Dynamics of the Thermal Uplifting in the Atmosphere Under a Continuous Supply of Heat: Practical Application Examples
Keywords:thermal, temporal dependence, speed of motion, thermal upper boundary, excess temperature, generation of acoustic and atmospheric gravity waves, ecological consequences of fires
The author has earlier considered the dynamics of an isolated thermic arising from an instant heat release. The rigorous analytical, as well as simplified, solutions describing the dynamics of the uplifting of a spherical thermic have been obtained. Such a thermic appears during a short-term release of heat, e.g., during an explosion. The uplifting of a meteoroid thermic has also been studied. The theory of the thermic has found applications in the magnetic precursors of earthquakes. At the same time, the heat can be supplied during many hours or even days when big forest fires occur, peat fires burn, volcano eruptions occur for a long time, and during the release of heat before earthquakes. The dynamics of the uplifting of a thermal under these circumstances is considerably different from an instantaneous energy release. Employing the cylindrical model of a thermic, the dynamics of the thermic has been studied in the case of the continuous supply of heat. Within the model, the analytical solutions to the set of equations governing the temporal dependences of the velocity of a parcel of the heated air and the position of the upper bound of the thermic, as well as the excess temperature in the heated parcel have been obtained. The upper thermal boundary speed and location has been shown to increase with uplifting, while the excess temperature to gradually decrease. The numerical estimation has been performed for characteristic situations. The ecological consequences of large-scale fires, as well as the mechanisms for generating gravity waves by the thermals, are discussed. The physics-based mechanisms for generating acoustic wide-band emissions by the thermals have been analyzed; the wave periods have been estimated to be 1–103 s. The energy of acoustic emissions from a big fire has been estimated to be approximately 1014 J. At the same time, the energy of acoustic emissions from all fires that occurred in the Russian Federation in 2020 amounts to 7∙1016 J, while in Ukraine it is three orders of magnitude lower.
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