In southern Oregon, the Bootleg fire has now burned a swath of land larger than the city of Los Angeles. It has forced at least 2,000 residents from their homes and burned 160 houses and buildings. And it’s not alone – there are more than 80 fires burning across the United States.
Some of these fires are now so intense and large they can create their own weather systems, including fire tornadoes, clouds and other weird phenomena – including smoky haze that has reached New York City, 3,000 miles from where the fires started. New York City now has some of the world’s worst air quality, prompting state officials to issue an alert for residents with underlying health conditions, such as asthma, to avoid the outdoors.
The clouds can create smoke updrafts called pyrocumulus clouds – which happens when hot air rises, leaving a vacuum behind that the fire rushes in to fill. Some researchers have compared them to volcanic eruptions. They often look like giant, dirty-colored thunderheads that sit atop a massive column of smoke from a wildfire.
Researchers from the Naval Research Laboratory say they have been tracking record numbers of an even larger type of fire cloud called pyrocumulonimbus – also known as the fire-breathing dragon of clouds. A cumulonimbus without the “pyro” part is imposing enough – a massive, anvil-shaped tower of power reaching five miles high, hurling thunderbolts, wind and rain, 根据 Nasa.
Over the past two weeks, researchers have observed pyrocumulonimbus plumes generated by fires in Alberta, 加拿大, Montana and Oregon. These fire-induced thunderclouds can inject massive amounts of smoke particles into the upper atmosphere, and produce lightning, hail, but little-if-any actual precipitation. The Bootleg fire started producing its own lightning last week, 根据 National Weather Service.
During the 2019-20 bushfires in Australia, blazes emitted an unprecedented amount of smoke about 10 miles high, three miles thick and more than 600 miles across – about the distance from Atlanta to Washington DC. Smoke traveled east to South America, and after dissipating covered the southern hemisphere, circumnavigated the globe. More than seven months after the initial brush fires, remnants of the plumes were still detectable, even at altitudes above 18 英里.
When they form above fires, pyrocumulonimbus clouds can make the blaze below spread even faster. Sometimes they can also create their own lightning, which can spark more fires. But in some cases, they can also cause rain.
In California’s Dixie fire this week, a pyro-cloud spun off lightning within the fire’s 40,500-acre footprint as it gained momentum early Monday afternoon, the National Weather Service said. It soon began shooting electric bolts at the surrounding area, where firefighters worked to contain the blaze. Meteorologists tracking the storm recorded 31 lightning strikes in all.
In addition to lightning, fire can also create tornadoes – a spiraling vortex of gases and smoke and fire.
“They’re rare, because you need a lot of buoyancy from heating of the air by very hot gases coming off the fire,” Loretta Mickley, a senior research fellow in chemistry-climate interactions at the Harvard John A Paulson School of Engineering and Applied Sciences, told the Harvard Gazette. “Wind shear together with the intense heat could generate a fire tornado, 哪一个, 顺便一提, sounds horrible.”
A fire tornado had winds as high as 140 miles an hour and was captured on video during the Carr fire near Redding, California, 在七月 2018. There are also some indications that the Bootleg fire has spawned fire tornadoes.
When the weather begins to cool into the evening, the clouds can pose a danger as they fall to the ground.
“Later in the afternoon, that cloud will collapse and create a downdraft of heavy smoke, embers, things like that, and it can actually create additional fire behavior,” Lisa Cox, a fire public information officer, told the Los Angeles Times. She added that the collapse can fling sparks miles ahead of the main fire. 同时, the smoke also reduces visibility, grounding firefighting aircraft, 她说.
Fuels – such as leaf litter and brush – are drier than in past years, making the fires hotter than ever. With no dampness around, the conditions for serious fire weather become more likely.
The paradigm for fire and weather is now flipped on its head – and the fires are starting to change the weather around them.
“The [Bootleg] fire is so large and generating so much energy and extreme heat that it’s changing the weather,” Marcus Kauffman, a spokesman for the state forestry department, told the 纽约时报. “Normally the weather predicts what the fire will do. In this case, the fire is predicting what the weather will do.”