Firestorms

Firestorms have arisen from the merger of fires from multiple simultaneous ignitions in a heavily fuel-laden urban environment. Within an hour surface-level radial inflow from all directions sustains a large-diameter convective column typically, the firestorm reaches peak intensity in a couple of hours, with inflow speeds inferred to attain 25-50 ms and with the plume reaching 10 km e.g., Hamburg, Dresden, Hiroshima. Winds associated with the nonpropagating holocaust relax to ambient in six-to-nine hours, with often 12 km to the 2nd power reduced to ashes. Here the firestorm is interpreted to be a mesocyclone rotating severe local storm, with exothermicity from combustion rather than condensation of water vapor supporting convectively induced advection. The rapid swirling of the surrounding air results in reduction of entrainment into the plume, such that the mass flux ascending in the buoyant plume is furnished entirely by a near-ground layer with large radial inflow. Integral treatment of a convective column over a maintained heat source in the absence of a cross-wind is generalized to include 1 reduction of entrainment with swirling 2 stratification of the ambient that varies with altitude and 3 time evolution based on spin-up under conservation of angular momentum, incorporating large radial pressure gradient. Only exceedingly large heat release rate sustained over a concentrated area, in the presence of a very nearly mechanically unstable atmospheric stratification, is consistent with onset of vigorous swirling on the scale of two hours.