As piracy fires swept through south central Oregon, the Dixie Fire scorched Northern California and destroyed hundreds of thousands of acres of forest. The billowing flames ejected large amounts of smoke into the air. Normally, the smoke drifts a few kilometers above the ground, and then is blown across the country by the wind—like weather fronts that carry moisture and rain—shrouding New York City and the East Coast in a thick haze. middle.
But Bootleg has sent out a towering vertical plume, raising the smoke to a record 16 kilometers. Intense heat from high-density fuel; local weather conditions and dry surfaces; and high-altitude atmospheric clouds, which together cause plumes to be much higher than ordinary clouds. When you see these scorched cumulonimbus or scorched cumulonimbus, you know that you are in big trouble below.Also known as short for pyroCb, these clouds are so strong that they Modify local weather, For example, producing strong storms and producing amazing lightning storms can ignite more fires.
In recent years, the fire, its haze, and the towering smoke and thunder formed above it have become more and more familiar sights. However, we are only just beginning to understand what causes these awesome “fire clouds”, the ingredients in them, and their impact on weather and climate. By combining field observations, laboratory experiments, and computer modeling from local to global scale, our team at Los Alamos National Laboratory is understanding the mechanism and climate of cumulonimbus caused by the recent catastrophic fire in British Columbia (2017) Progress in impact, Australia (2019-2020).
This work has brought two benefits. It will give us a clearer understanding of what is driving climate change and will help us develop more effective computer tools to extinguish fires and reduce their dangers.
The heat of hell
Pyrocumulonimbi has a story to tell. Visible in the stratosphere higher than Everest, these billowing clouds of smoke, moisture and gas only appear above the largest fire, like the heat of hell. They attacked fiercely with lightning and even fire tornadoes, turbocharged the local winds, and powered the fire to flood the unburned area. This year, a fire in British Columbia resulted in 700,000 lightning strikes, which is equivalent to the number of lightning strikes that normally occur in BC in a year. The 2017 fire in British Columbia produced five fiery cumulonimbus clouds in one day, injecting more than 220,000 tons of smoke into the lower stratosphere in just five hours.
That’s not all. By injecting soot and other particles collectively known as aerosols into the stratosphere—a high atmosphere starting a few miles above the earth—thermocumulonimbus clouds may temporarily change the climate away from the fire. The smoke prevents warm sunlight from reaching the earth and lower atmosphere. In addition, black carbon or soot can absorb sunlight and heat the air to make it rise higher. This effect was discovered by the late Robert Malone of Los Alamos in 1985 and has been confirmed by observations. New research It was found that the 2020 Australia fires reduced the global temperature by approximately one-tenth of a degree Fahrenheit-which is important for every tenth of a degree in the fight against climate change.
In order to refine and calibrate computer models of wildfires and climate, we are studying multiple scales of thermocumulonimbus clouds from British Columbia and Australian fires, from molecules in fiery gas, to how flames move in specific landscapes, and how smoke moves in the atmosphere. In the evolution, the last is how the smoke spreads around the glove. Our work also includes laboratory experiments and field observations of smoke collected by our Aerosol Gas Forensic Experiment Center (CAFÉ), where we study black carbon emissions and their mixing with organic gases in fires.
We use this data to verify and improve our computer models, called HIGRAD and FIRETEC. Together, these computer tools help us study how fire moves in the landscape and interacts with the atmosphere. Then we incorporated the results into the global climate model.
Through this multi-scale, interdisciplinary approach, we are able to simulate the evolution of all gases and particles produced by fires, from their burning as wood, forest waste and other fuels to their being trapped as particles or droplets (aerosols). The final destiny in the cloud and was taken to a distant place. Understanding the evolution of these particles is the key to understanding the origin, life cycle and impact of the cumulonimbus.
Our work is still in progress, but so far, we have seen that, in addition to the smoke, gas and particles produced by the 2017 BC fire, the condensation of water and ice on the particles releases latent heat to provide energy for this lofting , So that the plume height increased by about 3 miles to penetrate the stratosphere. Less than half of the mass of smoke comes from particles released by the fire itself. The rest is formed by the condensation of organic vapor in the cold coke updraft, which is a surprising result.
Mixed influence on climate
Global climate models allow us to study the consequences of this huge smog injection event on a larger scale. In our simulation, the sun heated the black carbon in the smoke. In the stratosphere, solar heating increases the temperature of the atmosphere, which is different from the troposphere where we live, where the air gets colder as the altitude increases. This leads to more active weather in the troposphere and slower weather in the stratosphere. Therefore, the smog in the stratosphere can last for months to years, and the smog in the troposphere will disappear within a week.
In addition, the soot in the smoke absorbs sunlight to heat the air, causing it to rise further (Marlon effect). Our simulation shows that the height of the smoke exceeds 12 miles, which is consistent with satellite observations. The smoke remained in the atmosphere for about five months before it settled, which has also been confirmed by observations. The relatively short time in the stratosphere limits the long-term climate impact of fire smoke in British Columbia, but the regional short-term impact on air quality is significant.In addition, soot deposited on snow, oceans and other surfaces may cause warming and melting
We have also begun to model the larger and longer-lived fire in New South Wales, Australia in 2019-2020. They injected four times as much smoke into the stratosphere as fires in British Columbia. Our preliminary analysis shows that this smog is caused by the same cumulonimbus cloud mechanism and large-scale uplift in the western Pacific. Solar heating adds more energy and brings smoke to more than 15 miles. It stayed at high altitude for a year and a half.
Our model has not yet produced a clear prediction of the global cooling effect of large amounts of soot and aerosol injected into the stratosphere or the long-term climate heating effect of gas. There is more work to be done there. However, one thing is clear: in these days of climate change, increased drought and overgrowth of forests, extreme fires have become a reality. Fire Cumulonimbus will continue to affect the behavior of fires on the ground and the weather above and elsewhere. The more we know, the better we are able to meet the challenges they pose.
This is an opinion and analysis article; the views expressed by the author or author are not necessarily Scientific american