Actually, I think they only simulate the fires, and therefore soot production, for 40 min. So you may well have a good point. I do not know whether it would be a difference by a factor of 10. Figure 6 of Reisner 2018 may be helpful to figure that out, as it contains soot concentration as a function of height after 20 and 40 min of simulation. Do the green and orange curves look like they are closely approaching stationary state?
Wow—only 40 minutes—my understanding is actual firestorms take hours. This graph is for the low loading case, which did not produce a firestorm. The lines do look similar for 20 and 40 minutes, but I don’t think it’s the case we are interested in. They claim only the fine material that burns rapidly contributes, but I just don’t think that is the case with actual firestorms. The 2018 was with low loading, and most of the soot is in the lower troposphere (at least after 40 minutes), so the question is when they actually did find a firestorm, what is the vertical soot distribution? For Livermore, it was mostly upper troposphere. Los Alamos did recognize that they were not doing latent heat release even in the 2019 simulation. I think this is quite important, because it’s the reason that thunderstorms go to the upper troposphere (and sometimes even stratosphere). It’s been a while since I took geophysical fluid dynamics, but the argument that the initial plume would stabilize the atmosphere seems off to me. If we look at the example of night in the atmospheric boundary layer (lower ~1 km), the surface cools radiatively, so you get stratification (stable). But when the sun comes up, it warms the surface of the earth, and you get thermals, and this upward convection actually destabilizes the boundary layer. Now it is true if you have a fire in a room that the hot gases can go to the ceiling and stabilize the air in the room. But if they are arguing that the plume only goes up a few kilometers (at least for the non-firestorm case), it seems like in those few kilometers, the potential temperature would be more equalized, so overall less stability. Even if that’s not the case, the plume has hardly even reached the upper troposphere, so there would be hardly any change in stability there. In addition, if the simulation is run over hours, then new atmosphere could come into place that has the same old stability. So I think the Livermore results are more reasonable.
Wow—only 40 minutes—my understanding is actual firestorms take hours. This graph is for the low loading case, which did not produce a firestorm. The lines do look similar for 20 and 40 minutes, but I don’t think it’s the case we are interested in. They claim only the fine material that burns rapidly contributes, but I just don’t think that is the case with actual firestorms. The 2018 was with low loading, and most of the soot is in the lower troposphere (at least after 40 minutes), so the question is when they actually did find a firestorm, what is the vertical soot distribution? For Livermore, it was mostly upper troposphere. Los Alamos did recognize that they were not doing latent heat release even in the 2019 simulation. I think this is quite important, because it’s the reason that thunderstorms go to the upper troposphere (and sometimes even stratosphere). It’s been a while since I took geophysical fluid dynamics, but the argument that the initial plume would stabilize the atmosphere seems off to me. If we look at the example of night in the atmospheric boundary layer (lower ~1 km), the surface cools radiatively, so you get stratification (stable). But when the sun comes up, it warms the surface of the earth, and you get thermals, and this upward convection actually destabilizes the boundary layer. Now it is true if you have a fire in a room that the hot gases can go to the ceiling and stabilize the air in the room. But if they are arguing that the plume only goes up a few kilometers (at least for the non-firestorm case), it seems like in those few kilometers, the potential temperature would be more equalized, so overall less stability. Even if that’s not the case, the plume has hardly even reached the upper troposphere, so there would be hardly any change in stability there. In addition, if the simulation is run over hours, then new atmosphere could come into place that has the same old stability. So I think the Livermore results are more reasonable.