Weather generated by wildfires
A large number of wildfires occur every year in forests and grasslands distributed around the world, swallowing precious forest and grassland resources and causing huge losses to the lives and property of surrounding residents. As climate changes, global temperatures continue to rise, and wildfires are also increasing in intensity and scope. In July this year, a study published in the British journal Nature Ecology and Evolution showed that the frequency and intensity of extreme wildfires around the world have roughly doubled in the past 20 years.
This result has attracted widespread attention. On the one hand, wildfires can cause disasters, and during the burning process, they will further increase carbon emissions and intensify climate change, constituting negative effects of mutual influence. On the other hand, in addition to causing disasters and affecting the climate, wildfires occurring at the bottom of the atmosphere can also have a direct impact on the weather system, especially when the scope of wildfires is large enough to create a local weather system around wildfires. This is not difficult to understand. When forest and grass are burned, a large amount of heat will be released and the air near the ground will be heated. The density of the heated atmosphere is lower than that of the relatively low temperature air in the surrounding range, making the heated air mass rise like a hot air balloon. After the hot air rises, the surrounding air will flow into the space vacated and continue to heat above the wildfire, thereby creating a circulating convective system in which cold and warm air continues to move in horizontal and vertical directions.
Such a brief analysis is not complex in the logical relationship and can be reasonably explained by the vertical unstable structure problem in the weather system. However, in the actual atmosphere, what kind of weather process or what kind of impact and consequences the maintenance of this thermal convective system will be accompanied by depends on the initial state of the atmosphere and surrounding environmental conditions, and has certain complexity. Recently, meteorologist Kyle Hillburn of Colorado State University conducted a detailed analysis of the consequences of wildfire weather under different conditions.
Whether the warm air in wildfire areas can continue to rise is closely related to the surrounding atmospheric environment. If the ambient temperature drops rapidly with altitude, the rising air mass will continue to remain warmer than the environment, helping to maintain the rise. If the warm air mass rises high enough, the water in it will condense, forming pyrocumulus clouds. If the air continues to rise to freezing heights, the clouds will contain both water droplets and ice crystals. Collisions between these different particles will cause the separation of charges. If the electric field generated by the accumulation of different charges is large enough, lightning will occur, neutralizing these charges. It can be seen that the scope and intensity of wildfires, the surrounding vertical stratification conditions, and the moisture contained in the atmosphere constitute factors that influence the development of wildfire weather systems. Different conditions will lead to differences in the development of the system.
Another type of weather system caused by wildfires is Fire Whirls, which produce swirling currents similar to tornadoes when surrounding air moves towards the area of updraft caused by wildfires. If the surrounding atmospheric conditions are favorable enough, if there is obvious wind shear, the wind speed around the fire vortex will be strengthened, sometimes very violent, and burning branches and leaves will fall to the surrounding area with the changeable wind, causing a wider range of wildfires. Such fire vortices with changeable wind directions and fierce wind speeds are difficult to prevent and have strong uncertainties in time and space. People involved in fire fighting and disaster relief should pay special attention.
The weather system generated by wildfires, like common convective weather, is also accompanied by downdrafts in different regions and times. This downdraft can be strong, adding to the complexity of the atmospheric flow around wildfires. The changeable wind direction makes the fire difficult to predict, making it more difficult to extinguish the fire.
With the development of high-resolution meteorological satellites, meteorological experts have been able to analyze the occurrence of wildfire weather through satellite data. They believe that this is not a rare weather phenomenon and is quite universal. They can also carry out monitoring and early warning to prevent wildfire disasters. Provide guidance. The impacts of climate change are multi-faceted, and the increase in wildfires is one of them. In addition to paying attention to the laws of its long-term evolution, research on specific impacts and regional or local change characteristics should also be strengthened, not only from the perspective of scientific theory. Deepen understanding and solve specific problems in reality from the perspective of disaster prevention.
