NRL Scientists Study PyroCb Environmental Effects

WASHINGTON  –   WASHINGTON — Naval Research Laboratory Remote Sensing Division scientists continue to study the data pyrocumulonimbus (pyroCb) plumes generated during brush fires that ravaged southeastern Australia between Dec. 29, 2019 and Jan. 4, 2020.

Researchers used the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite that provides insight into the role clouds and airborne particles play in regulating Earth's weather, climate, and air quality.

PyroCbs are fire-induced thunderclouds that inject massive amounts of smoke particles into the upper atmosphere. When these events are hot enough, wildfires can trigger convective updrafts, the depths of which extend well into the lower stratosphere. The lower boundary of the stratosphere can be as high as 13 miles.

During the Australian pyroCb event, fires emitted an unprecedented amount of smoke to heights over 10 miles. One plume, estimated at 3-miles thick and 621 miles across - about the distance from Atlanta to Washington D.C. - traveled east to South America by late January. Over several weeks, the smoke plumes dissipated and covered the Southern Hemisphere, circumnavigating the globe.

This event also showed the first evidence of smoke causing changes to winds in the stratosphere. Researchers published their report, “Australian PyroCb Smoke Generates Synoptic‐Scale Stratospheric Anticyclones,” in Geophysical Research Letters May 30.

“The stratosphere has traditionally been described as an impenetrable barrier to tropospheric aerosol, with the exception of volcanoes,” said George “Pat” Kablick III, an NRL atmospheric scientist. “This event showed for the first time that pyroCb plumes can cause rotation generated by solar heating of the smoke. We need to study how these pyroCb events change stratospheric composition and meteorology because it may have effects on stratospheric radiation budgets and the ozone layer.”

PyroCbs were discovered at NRL about 20 years ago by one of the study’s coauthors, Mike Fromm. NRL scientists in Washington and in Monterey, California, continue to analyze and explain what is happening in real-time when a pyroCb occurs - especially how these events could affect naval operations.

“The battle space environment is something the Navy has a deep understanding of,” said Kablick, who started studying pyroCb plumes in 2011. “But this understanding can always be improved, and the new pyroCb phenomenon we described in our paper is one of those improvements.”

While research and analysis continue, many compare the plumes to a hypothesized nuclear winter. While the comparisons are valid in how plume behaviors are compared, Kablick said caution must be taken.

“The nuclear winter studies assume that firestorms generated by nuclear weapons occur in large urban cities,” said Kablick. “This may have vastly different fuel-types, smoke properties, and burning conditions than the wild land fire conditions typical for pyroCbs.”

More than seven months after the initial brush fires, Kablick said, remnants of the plumes are still detectable, even at altitudes above 18 miles.

“While they are no longer the tightly-concentrated aerosol plumes they once were, certain satellite instruments can still detect faint signals,” said Kablick. “However, they are more dispersed, and the rotation and self-lofting have probably ceased.”

This type of research is just beginning said Kablick, and these events open up a whole new vein of scientific research. “So keep an eye out for future discoveries. There is a lot to learn.”

The Remote Sensing Division conducts basic research, science, and applications aimed at the development of new concepts for sensors and imaging systems for objects and targets on Earth, in the near-Earth environment, and in deep space.


About the U.S. Naval Research Laboratory

NRL is a scientific and engineering command dedicated to research that drives innovative advances for the Navy and Marine Corps from the seafloor to space and in the information domain. NRL is located in Washington, D.C., with major field sites in Stennis Space Center, Mississippi; Key West, Florida; and Monterey, California, and employs approximately 2,500 civilian scientists, engineers and support personnel.