Thunder

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Cumulonimbus clouds often form thunderstorms. Anvil shaped cumulus panorama edit crop.jpg
Cumulonimbus clouds often form thunderstorms.

Thunder is the sound caused by lightning. [1] [2] [3] Depending on the distance from and nature of the lightning, it can range from a sharp, loud crack to a long, low rumble (brontide). The sudden increase in pressure and temperature from lightning produces rapid expansion of the air within and surrounding the path of a lightning strike. In turn, this expansion of air creates a sonic shock wave, often referred to as a "thunderclap" or "peal of thunder". The study of thunder is known as brontology.

Contents

Etymology

The d in Modern English thunder (from earlier Old English þunor) is epenthetic, and is now found as well in Modern Dutch donder (cf. Middle Dutch donre; also Old Norse þorr , Old Frisian þuner, Old High German donar, all ultimately descended from Proto-Germanic *þunraz). In Latin the term was tonare "to thunder". The name of the Nordic god Thor comes from the Old Norse word for thunder. [4]

The shared Proto-Indo-European root is *tón-r̥ or *tar-, also found in Gaulish Taranis . [5]

Cause

The cause of thunder has been the subject of centuries of speculation and scientific inquiry. [6] Early thinking was that it was made by deities, but the ancient Greek philosophers attributed it to natural causes, such as wind striking clouds (Anaximander, Aristotle) and movement of air within clouds (Democritus). [7] The Roman philosopher Lucretius held it was from the sound of hail colliding within clouds. [7]

By the mid-19th century, the accepted theory was that lightning produced a vacuum; the collapse of that vacuum produced what is known as thunder. [6]

In the 20th century a consensus evolved that thunder must begin with a shock wave in the air due to the sudden thermal expansion of the plasma in the lightning channel. [8] [7] The temperature inside the lightning channel, measured by spectral analysis, varies during its 50 μs existence, rising sharply from an initial temperature of about 20,000  K to about 30,000 K, then dropping away gradually to about 10,000 K. The average is about 20,400 K (20,100 °C; 36,300 °F). [9] This heating causes a rapid outward expansion, impacting the surrounding cooler air at a speed faster than sound would otherwise travel. The resultant outward-moving pulse is a shock wave, [10] similar in principle to the shock wave formed by an explosion, or at the front of a supersonic aircraft. In close proximity to the source, the sound pressure level of thunder is usually 165-180dB, but can exceed 200dB in some cases. [11]

Experimental studies of simulated lightning have produced results largely consistent with this model, though there is continued debate about the precise physical mechanisms of the process. [12] [8] Other causes have also been proposed, relying on electrodynamic effects of the enormous current acting on the plasma in the bolt of lightning. [13]

Consequences

The shock wave in thunder is sufficient to cause property damage [6] and injury, such as internal contusion, to individuals nearby. [14] Thunder can rupture the eardrums of people nearby, leading to permanently impaired hearing. [6] Even if not, it can lead to temporary deafness. [6]

Types

Vavrek et al. (n.d.) reported that the sounds of thunder fall into categories based on loudness, duration, and pitch. [6] Claps are loud sounds lasting 0.2 to 2 seconds and containing higher pitches. Peals are sounds changing in loudness and pitch. Rolls are irregular mixtures of loudness and pitches. Rumbles are less loud, last for longer (up to more than 30 seconds), and of low pitch.

Inversion thunder results when lightning strikes between cloud and ground occur during a temperature inversion; the resulting thunder sound have significantly greater acoustic energy than from the same distance in a non-inversion condition. In an inversion, the air near the ground is cooler than the higher air; inversions often occur when warm moist air passes above a cold front. Within a temperature inversion, the sound energy is prevented from dispersing vertically as it would in a non-inversion and is thus concentrated in the near-ground layer. [15]

Thunder is the sound produced by lightning. Lightning 14.07.2009 20-42-33.JPG
Thunder is the sound produced by lightning.

Cloud-ground lightning typically consist of two or more return strokes, from ground to cloud. Later return strokes have greater acoustic energy than the first.[ citation needed ]

Perception

The most noticeable aspect of lightning and thunder is that the lightning is seen before the thunder is heard. This is a consequence of the speed of light being much greater than the speed of sound. The speed of sound in dry air is approximately 343 m/s or 1,127 ft/s or 768 mph (1,236 km/h) at 20 °C (68 °F). [16] This translates to approximately 3 seconds per kilometre (5 seconds per mile); saying "one thousand and one... one thousand and two..." is a useful method of counting the seconds from the perception of a given lightning flash to the perception of its thunder (which can be used to gauge the proximity of lightning for the sake of safety).

A very bright flash of lightning and an almost simultaneous sharp "crack" of thunder, a thundercrack, therefore indicates that the lightning strike was very near.

