Oh well, now there’s an outbreak of forest fire storm clouds

Last week the The US Naval Research Laboratory held a very 2021 press conference, during which scientists reported a very 2021 outbreak of “smoke storm clouds”. Catastrophic forest fires, exacerbated by catastrophic climate change, had produced an eruption of pyrocumulonimbus plumes over the western United States and Canada, known in scientific vernacular as pyroCb.

“You can think of them as giant chimneys, channeling the smoke released by the fire into a thunderstorm,” David Peterson, meteorologist at the research lab, said at the Zoom press conference. “You can imagine this extremely dirty thunderstorm, with all those smoke particles to make the water condense.”

Unlike a typical thunderstorm, however, the resulting water droplets do not tend to grow large enough to fall as rain. “But it’s a cloud that can produce a lot of lightning,” Peterson added. These clouds can then advance across the landscape, causing new forest fires as they go. So not only can the blaze spread by throwing embers past the main fire line (California wildfires are so deadly in part due to the strong seasonal winds that push them at incredible speeds), it can also spread. producing so much hot, rising smoke that it essentially recruits the atmosphere to start more fires for it. It’s a self-proliferating machine that gets carried away.

The plumes of pyrocumulonimbus will also energize the forest fire that spawned them. As the warm air moves away from the fire, the air near the ground rushes to fill the void, increasing the speed of the wind at the surface. But because a pyroCb is a thunderstorm cloud, it also produces a downdraft with this updraft, creating extremely irregular wind behavior near the surface. Basically, if you’re expecting a pyroCb-producing wildfire to behave rationally, traversing the landscape with the prevailing winds, you’ve got something else to come.

And these pyroCbs can be huge. The hotter a forest fire, the more upward air it produces. “These push the smoke upwards at extreme speeds, so they inject smoke at altitudes above the cruising altitude of the jets,” Peterson said. “So we’re talking about 50, 60,000 feet, potentially.” In fact, he says, the smoke will flow into the next layer of the atmosphere, the stratosphere, which sits above where the weather usually occurs. Peterson added that a pyroCb that formed in British Columbia in 2017 produced a plume that persisted in the stratosphere for 10 months.

Once all of these smoke aerosols have reached the stratosphere, they can have a contradictory effect. Because they can block the sun, they will cool the landscape below. But the plume itself will absorb energy from the sun, warming the air locally to create a “thermal bubble”. This creates a naturally aspirated engine that circulates the smoke, which scientists have dubbed a “vortex”. “So this little engine event, created due to the emission of smoke into the stratosphere, leads to its own stratospheric time,” Mike Fromm, of the remote sensing division at the US Naval Research Laboratory, told the conference Press. “It’s a whole new discovery, but it’s very real. And we’ve seen it now in a number of cases.

In late June, Peterson and Fromm tracked one of the largest pyroCb plumes ever recorded in North America. The formation of this type of cloud is perhaps not a bug but rather a characteristic of a climate which has become bizarre. “We’ve been in a wave of pyroCb activity in North America – almost daily activity for the past few days,” Peterson said. “This pyroCb outbreak is actually the latest in a series of pyroCb outbreaks that we have seen around the world in recent years.”

Australia’s terrible 2019-2020 bushfire season, for example, produced 38 of these plumes in just a few days. Siberia, of all places, has also spawned them as its landscape heats up, dries up and ignites. “There have been a lot, I would say, in the last few fire seasons,” says UCLA climatologist Daniel Swain. “And there are probably two or three different reasons for this.”