Thunder can be defined as the acoustic emission associated with a lightning discharge" [2].
Thunder
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A short sample of a crack of thunder
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Types[edit]
All processes in CG and IC discharges produce thunder which can be divided into 2 categories:
audible (frequencies greater than 20Hz) which come from a series of decaying shockwaves produced by the expansion of various portions of the nearly instantaneous heated lightning channel which is filled with ionized air molecules (plasma). Of these there are: a) rumbling thunder which is a long low series of growling-like sounds and b) clapping thunder that is usually loud and quick.
non-audible or infrasonic thunder (frequencies lower than 20 Hz) which is thought to originate from ICs where large volumes of air are displaced by the rapid removal of electrons or protons from the cloud itself. This category of thunder has only recently received the attention of the scientific community.