This is the sound of thunder and a steady rain hitting against the concrete. The rolling and gradually dissipating rumble of thunder is caused by the time delay of sound coming from different portions of a long stroke of lightning. Because the electrostatic discharge of terrestrial lightning superheats the air to plasma temperatures along the length of the discharge channel in a short duration, kinetic theory dictates gaseous molecules undergo a rapid increase in pressure and thus expand outward from the lightning creating a shock wave audible as thunder. Since the sound waves propagate not from a single point source but along the length of the lightning's path, the sound origin's varying distances from the observer can generate a rolling or rumbling effect.
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