match: WiFE and wildfires

The NCAR/NSF C-130 will be circling and sampling wildfires throughout the western United States later this summer and fall.

Recent scorching heat across the Intermountain West is setting the stage for an unusual NCAR field project later this summer. The Wildfire Experiment (WiFE) will bring the NSF/NCAR C-130 aircraft to "fires of opportunity" in the West. Staff from the Mesoscale and Microscale Meteorology Division (MMM), the Atmospheric Technology Division (ATD), and the Atmospheric Chemistry Division (ACD) will be pitching in to sample the fires photographically and chemically with a unique batch of airborne sensing tools. Also providing instruments, scientists, and observers are NASA Ames Research Center and the U.S. Forest Service's Rocky Mountain Research Station and Riverside Fire Research Laboratory.

Much of the inspiration for the NSF-funded WiFE comes from dramatic modeling results obtained by Terry Clark (MMM) and colleagues in recent years. After developing one of the world's most comprehensive atmosphere/fire models, Terry and MMM's Janice Coen have uncovered small-scale structures in fire at its most explosive. Now ATD's Larry Radke is on board to provide field expertise. Larry has sampled some mean fires in his day, including the oil-fueled infernos that followed the Gulf War of 1991 in and near Kuwait.

"What Terry and I are interested in is fairly violent, unpredictable fire behavior," says Larry, "the kind that kills firefighters and confounds prediction efforts."

Wildfires cost lives and hundreds of millions of dollars per year across the West. When conditions are right, a modest fire can quickly flare into a disaster, as happened near Glenwood Springs on 6 July 1994, when 14 firefighters perished. Experience and modeling have combined to show that such events are especially likely in negative wind shear: strong winds near the ground (moving at the leading edge of a microburst or gust front, or created by the fire itself) combined with lighter winds aloft. "Our simulations show that negative wind shear can produce extreme fire behavior, such as rapid intensification of fire-line dynamics, strong fire whirls, erratic spread rates, and strong updrafts that can loft burning embers ahead of the fire," Janice says. She is studying how these simulated blow-ups occur by examining intense horizontal vortices that form at the base of fire-line updrafts.

Last summer, Larry and Terry took part in a pre-WiFE engagement, the International Crown Fire Modeling Experiment. (Crown fires are those that spread--often quickly and intensely--across the tops of trees.) In June-July 1995, fire researchers from Canada, the United States, Russia, and Germany set a series of experimental crown fires in a jack pine forest in Canada's Northwest Territories to gain a better understanding of high-intensity crown fire behavior. Among the devices that monitored fire spread rates, vertical temperature profiles, flame geometry, and radiation flux was NCAR's new Thermacam, which has given the best insight to date into the small-scale dynamics of intense wildfires.

Here's a truly superficial impression of Larry Radke. The sensitive Thermacam used in WiFE to study wildfire is measuring the temperature of Larry's facial skin and glasses.

The Thermacam, a digital infrared imager built by Inframetrics, Inc., is literally the coolest instrument in WiFE. The compact camera houses a minirefrigerator to keep its sensitive array of radiometers at a crisp -321degreesF (-196degreesC). The extreme cold provides a more stable reference point from which the array can map temperatures to as high as 2,700degreesF (1,500degreesC) at a resolution of three feet (one meter) across a field of flame. "I'm thrilled by the things it can see," says Larry.

Complementing the Thermacam for infrared sensing will be ATD's airborne imaging radiometer, specially adapted by Craig Walther and Peter Hildebrand so that its microwave beams can sense higher temperatures than ever before (up to 3,600degreesF, or 2,000degreesC). This radiometer will be looking at more than flame. Fuel type is a key variable in wildfire prediction, and the moisture content of biomass helps determine volatility. The ATD radiometer, when used in polarized mode, will be able to sense biomass amounts as well as their moisture content.

