Today’s Wonder of the Day was inspired by Rabdi. Rabdi Wonders, “How are pyrocumulus (fire) clouds created?” Thanks for WONDERing with us, Rabdi!
If you live in the western part of the United States, thunderstorms can be a mixed blessing. The rain they bring can be a welcome respite from dry conditions. However, if storms bring lightning and not much rain, they can spark new wildfires in tinder-dry forests.
If you've ever been near a wildfire or seen pictures of one on the news, you may have noticed another interesting weather phenomenon that often accompanies a widespread fire. If you look up at the sky above the smoke from the fire, you might see a towering cloud shaped like cauliflower or a mushroom.
Scientists call these unique clouds pyrocumulus clouds or "fire clouds." Regular cumulus clouds form when heat from the ground warmed by the Sun rises high into the air, where it cools and causes water vapor to condense. Pyrocumulus clouds are similar, except the heat comes from another source.
In the case of pyrocumulus clouds that form over a wildfire, the source is clear: the heat comes from the wildfire. Pyrocumulus clouds can also form over other intense heat sources, such as volcanic eruptions or nuclear explosions.
The intense heat from these events causes air masses to rise rapidly. This gives pyrocumulus clouds their towering stature. Usually found between 2,000 to 30,000 feet in elevation, pyrocumulus clouds can often be seen for miles.
Their large size also stems from the increased amount of moisture in the air caused by the evaporation of water inside burning plant life. When that moisture cools, it condenses more quickly because of all the smoke and ash particles in the air as a result of the fire, eruption, or explosion.
Scientists keep a close eye on pyrocumulus clouds. Since they can reach extreme heights, they can spread smoke, ash, and other pollutants high into the atmosphere where winds can disperse them over a wide area. This is why wildfires, volcanic eruptions, and nuclear explosions can affect air quality for many miles in every direction.
Pyrocumulus clouds can also have different effects on fires below them. Occasionally the moisture within them will fall as rain, possibly extinguishing the fire that created them.
At other times, especially if there's a lot of moisture in the air, pyrocumulus clouds can grow into pyrocumulonimbus clouds, which is a type of thundercloud. Pyrocumulonimbus clouds can produce lightning that, in turn, can cause more fires.