Dec 29, 2019 06:00 PM
https://eos.org/articles/what-do-you-get...a-wildfire
INTRO: There are few things more ominous than a looming thundercloud. Add a wildfire to the mix, and the result can be a towering tempest of thick smoke, smoldering embers, and superheated air. Fire-fueled thunderstorms are naturally occurring weather systems that sometimes spin up as a result of smoke and heat billowing from intense wildfires. These extreme storms, called pyrocumulonimbus (pyroCb), occur infrequently, but when they do they can lead to tragic results.
Wildfires give off intense heat, forcing large amounts of smoke and hot air to rise. As the mixture moves higher into the troposphere—the lowest layer of Earth’s atmosphere—it cools and expands as the air pressure drops. Moisture in the air soon condenses, forming big puffy clouds called pyrocumulus clouds.
When conditions in the atmosphere are just right—including a hot, dry layer of air near the ground and a cooler, wetter layer above it—the atmosphere can become convectively unstable. Increasingly turbulent air sets water droplets and ice crystals in pyrocumulus clouds on a collision course, building up an electrical charge and turning the system into a towering thunderhead.
The soaring pyroCbs, which rarely produce rain on the ground even though they are thunderstorms, can even rise out of the troposphere and extend into the stratosphere tens of kilometers above the surface. Not surprisingly, pyroCbs can be incredibly dangerous.
On 7 February 2009, the most devastating day of fires in Australia’s history spawned at least three pyroCbs that carried embers 30 kilometers from their source and sparked lightning that ignited additional fires 100 kilometers away. Known as the Black Saturday bushfires, these fires collectively burned 4,500 square kilometers and claimed 173 lives.
A pyroCb that formed during the Carr Fire near Redding, Calif., in 2018 had such strong winds that it created a tornado-strength fire vortex, and a pyroCb in Canberra, Australia, in 2003 was so extreme that it released a torrent of black hail and turned the daytime sky as dark as night... (MORE)
INTRO: There are few things more ominous than a looming thundercloud. Add a wildfire to the mix, and the result can be a towering tempest of thick smoke, smoldering embers, and superheated air. Fire-fueled thunderstorms are naturally occurring weather systems that sometimes spin up as a result of smoke and heat billowing from intense wildfires. These extreme storms, called pyrocumulonimbus (pyroCb), occur infrequently, but when they do they can lead to tragic results.
Wildfires give off intense heat, forcing large amounts of smoke and hot air to rise. As the mixture moves higher into the troposphere—the lowest layer of Earth’s atmosphere—it cools and expands as the air pressure drops. Moisture in the air soon condenses, forming big puffy clouds called pyrocumulus clouds.
When conditions in the atmosphere are just right—including a hot, dry layer of air near the ground and a cooler, wetter layer above it—the atmosphere can become convectively unstable. Increasingly turbulent air sets water droplets and ice crystals in pyrocumulus clouds on a collision course, building up an electrical charge and turning the system into a towering thunderhead.
The soaring pyroCbs, which rarely produce rain on the ground even though they are thunderstorms, can even rise out of the troposphere and extend into the stratosphere tens of kilometers above the surface. Not surprisingly, pyroCbs can be incredibly dangerous.
On 7 February 2009, the most devastating day of fires in Australia’s history spawned at least three pyroCbs that carried embers 30 kilometers from their source and sparked lightning that ignited additional fires 100 kilometers away. Known as the Black Saturday bushfires, these fires collectively burned 4,500 square kilometers and claimed 173 lives.
A pyroCb that formed during the Carr Fire near Redding, Calif., in 2018 had such strong winds that it created a tornado-strength fire vortex, and a pyroCb in Canberra, Australia, in 2003 was so extreme that it released a torrent of black hail and turned the daytime sky as dark as night... (MORE)