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 (cp Middle Dutch donre, and Old Norse þorr , Old Frisian þuner, Old High German donar 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 Gaulish Taranis and Hittite Tarhunt .

Cause

The cause of thunder has been the subject of centuries of speculation and scientific inquiry. [5] 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). [6] The Roman philosopher Lucretius held it was from the sound of hail colliding within clouds. [6]

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. [5]

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. [7] [6] 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). [8] 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, [9] similar in principle to the shock wave formed by an explosion, or at the front of a supersonic aircraft.

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. [10] [7] Other causes have also been proposed, relying on electrodynamic effects of the massive current acting on the plasma in the bolt of lightning. [11]

Consequences

The shock wave in thunder is sufficient to cause property damage [5] and injury, such as internal contusion, to individuals nearby. [12] Thunder can rupture the eardrums of people nearby, leading to permanently impaired hearing. [5] Even if not, it can lead to temporary deafness. [5]

Types

Vavrek et al. (n.d.) reported that the sounds of thunder fall into categories based on loudness, duration, and pitch. [5] 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. [13]

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. 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). [14] 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. [5] 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. [5]

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 rate of travel that exceeds the speed of sound

Supersonic travel is a rate of travel 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.

Thunderstorm Type of weather with lightning and thunder

A thunderstorm, also known as an electrical storm or a lightning storm, is a storm characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere, known as thunder. Relatively weak thunderstorms are sometimes called thundershowers. Thunderstorms occur in a type of cloud known as a cumulonimbus. They are usually accompanied by strong winds, and often produce heavy rain and sometimes snow, sleet, or hail, but some thunderstorms produce little precipitation or no precipitation at all. Thunderstorms may line up in a series or become a rainband, known as a squall line. Strong or severe thunderstorms include some of the most dangerous weather phenomena, including large hail, strong winds, and tornadoes. Some of the most persistent severe thunderstorms, known as supercells, rotate as do cyclones. While most thunderstorms move with the mean wind flow through the layer of the troposphere that they occupy, vertical wind shear sometimes causes a deviation in their course at a right angle to the wind shear direction.

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 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 an object moving faster than the speed of sound

A sonic boom is the sound associated with the shock waves created whenever 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 nineteenth century reports describe balls that eventually explode and leave behind an odor of sulfur. Descriptions of ball lightning appear in a variety of anecdotes over the centuries, but most scientists have treated reports of ball lightning skeptically. 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.

Static electricity imbalance of electric charges within or on the surface of a material

Static electricity is an imbalance of electric charges within or on the surface of a material. The charge remains until it is able to move away by means of an electric current or electrical discharge. Static electricity is named in contrast with current electricity, which flows through wires or other conductors and transmits energy.

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

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Index of meteorology articles Wikipedia index

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Atmospheric electricity Electricity in planetary atmospheres

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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), is upward propagating lightning initiated from a tall grounded object and reaches into the clouds. About 25% of all lightning events worldwide are strikes between the atmosphere and earth-bound objects. The bulk of lightning events are intra-cloud (IC) or 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.

Skyquakes are unexplained reports of a phenomenon that sounds like a cannon, trumpet or a sonic boom coming from the sky. The sound produces shock wave that can vibrate a building or a particular area. They have been heard in several locations around the world. Such locations include the banks of the river Ganges, Marwari village in Himachal Pradesh, the East Coast and inland Finger Lakes of the United States, the Magic Valley in South Central Idaho of the United States, Southern Canada, as well as areas of the North Sea, Japan, Australia, Italy, Drogheda, Bettystown, Slane, Dundalk, Ireland, Pune, Ambala, The Netherlands, Norway, Bengaluru, Tierra del Fuego Argentina, United Kingdom and recently in Jakarta, West Java, Brazil, Uruguay, in Tampico, Mexico, on May 11 2020 in Central Java and on May 21 2020 in Bandung, West Java.

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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.

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References

  1. ↑ "Severe Weather 101: Lightning Basics". nssl.noaa.gov. Retrieved October 23, 2019.
  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. 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
  6. 1 2 3 Heidorn, K. C. (1999). Thunder: Voice of the heavens. Retrieved from http://www.islandnet.com/~see/weather/elements/thunder1.htm
  7. 1 2 Rakov, Vladimir A.; Uman, Martin A. (2007). Lightning: Physics and Effects. Cambridge, England: Cambridge University Press. p. 378. ISBN   978-0-521-03541-5.,
  8. ↑ Cooray, Vernon (2003). The lightning flash . London: Institution of Electrical Engineers. pp.  163–164. ISBN   978-0-85296-780-5.
  9. ↑ "Thunder". Encyclopædia Britannica. Archived from the original on 2008-06-07. Retrieved 2008-09-12.
  10. ↑ MacGorman, Donald R.; Rust, W. David (1998). The Electrical Nature of Storms. Oxford University Press. pp. 102–104. ISBN   978-0195073379. Archived from the original on 2014-06-28. Retrieved 2012-09-06.
  11. ↑ P Graneau (1989). "The cause of thunder". J. Phys. D: Appl. Phys. 22 (8): 1083–1094. Bibcode:1989JPhD...22.1083G. doi:10.1088/0022-3727/22/8/012.
  12. ↑ 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.
  13. ↑ 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.
  14. ↑ 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.
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