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Mesocyclones form when air rises and rotates in a "pillar" of sorts. It's sometimes associated with thunderclouds and tornado formation.

A certain kind of cumulonimbus, the cumulonimbus flammagenitus, can form above a firestorm of sufficient strength (magnitude, temperature, whatever the thing being measured is). Some cumulonimbus flammagenitus clouds have generated true fire tornados (as opposed to the fire whirl, which is commonly called a fire tornado) indicating that these clouds do form mesocyclones.

My question is, could a firestorm generate a hurricane-like cyclone, with strong surface winds along a large area, raining ash and embers? If so, would it move or be stationary? How long could it sustain itself? What would be involved in its formation?

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I don't think so. A large fire could generate a circulation with strong low-level convergence and upper level divergence that would cause subsidence as the air radiatively cooled. If the fire were stationary and huge, the Coriolis effect could make it's upper level outflow turn, but I don't think an intense hurricane-like cyclone could form unless the fire were actually relatively small (like the eyewall of a hurricane), but in that case I'm not sure that the necessary pressure gradient could be maintained (even if the fire could somehow continue to be fueled).

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    $\begingroup$ The spin of a tropical cyclone does not come from converting planetary angular momentum as the storm moves poleward. It instead comes from air flowing inward toward the low pressure at the center of the storm over a vast area. The Coriolis effect turns the airflow turns to the right in the northern hemisphere / to the left in the southern hemisphere. This rather than poleward motion is the source of a tropical cyclone's primary circulation. Cyclones can strengthen as they move toward the equator. What's needed is an energy source to sustain the primary circulation, such as warm ocean water. $\endgroup$ – David Hammen Sep 16 '17 at 11:39
  • $\begingroup$ I was sort of sloppy with my language, as the hypothetical situation being described didn't need a super pedantic answer. The hypothetical firestorm, for instance, probably isn't occurring over the tropical ocean. In any case, I edited my comment. Note that angular momentum (M) for a tropical cyclone can be written as M = r v + (1/2) f r^2, so Coriolis (f) is part of the M budget. Anthes (1974) shows that the Coriolis torque is a rather small part of the total angular momentum budget, but the north-south asymmetry of large storms may provide some of the needed angular momentum import. $\endgroup$ – brian Sep 16 '17 at 19:03

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