Very close[ quantify ] thunder cracks

Close-in lightning has been described first as a clicking or cloth-tearing sound, then a cannon shot sound or loud crack/snap, followed by continuous rumbling. [6] The early sounds are from the leader parts of lightning, then the near parts of the return stroke, then the distant parts of the return stroke. [6]

See also

Related Research Articles

Cumulonimbus cloud Genus of clouds, dense towering vertical cloud associated with thunderstorms and atmospheric instability

Cumulonimbus is a dense, towering vertical cloud, forming from water vapor carried by powerful upward air currents. If observed during a storm, these clouds may be referred to as thunderheads. Cumulonimbus can form alone, in clusters, or along cold front squall lines. These clouds are capable of producing lightning and other dangerous severe weather, such as tornadoes and hailstones. Cumulonimbus progress from overdeveloped cumulus congestus clouds and may further develop as part of a supercell. Cumulonimbus is abbreviated Cb.

Inversion (meteorology) Deviation from the normal change of an atmospheric property with altitude

In meteorology, an inversion, also known as a temperature inversion, is a deviation from the normal change of an atmospheric property with altitude. It almost always refers to an inversion of the thermal lapse rate. Normally, air temperature decreases with an increase in altitude. During an inversion, warmer air is held above cooler air; the normal temperature profile with altitude is inverted.

Fog Atmospheric phenomenon

Fog is a visible aerosol consisting of tiny water droplets or ice crystals suspended in the air at or near the Earth's surface. Fog can be considered a type of low-lying cloud usually resembling stratus, and is heavily influenced by nearby bodies of water, topography, and wind conditions. In turn, fog has affected many human activities, such as shipping, travel, and warfare.

Supersonic speed Speed that exceeds the speed of sound

Supersonic speed is the speed of an object that exceeds the speed of sound (Mach 1). For objects traveling in dry air of a temperature of 20 °C (68 °F) at sea level, this speed is approximately 343.2 m/s. Speeds greater than five times the speed of sound (Mach 5) are often referred to as hypersonic. Flights during which only some parts of the air surrounding an object, such as the ends of rotor blades, reach supersonic speeds are called transonic. This occurs typically somewhere between Mach 0.8 and Mach 1.2.

Lightning Weather phenomenon involving electrostatic discharge

Lightning is a naturally occurring electrostatic discharge during which two electrically charged regions in the atmosphere or ground temporarily equalize themselves, causing the instantaneous release of as much as one gigajoule of energy. This discharge may produce a wide range of electromagnetic radiation, from very hot plasma created by the rapid movement of electrons to brilliant flashes of visible light in the form of black-body radiation. Lightning causes thunder, a sound from the shock wave which develops as gases in the vicinity of the discharge experience a sudden increase in pressure. Lightning occurs commonly during thunderstorms and other types of energetic weather systems, but volcanic lightning can also occur during volcanic eruptions.

Shock wave Propagating disturbance

In physics, a shock wave, or shock, is a type of propagating disturbance that moves faster than the local speed of sound in the medium. Like an ordinary wave, a shock wave carries energy and can propagate through a medium but is characterized by an abrupt, nearly discontinuous, change in pressure, temperature, and density of the medium.

The speed of sound is the distance travelled per unit of time by a sound wave as it propagates through an elastic medium. At 20 °C (68 °F), the speed of sound in air is about 343 metres per second, or a kilometre in 2.9 s or a mile in 4.7 s. It depends strongly on temperature as well as the medium through which a sound wave is propagating.

Sonic boom Sound created by a object going as fast as the speed of sound

A sonic boom is a sound associated with shock waves created when an object travels through the air faster than the speed of sound. Sonic booms generate enormous amounts of sound energy, sounding similar to an explosion or a thunderclap to the human ear. The crack of a supersonic bullet passing overhead or the crack of a bullwhip are examples of a sonic boom in miniature.

Ball lightning Atmospheric electrical phenomenon

Ball lightning is an unexplained phenomenon described as luminescent, spherical objects that vary from pea-sized to several meters in diameter. Though usually associated with thunderstorms, the phenomenon is said to last considerably longer than the split-second flash of a lightning bolt. Some 19th-century reports describe balls that eventually explode and leave behind an odor of sulfur. Descriptions of ball lightning appear in a variety of accounts over the centuries and have received attention from scientists. An optical spectrum of what appears to have been a ball-lightning event was published in January 2014 and included a video at high frame rate. Laboratory experiments have produced effects that are visually similar to reports of ball lightning, but how these relate to the supposed phenomenon remains unclear.

Wind shear Difference in wind speed or direction over a short distance

Wind shear, sometimes referred to as wind gradient, is a difference in wind speed or direction over a relatively short distance in the atmosphere. Atmospheric wind shear is normally described as either vertical or horizontal wind shear. Vertical wind shear is a change in wind speed or direction with change in altitude. Horizontal wind shear is a change in wind speed with change in lateral position for a given altitude.

