Smoke plumes unlike anything previously seen…
More than 3.1 million acres have burned in California this year, part of a record fire season that still has four months to go. A suffocating cloud of smoke has veiled the West Coast for days, extending more than a thousand miles above the Pacific. And the extreme fire behavior that’s been witnessed this year hasn’t just been wild — it’s virtually unprecedented in scope and scale.
Fire tornadoes have spun up by the handful in at least three big wildfires in the past three weeks, based on radar data. Giant clouds of ash and smoke have generated lightning. Multiple fires have gone from a few acres to more than 100,000 acres in size in a day, while advancing as many as 25 miles in a single night. And wildfire plumes have soared up to 10 miles high, above the cruising altitude of commercial jets.
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Scientists have been scrambling to collect as much data on these wildfires as possible, hoping to unlock the secrets to their extreme behavior and fury. Among them is Neil Lareau, a professor of atmospheric sciences in the department of physics at the University of Nevada at Reno. Lareau closely studies pyrocumulus clouds, towering explosion-like plumes of heat that develop above intense blazes.
He retrieved data from the National Weather Service’s network of Doppler radars, which scan the skies every few moments at up to 15 different vertical angles. By stitching these different elevation “slices” together, he was able to produce a three-dimensional model of each smoke plume.
Wildfires and smoke plumes towering to new heights
The Creek Fire, which has burned nearly 200,000 acres in the Sierra Nevada mountains, was only 6 percent contained on Friday. On Sept. 5, a day after it was first ignited, its smoke plume soared to 55,000 feet. That’s taller than many of the tornadic thunderstorms that roll across Oklahoma and Kansas each spring.
Such clouds are both indicators of and contributors to extreme fire behavior, such as rapid fire spread and the formation of fire vortices including tornadoes, along with other dynamics that are hazardous to firefighters and can imperil communities.
“Anecdotally, this is the deepest that I’ve seen,” said Lareau, who was shocked by the height achieved by the smoke plume. “It’s about a solid 10,000 feet higher than we’re typically seeing with the highest of these plumes.”
A heat wave and dry winds fuel wildfires in the West
Lareau says the extreme height is a testament to the fire’s rapid spread and release of heat.
“[That], as well as the large burning area, results in the total amount of heat being injected into the atmosphere just being tremendous,” said Lareau.
He also noted that the record-shattering heat wave in California, which brought Los Angeles County’s hottest ever measured temperature of 121 degrees on Sept. 6, also played a role in the “tremendous plume depth.”
A pocket of air will rise so long as it is warmer than its surroundings. Ordinarily, thunderstorm tops stop their vertical ascent at the tropopause, the threshold of the stratosphere, where environmental temperatures begin warming with height.
“But we’re beneath a record-setting ridge,” said Lareau, describing the strong high-pressure system that brought the record warmth. Because the air is so warm, it expands, causing the atmosphere to grow in height vertically.
“That’s going to have very high tropopause heights,” Lareau. “The background structure of the atmosphere and having these record … heights sets up the opportunity to have this really remarkable plume depth.”
Wildfires brew extreme fire behavior
In addition to the extreme fire heights, tornadic vortexes have been spotted by radar within three of this year’s colossal fires. The first, the Loyalton Fire in Lassen County, Calif., even prompted the National Weather Service to issue its first-ever fire tornado warning on Aug. 15.
Before 2020, only a few fires had ever produced documented fire tornadoes in the United States; now we’re seeing them every week or two. Lareau says the tremendous heights of the wildfires’ clouds, combined with more concerted and astute observation, are factors in the numerous fire tornadoes that have been reported this year. He thinks there may be some also truth to the apparent increase.
“We have a ton of eyes on every fire, looking at every frame, but still, we weren’t seeing these before,” he said. “And we’re seeing all too much of it right now. It’s rather worrying.”
The extreme fire behavior is so foreign and jarring that Lareau has found it a challenge to place it in context.
“These are still real outlier events,” said Lareau. “The way I’ve been trying to think about it, if it’s a 1 in 100 event, now we have, what, 7,000 fires on the landscape? The opportunity to experience these extremes of fire weather are off the charts right now.”
Similarities to past events
The North Complex West, burning in the Sierras of California, bears striking similarities to the Carr Fire of 2018. That inferno, which produced a deadly fire tornado near the city of Redding in Northern California, killed three firefighters and five civilians.
“I think [they’re] almost carbon copies of one another,” said Lareau. “You have the exact same direction of travel, same wind dynamics, same terrain, same fuels, very similar fire behavior.”
The Creek Fire, located farther south, has produced a number of clockwise-spinning fire tornadoes. That’s opposite to how most tornadoes spin in the Northern Hemisphere. Lareau is working with meteorologists from the National Weather Service, as well as research colleagues, to develop a conceptual model of how these rotating fire and smoke plumes behave.
He hopes that, in the not-too-distant future, it may be possible to forecast these events and issue warnings in advance.
Searching for a new understanding
While the radar animations Lareau produced are as aesthetically captivating as they are scientifically illustrative, he hopes that higher-resolution data, which is much tougher to come by, would provide atmospheric scientists with clearer insight as to how these fires behave under the hood. Ideally, he would target wildfires with ground-based mobile Doppler radars and remote sensing instruments mounted aboard aircraft.
“We’ve been proposing for three or four years now to do major field campaigns targeting these extreme behaviors,” said Lareau. “We’ve been arguing to the community that these are really vital data to collect.”
Thus far, funding has not been secured, but Lareau is hopeful.
“We really need to advance our understanding about what’s going on with the high-end fires.”
Andrew Freedman contributed to this report.
Published at Sun, 13 Sep 2020 19:25:43 +0000