SAN FRANCISCO — The dark pall of smoke hovering above recent giant forest fires yielded a scientific bonanza for researchers studying if atomic warfare would plunge Earth into a freezing "nuclear winter."
"The conditions that existed in southern Oregon and Northern California were as close as one is likely to see to conditions one might expect after the use of nuclear weapons," said Bernard Zak, atmospheric program coordinator at Sandia National Laboratories in Albuquerque, N.M.
The fires yielded "at least 10 times as much data" as last year's highly publicized and much-studied controlled brush fire in the San Dimas Experimental Forest northeast of Los Angeles, said Zak, a physicist funded by the Defense Nuclear Agency.
"Fire and smoke began to approach the regional scale we expect to see after a nuclear war, although certainly didn't come anywhere close to the global scale," said Richard Turco, a Marina del Rey atmospheric scientist.
"The fires have given us our first real data on these scales," said Turco, who helped develop the theory that smoke from cities bombed during even a limited nuclear exchange would block sunlight long enough to freeze the Northern Hemisphere, possibly wiping out crops and causing mass starvation.
Scientists said information gathered from the fires hasn't been analyzed, but will be used to help determine if the nuclear winter hypothesis is correct.
"We haven't found anything that's tending to knock the props out from under it," said University of Washington atmospheric physicist Lawrence Radke.
Turco said information collected from the fires also will help researchers studying acid rain, depletion of Earth's protective ozone layer and the "greenhouse effect" warming of the atmosphere.
The fires, some of which are still smoldering 1 1/2 months after being ignited by lightning strikes in late August, engulfed 772,500 acres in Northern California and 135,281 acres in southern Oregon, U.S. Forest Service spokesmen said.
"It's terrible all the natural destruction occurred, but it's fortunate we could make some aircraft-based measurements in the smoke to help us understand the nuclear winter hypothesis better," said Pennsylvania State University meteorologist Douglas Westphal.
Zak said scientists were in Seattle in late August waiting to study intentionally set fires, but flew south because "some of the most massive wildfires seen in decades were going in Northern California and southern Oregon."
As smoke turned daylight to twilight throughout the region, scientists conducted two key experiments. Sandia's Twin Otter aircraft sampled cumulus clouds that formed above large smoke plumes, while UW's C-131 research plane chased a huge smoke plume 400 miles over the Pacific Ocean.
"No one's ever tracked a smoke cloud that far before," Turco said, adding the chase let scientists get information on how long smoke particles take to clump into larger particles and how fast they fall.
"People who are pooh-poohing nuclear winter are saying the smoke particles are going to get large enough that they'll fall out," said Westphal, who works under contract to the National Aeronautics and Space Administration.
But early findings suggest "the nuclear winter hypothesis is actually looking pretty robust," Radke said.
Scientists also studied how much sunlight and reflected heat was absorbed and how much was scattered by smoke particles--key questions in determing if smoke from nuclear war would cool the planet's surface, said Dean Hegg, a University of Washington atmospheric chemist.
Turco said the Otter's sampling of clouds above other smoke plumes was the first such sampling done successfully.
Critics of the nuclear winter theory believe smoke particles will clump together in the clouds or be washed out by rain, reducing the sun-blocking effect. But Turco said smoke particles that "seed" clouds may be so numerous that only tiny fog droplets condense, preventing the washing effect.
"That seems to be what's happening," he said.
Zak and others cited unconfirmed reports that some smoke-covered valleys had temperatures in the 50s despite forecasts of 80-degree weather.
In 1982, University of Maryland meteorologist Alan Robock found smoke from Canadian forest fires chilled Midwest areas beneath the pall 3 to 7 degrees below forecasts, while adjacent non-smoky areas had temperatures consistent with forecasts. He now is attempting to learn if the same thing happened during the recent fires.
"The fires were awesome," Zak said. "The plumes towered to 15,000 to 20,000 feet. Whole hillsides were going up in flames in seconds. It was quite an emotional experience, particularly when one thinks of the men on the ground fighting those fires."