Scientists have long known that volcanoes can launch large amounts of particles into the stratosphere. In recent decades, it has become clear that wildfires also do this by generating towering, smoky pyrocumulonimbus (pyroCb) clouds.
The largest pyroCbs are impressive weather features that generate enormous storm clouds capable of unleashing lightning, hail, and heavy rain. A growing body of research shows that pyroCbs can also leave a large footprint in the upper atmosphere by channeling pulses of particles and gases into the mostly dry, cloudless reaches of the stratosphere. Once there, the smoke can spread widely and linger for months or years, sometimes circling the globe and likely influencing the ozone layer and the Earth’s energy budget.
Understanding these enigmatic and dangerous clouds is why a team of atmospheric scientists, part of a NASA mission called INSPYRE (Injected Smoke and PYRocumulonimbus Experiment), is spending the summer chasing them with NASA’s ER-2 aircraft, the NSF/NCAR GV, and a suite of truck-mounted sensors. The team completed one of its first tests of the summer on August 3, 2026, when the GV flew through a high-altitude pulse of smoke from the Widemouth 2 fire, one of the largest in Utah so far this year.
Lightning ignited the fire on July 27, 2026, but it remained relatively small until August 2, when it doubled in size amid intense winds and hot, dry conditions. That afternoon, shortly after producing two bursts of pyroCb, the MODIS (Moderate Resolution Imaging Spectroradiometer) on NASA’s Aqua satellite captured this image (above), showing a high-altitude chimney of clouds and smoke casting a shadow on the low-altitude smoke below.
These explosions propelled the clouds high enough that Aqua measured cloud-top brightness temperatures well below -40°C, a common threshold for identifying pyroCbs and a sign that cloud tops were bubbling to the top of the troposphere and sometimes into the stratosphere. The glow temperature measurements “reveal two discrete pulses of pyroCb action,” said Michael Fromm, a scientist at the US Naval Research Laboratory. “The westernmost pulse is the youngest and stands out in the visible images for its shadow.”
Although relatively routine and minor, this pyroCb event followed a predawn pyroCb from the same fire, imaged by NOAA’s GOES-West weather satellite. “Morning pyroCbs are much more unusual,” Fromm said, because they don’t benefit from the daytime heating that helps fuel convection. In this case, however, there appeared to be enough atmospheric instability and water vapor in the air to allow the development of pyroCb.
Multiple pyroCb in a single day could have added unwanted complexity for meteorologists and firefighters fighting the fire and organizing evacuations, said David Peterson, INSPYRE principal investigator. “Minimizing that kind of uncertainty for fire forecasters is a big part of the reason we’re here studying this,” he added.
Remote sensing experts like Peterson and Fromm routinely study pyroCbs from afar with satellites, but it’s less common for pilots to chase and sample smoke plumes just hours after they form. In this case, the GV plane, which was grounded in Colorado when the Widemouth 2 fire broke out, headed directly into a high-altitude plume of smoke while hovering over New Mexico on August 3. The plane’s instruments sampled smoke about 12 kilometers (8 miles) above the surface, collecting data at an altitude not normally incorporated into forecast models.
During that mission, a scientist on board captured this image (above) of a pyrocumulus (pyroCu) billowing over the Widemouth 2 fire. While not as tall or energetic as pyroCbs, pyroCus are precursor clouds that share many of the same characteristics. Here, heat from the fire is fueling strong convective updrafts, forming a towering cloud with puffy tops that tower over the upper troposphere as lower-altitude smoke floats downward.
Satellites excel at identifying pyroCbs by measuring the temperature of the cloud tops that form above the smoke columns. Using this technique, researchers have established that wildfires produce around 70 pyroCbs per year, many of them in dense forests in Canada and Russia, although many also occur in grasslands and savannahs in the United States and Australia. So far in 2026, Fromm and his colleagues have identified at least 13 in the continental United States.
Since one of the first pyroCbs appeared in scientific literature in the early 2000s, scientists have cataloged more than 700 events and now believe wildfires may contribute up to 25 percent. of black carbon and organic aerosols in the lower stratosphere. The high frequency of pyroCbs means that the total mass of particles they inject over the course of a wildfire season can rival that of large volcanic eruptions.
Still, many questions about the enigmatic clouds remain unanswered. It is unclear what vegetation is most likely to fuel pyroCb, why some generate more lightning strikes than others, why they form in only a small fraction of fires, and how to accurately forecast them.
“Whether it’s their dangerous manifestations on Earth or their lasting footprint in the upper troposphere and lower stratosphere,” Fromm said, “pyroCbs continue to surprise us.”
NASA Earth Observatory images by Michala Garrison, using MODIS data from NASA EOSDIS LANCE and GIBS/Worldview. Photo by Bernadett Weinzierl/University of Vienna. Story by Adam Voiland.
August 2, 2026: natural color
August 2, 2026: Brightness temperature
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