Heat lightning Description of distant cloud to ground lightning

Heat lightning, also known as silent lightning, summer lightning, or dry lightning, is a misnomer used for the faint flashes of lightning on the horizon or other clouds from distant thunderstorms that do not appear to have accompanying sounds of thunder.

Effects of nuclear explosions Type and severity of damage caused by nuclear weapons

The effects of a nuclear explosion on its immediate vicinity are typically much more destructive and multifaceted than those caused by conventional explosives. In most cases, the energy released from a nuclear weapon detonated within the lower atmosphere can be approximately divided into four basic categories:

Transonic

Transonic flight is flying at or near the speed of sound in "no wind". A typical convention used in aeronautics is to define transonic flight as speeds in the range of Mach 0.72 to 1.0.

Lightning strike

A lightning strike or lightning bolt is an electric discharge between the atmosphere and the ground. They mostly originate in a cumulonimbus cloud and terminate on the ground, called cloud-to-ground (CG) lightning. A less common type of strike, called ground-to-cloud (GC) lightning, is upward propagating lightning initiated from a tall grounded object and reaching into the clouds. About 69% of all lightning events worldwide are strikes between the atmosphere and earth-bound objects. Most are intra-cloud (IC) lightning and cloud-to-cloud (CC), where discharges only occur high in the atmosphere. Lightning strikes the average commercial aircraft at least once a year, but modern engineering and design means this is rarely a problem. The movement of aircraft through clouds can even cause lightning strikes.

A skyquake is a phenomenon where a loud cannon, trumpet or a sonic boom sound is reported to originate from the sky. The sound can produce shock waves that vibrate a building or a particular area.

Shock diamond

Shock diamonds are a formation of standing wave patterns that appear in the supersonic exhaust plume of an aerospace propulsion system, such as a supersonic jet engine, rocket, ramjet, or scramjet, when it is operated in an atmosphere. The "diamonds" are actually a complex flow field made visible by abrupt changes in local density and pressure as the exhaust passes through a series of standing shock waves and expansion fans. Mach diamonds are named after Ernst Mach, the physicist who first described them.

Lightning detection

A lightning detector is a device that detects lightning produced by thunderstorms. There are three primary types of detectors: ground-based systems using multiple antennas, mobile systems using a direction and a sense antenna in the same location, and space-based systems.

Muzzle flash

Muzzle flash is the light — both visible and infrared — created by a muzzle blast, which is caused by the sudden release and expansion of high-temperature, high-pressure gases from the muzzle of a firearm during shooting. Both the blast and flash are products of the exothermic combustion of the propellant (gunpowder), and any remaining unburned powders reacting with ambient air. The size and shape of the muzzle flash is dependent on the combustion energy of propellant being used, the amount of combustible ejecta remaining, and any devices attached to the muzzle.

Vapor cone

A vapor cone, also known as shock collar or shock egg, is a visible cloud of condensed water that can sometimes form around an object moving at high speed through moist air, for example, an aircraft flying at transonic speeds. When the localized air pressure around the object drops, so does the air temperature. If the temperature drops below the saturation temperature, a cloud forms.

Glossary of meteorology List of definitions of terms and concepts commonly used in meteorology

This glossary of meteorology is a list of terms and concepts relevant to meteorology and atmospheric science, their sub-disciplines, and related fields.

References

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  2. "Thunder Facts". factsjustforkids.com. Retrieved October 23, 2019.
  3. "The Sound of Thunder". weather.gov. Retrieved October 23, 2019.
  4. "thunder". Oxford English Dictionary (2 ed.). Oxford, England: Oxford University Press. 1989.
  5. Matasovic, Ranko. Etymological Dictionary Of Proto Celtic. Leiden, The Netherlands: Brill. 2009. p. 384. ISBN   978-90-04-17336-1
  6. 1 2 3 4 5 6 7 8 Vavrek, R. J., Kithil, R., Holle, R. L., Allsopp, J., & Cooper, M. A. (n.d.). The science of thunder. Retrieved from http://lightningsafety.com/nlsi_info/thunder2.html
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  11. "Ultimate Sound Pressure Level Decibel Table" . Retrieved 2020-12-13.
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  14. Fish, Raymond M (2004). "Thermal and mechanical shock wave injury". In Nabours, Robert E (ed.). Electrical injuries: engineering, medical, and legal aspects. Tucson, AZ: Lawyers & Judges Publishing. p.  220. ISBN   978-1-930056-71-8.
  15. Dean A. Pollet and Micheal M. Kordich (2013-04-08). "User's guide for the Sound Intensity Prediction System (SIPS) as installed at the Naval Explosive Ordnance Disposal Technology Division (Naveodtechdiv)". Systems Department February 2000. dtic.mil. Archived from the original on April 8, 2013.
  16. Handbook of Chemistry and Physics, 72nd edition, special student edition. Boca Raton: The Chemical Rubber Co. 1991. p. 14.36. ISBN   978-0-8493-0486-6.