The chemistry of fire (and fish)

NCAR chemists will be studying the array of emissions sent up by the burning biomass. Hans Friedli (ASP) is coordinating this part of WiFE. One of the chemicals of interest is mercury, which forest fires may be transferring from vegetation and soil to the atmosphere. Mercury moves readily through the environment, whether it originates from natural sources (such as oceans and volcanoes) or anthropogenic ones (such as power plants, waste incinerators, and mining operations).

"Mercury is showing up in remote areas of the world, such as the Arctic, far from emissions sources, and it accumulates in fish to such a degree that it becomes a health hazard for people depending on fish as a staple food," says Hans. "Wildfires may contribute to this problem." ACD will be collaborating with marine scientist William Fitzgerald (University of Connecticut), a world expert on mercury migration and analysis. Support for the mercury sensing is pending from the Electric Power Research Institute.

Also from ACD, Elliott Atlas and members of the division's stratospheric/tropospheric measurements group plan to sample methyl halides (bromide, chloride, and iodide) and other organic compounds emitted from forest fires. One of these compounds, methyl bromide, has both industrial and natural sources, so researchers are trying to determine the emissions for each group. Natural sources (grassland and forest fires) may comprise 20-30% of methyl bromide emissions, says Elliott. "As far as I know, there's been less work with forest fires, especially outside of the tropics, than with grass fires [for these compounds]. We expect there may be some significant differences in emissions from different regions and from different vegetation types." Elliott is also studying the overall fingerprint of organic emissions from biomass burning, including a variety of unsaturated hydrocarbons and oxygenated organic molecules that contribute to the chemical reactivity of the fire plume.

Meanwhile, ACD's Teresa Campos will be measuring carbon dioxide at two sampling rates. "Combined with methane and carbon monoxide information from Elliott's measurements, we can determine the fire's combustion efficiency," says Teresa. The data will also help clarify the amount of total carbon emitted from such fires. While the majority comes from CO, CO2, and methane, trace gases such as mercury and methyl halides also contribute to the carbon emissions.

"We don't get a chance to explore big fires very much," notes Elliott of ACD's involvement in WiFE. "It's a program of opportunity for us."

A convenient collaborator

The federal unit that oversees firefighting coordination for the Rocky Mountains happens to be located next door to ATD's Research Aviation Facility (RAF) at Jeffco. NCAR will work with this office, the Intermountain Fire Coordination Center, to determine which fires to go for. WiFE will attempt four to five flights over six weeks, beginning around the first of September (fire-weather permitting). At-risk areas may be known ahead of time, but exact destinations may remain a mystery until a given fire flares up on the morning of departure.

"The C-130's speed, range, and endurance will allow us to be over any wildfire in the United States in less than a day," write Larry and Terry in WiFE planning documents. "We can observe and return home all in the same day without refueling. This should greatly improve our otherwise rather poor chances of observing a wildfire at a dramatic and dangerous phase." Each flight will generally circle around a fire counterclockwise at several kilometers' altitude and at no more than 150 knots. The Thermacam will be collocated with a small video camera pointing out the left window bay of the C-130.

For safety, all three RAF pilots (Henry Boynton, Lowell Genzlinger, and Mike Heiting) will be on board for each marathon flight. A full RAF support team (Dick Friesen, Al Schanot, Norm Zrubek, Krista Laursen, Dick Taylor, and Mike Spowart) will assist from ground level.

This project could be NCAR's first WiFE of several, says Larry. "Success in this test phase will not only encourage us to continue the program into coming years, but new knowledge also will guide us in further integration of observational tools and in making the fullest use of the C-130's capabilities for fire-weather and attendant air-pollution research."

Insight from WiFE could help save both money and lives, according to its leaders. If this year holds true to form--and July's weather hinted that it would--some 5 million acres of the West will go up in flames. "As urbanized America continues to spread into the woods," notes Larry, "the cost of such incidents is only going to rise." •BH

QuickTime movies from the International Crown Fire Modeling Experiment can be found through Canada's on-line publication Geos,

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Edited by Bob Henson, bhenson@ucar.edu

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