![]() Effect of tortuosity on rumbling or clapping thunder The different sizes of tortuous segments in a lightning rod. This type of discharge is commonly called artificially triggered lightning, and was used, among others, by Depasse in 1986, 19 at Saint-Privat D'Allier, France, where the pressure profile behind a lighting-generated shockwave was matched to the theoretical profile obtained from cylindrical shockwave theory developped by Few in 1969. This "forces" an electrical current from the electrically-charged thundercloud to the ground via the attached electrical wire. The most common way of artificially generating lightning is with a rocket, that is connected to a steel wire and fired into a thundercloud to create a short circuit near ground. This is because of the impossibility to predict exactly where lightning will strike and thus to place a microphone near it. Most studies that were done on thunder could not analyze from close range a naturally produced sound. ![]() It is in this last section of the shock wave that the thunder is heard. It has been empirically found that the loudest frequency in thunder is:į m a x = c 0 ( p 0 E 0 ) 1 2 is the total energy released by the spherical shock wave. The frequency spectrum of thunder (and unfiltered rain sounds) obtained using Audacity 1.3 (Beta). This category of thunder has only recently received the attention of the scientific community. 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.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. audible (frequencies greater than 20 Hz) 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).Problems listening to this file? See media help.Īll processes in CG and IC discharges produce thunder which can be divided into 2 categories: "Thunder can be defined as the acoustic emission associated with a lightning discharge". The three main modes of charge transfer to ground (adapted from Lightning: Physics and Effects (2003)). Malan who first studied these processes in the 1930s) which are transient processes during a continuing current (2nd mode).įigure 3. Continuing currents (that last for hundreds of milliseconds) which are long quasi-stationary arcs.The charges have three main modes in which they can be sent to the ground from the cloud (see diagram): ![]() The CGs can be categorized into 4 groups: (a) downward negative (90% of all CGs are of this group), (b) upward positive, (c) downward positive, and (d) upward negative. There are two main types of lightning discharges: cloud-to-ground (CG) and intra-cloud (IC), the latter accounting for about 3/4 of all discharges (there are however other types of discharges that are less commonly encountered such as ball lightning). The 4 groups of cloud-to-ground (CG) discharges (adapted from Lightning: Physics and Effects (2003)). 2.3.2 Effect of tortuosity on rumbling or clapping thunder.2.3.1 Assuming perfectly cylindrical/spherical expansion. ![]() The air molecules within ionize to generate a highly powerful shock wave that can be heard over distances up to 25 km, depending on the wind. the heating of a narrow channel to ~24000K. It was only in the late 1800s that the true physical causes were discovered by the scientific community i.e. Early explanations of this phenomenon included fights between Zeus and his subordinates in Greek mythology, or the collision of clouds in the sky by Aristotle. Thunder has intrigued and frightened humans for millennia. Thunder is defined as the sound signature associated to the shock wave produced after a lightning discharge.
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