Australia's wildfires have been catastrophic this year. They raged for weeks, claimed lives, killed at least a billion different animals, and caused colossal damage. An area the size of the Netherlands is estimated to have completely burned out. The reasons for the devastating fires are described here.
Now let's talk about how forest fires create their own weather systems and thus generate themselves. First and foremost, the massive fire is a huge source of heat. The temperature in the fire zone can reach 1200 degrees Celsius.
The hot air expands and therefore the air pressure drops. The result is a mesocyclone - a small area of low pressure. Similar areas of low pressure occurred in the forest fires in the hot summer of 2010 in Central Russia.
The second important effect is powerful convection. Hot air has a lower density. This forces him to rapidly rise above the forest fire.
But we know that any system strives for balance. The air mass deficit above the fire site is compensated by the overflow of colder and denser air from the surrounding areas. The wind acts as a transporter. Due to the huge temperature difference, the wind becomes stormy. In some cases, its speed can reach 28 m / s (100 km / h).
A closed cycle arises. A strong wind further fanned the flames and spreads the fire to neighboring territories. Thus, the "firestorm" begins to support itself.
As the air rises, the floating air cools and its relative humidity increases.
At some point, it condenses into clouds and precipitation. Extremely high temperatures can cause a cumulus cloud to develop to high altitudes. This is how pyrocumulative clouds arise - thunderclouds caused by forest fires.
Someone will say: “Thunderclouds, great! A downpour will put out the fire. " But the problem is that the lower boundary of the pyrocumulative cloud is located very high - at a distance of several kilometers. Due to the heat and dryness in the fire zone, precipitation from it will evaporate before reaching the ground.
The heat expended in evaporation will lower the air temperature. Having become denser, which means - heavy, he rushes down. Colliding with the ground, a strong downdraft of cold air swirls into a squall gate. This is how a destructive flurry arises.
Thus, instead of extinguishing the fire with rain, the precipitation further fan the fire with a strong wind. This phenomenon is called "dry" thunderstorms. And don't forget about lightning! They are able to ignite a new fire.
So, we looked at the mechanism of how large forest fires shape their own weather, sometimes even "dry" thunderstorms, which can exacerbate the situation. Stopping a firestorm is not easy. To do this, there are only two ways: to deprive it of combustible material (for example, by controlled oncoming fire) or to wait for a large-scale weather change.
Pyrocumulative clouds can also be seen over the vent of erupting volcanoes and over violent city fires.