NASA details wildfire storm encounter during INSPYRE research flights

NASA said on October 2 that researchers on its INSPYRE campaign spent three hours sampling a smoke plume after a wildfire generated a thunderstorm-like cloud over the Wildhorse grass fire in eastern Idaho on August 26. The encounter gave scientists a close view of fire-driven weather that can endanger crews and carry smoke high into the atmosphere, although the measurements have yet to yield final findings.

The cloud was a pyrocumulonimbus, or pyroCb: a cloud produced when an intense fire drives a powerful column of heated air upward. NASA says such clouds can bring lightning, rain and strong winds. The largest can lift smoke 10 to 15 kilometers, or 30,000 to 50,000 feet, above the ground, sometimes reaching the stratosphere. What happens to that smoke matters well beyond the fire that produced it.

How the Wildhorse fire gave researchers a rare encounter

NASA’s Gulfstream research aircraft was returning from a fire farther west when the team learned that the Wildhorse grass fire had become unexpectedly intense. Sarah Woods, a National Center for Atmospheric Research scientist serving as a spotter, saw the fresh remains of a pyroCb near the fire. NASA says the crew identified it as fire-generated after seeing the fire below the cloud.

At Woods’ request, the pilots turned back. For roughly three hours, the aircraft flew through the cloud plume and smoke drifting northwest toward Wyoming. NASA says it gathered measurements about an hour after the cloud erupted. The account describes an unexpected opportunity to observe a phenomenon the team had spent weeks trying to find; it does not present a completed analysis of the Wildhorse plume.

What NASA’s INSPYRE aircraft measured

INSPYRE stands for INjected Smoke and PYRocumulonimbus Experiment. NASA calls it the first aircraft campaign designed specifically around studying pyroCbs. Its campaign archive gives field dates of July 15 through September 8 across the western United States and Canada. The project brought together researchers studying the fires, clouds, smoke and conditions above them.

For six weeks, researchers aboard a Gulfstream based near Boulder, Colorado, collected smoke particles and gases, photographed ice crystals, and measured radiation passing through clouds and reflected into space. They flew above, below and through wildfire clouds. A NASA ER-2 aircraft carrying 14 instruments observed fire intensity, updraft speeds, smoke and cloud properties from above, while sensor-equipped trucks made observations from the ground.

NASA says other coordinated Gulfstream and ER-2 flights observed active fire-driven airflow. Researchers intend to combine aircraft measurements with satellite and ground observations, then compare them with models to investigate how smoke plumes develop over subsequent days and weeks. Those comparisons are the next stage of the work, rather than a result already demonstrated by the Wildhorse encounter.

Why wildfire storms matter to fire crews and forecasts

The immediate concern for firefighters is that a fire-generated cloud can change conditions around the flames. Neil Lareau, a University of Nevada, Reno atmospheric scientist who led INSPYRE’s ground observations, told NASA that a fire can make its own thunderstorm and, in the process, its own wind. He hopes better understanding could eventually support warnings about dangerous downdrafts and wind shifts, giving managers time to move crews.

In an August interview with Weather.com, INSPYRE investigator Dave Peterson described fire-generated storms as poorly understood and poorly forecast. He said that gap can complicate firefighting, and that the storms can produce erratic winds and lightning and may ignite fires downwind. Peterson also identified potential benefits for public resilience and evacuation efforts. Those are reasons to study the storms, not evidence that a new warning system is ready.

Smoke is the longer-range question. NASA says pyroCb smoke reaching the stratosphere can travel across continents or around the globe and remain aloft longer than smoke in the lower atmosphere. Particles there can affect how much solar energy the atmosphere absorbs and how much reaches Earth’s surface. Peterson told NASA that most numerical prediction models do not explicitly include the effects of pyroCb smoke injections.

Olga Kalashnikova, a NASA Jet Propulsion Laboratory researcher and INSPYRE principal investigator, told NASA that scientists still do not understand how much pyroCb formation depends on fire energy, fire intensity or atmospheric conditions above a fire. The campaign’s measurements may help separate those influences and show how clouds alter smoke chemistry. NASA’s October account leaves open how much of the Wildhorse plume reached the stratosphere and whether the campaign will produce operational forecasting improvements.