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Thunder is the
sound In physics, sound is a vibration that propagates as an acoustic wave, through a transmission medium such as a gas, liquid or solid. In human physiology and psychology, sound is the ''reception'' of such waves and their ''perception'' by the ...
caused by
lightning Lightning is a naturally occurring electrostatic discharge during which two electric charge, electrically charged regions, both in the atmosphere or with one on the land, ground, temporarily neutralize themselves, causing the instantaneous ...
. Depending upon the distance from and nature of the lightning, it can range from a long, low rumble to a sudden, loud crack. The sudden increase in
temperature Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied o ...
and hence
pressure Pressure (symbol: ''p'' or ''P'') is the force applied perpendicular to the surface of an object per unit area over which that force is distributed. Gauge pressure (also spelled ''gage'' pressure)The preferred spelling varies by country and e ...
caused by the lightning produces rapid expansion of the air in the path of a lightning bolt. In turn, this expansion of air creates a sonic shock wave, often referred to as a "thunderclap" or "peal of thunder". The scientific study of thunder is known as ''brontology'' and the irrational fear (
phobia A phobia is an anxiety disorder defined by a persistent and excessive fear of an object or situation. Phobias typically result in a rapid onset of fear and are usually present for more than six months. Those affected go to great lengths to avo ...
) of thunder is called ''brontophobia''.


Etymology

The ''d'' in Modern English ''thunder'' (from earlier
Old English Old English (, ), or Anglo-Saxon, is the earliest recorded form of the English language, spoken in England and southern and eastern Scotland in the early Middle Ages. It was brought to Great Britain by Anglo-Saxon settlement of Britain, Anglo ...
''þunor'') is
epenthetic In phonology, epenthesis (; Greek language, Greek ) means the addition of one or more sounds to a word, especially in the beginning syllable (''prothesis (linguistics), prothesis'') or in the ending syllable (''paragoge'') or in-between two syll ...
, and is now found as well in Modern Dutch ''donder'' (cf.
Middle Dutch Middle Dutch is a collective name for a number of closely related West Germanic dialects whose ancestor was Old Dutch. It was spoken and written between 1150 and 1500. Until the advent of Modern Dutch after 1500 or c. 1550, there was no overarch ...
''donre''; also
Old Norse Old Norse, Old Nordic, or Old Scandinavian, is a stage of development of North Germanic languages, North Germanic dialects before their final divergence into separate Nordic languages. Old Norse was spoken by inhabitants of Scandinavia and t ...
''
þorr Thor (; from non, Þórr ) is a prominent god in Germanic paganism. In Norse mythology, he is a hammer-wielding god associated with lightning, thunder, storms, sacred groves and trees, strength, the protection of humankind, hallowing, and ...
'',
Old Frisian Old Frisian was a West Germanic language spoken between the 8th and 16th centuries along the North Sea coast, roughly between the mouths of the Rhine and Weser rivers. The Frisian settlers on the coast of South Jutland (today's Northern Friesl ...
''þuner'',
Old High German Old High German (OHG; german: Althochdeutsch (Ahd.)) is the earliest stage of the German language, conventionally covering the period from around 750 to 1050. There is no standardised or supra-regional form of German at this period, and Old High ...
''donar'', all ultimately descended from
Proto-Germanic Proto-Germanic (abbreviated PGmc; also called Common Germanic) is the reconstructed proto-language of the Germanic branch of the Indo-European languages. Proto-Germanic eventually developed from pre-Proto-Germanic into three Germanic branc ...
*''þunraz''). In
Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...
the term was ''tonare'' "to thunder". The name of the Nordic god
Thor Thor (; from non, Þórr ) is a prominent god in Germanic paganism. In Norse mythology, he is a hammer-wielding æsir, god associated with lightning, thunder, storms, sacred trees and groves in Germanic paganism and mythology, sacred groves ...
comes from the
Old Norse Old Norse, Old Nordic, or Old Scandinavian, is a stage of development of North Germanic languages, North Germanic dialects before their final divergence into separate Nordic languages. Old Norse was spoken by inhabitants of Scandinavia and t ...
word for thunder. The shared
Proto-Indo-European root The root (linguistics), roots of the reconstructed Proto-Indo-European language (PIE) are basic parts of words that carry a lexical (semiotics), lexical meaning, so-called morphemes. PIE roots usually have verbal meaning like "to eat" or "to run ...
is *''tón-r̥'' or ''*'', also found in Gaulish ''
Taranis In Celtic mythology, Taranis (Proto-Celtic: *''Toranos'', earlier ''*Tonaros''; Latin: Taranus, earlier Tanarus) is the god of thunder, who was worshipped primarily in Gaul, Hispania, Britain, and Ireland, but also in the Rhineland and Danube r ...
''.


Cause

The cause of thunder has been the subject of centuries of speculation and scientific
inquiry An inquiry (also spelled as enquiry in British English) is any process that has the aim of augmenting knowledge, resolving doubt, or solving a problem. A theory of inquiry is an account of the various types of inquiry and a treatment of the ...
.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 Early thinking was that it was made by deities, but the ancient
Greek philosophers Ancient Greek philosophy arose in the 6th century BC, marking the end of the Greek Dark Ages. Greek philosophy continued throughout the Hellenistic period and the period in which Greece and most Greek-inhabited lands were part of the Roman Empire ...
attributed it to natural causes, such as wind striking
clouds In meteorology, a cloud is an aerosol consisting of a visible mass of miniature liquid droplets, frozen crystals, or other particles suspended in the atmosphere of a planetary body or similar space. Water or various other chemicals may com ...
(
Anaximander Anaximander (; grc-gre, Ἀναξίμανδρος ''Anaximandros''; ) was a pre-Socratic Greek philosopher who lived in Miletus,"Anaximander" in ''Chambers's Encyclopædia''. London: George Newnes, 1961, Vol. 1, p. 403. a city of Ionia (in moder ...
,
Aristotle Aristotle (; grc-gre, Ἀριστοτέλης ''Aristotélēs'', ; 384–322 BC) was a Greek philosopher and polymath during the Classical period in Ancient Greece. Taught by Plato, he was the founder of the Peripatetic school of phil ...
) and movement of air within clouds (
Democritus Democritus (; el, Δημόκριτος, ''Dēmókritos'', meaning "chosen of the people"; – ) was an Ancient Greek pre-Socratic philosopher from Abdera, primarily remembered today for his formulation of an atomic theory of the universe. No ...
).Heidorn, K. C. (1999). Thunder: Voice of the heavens. Retrieved fro
http://www.islandnet.com/~see/weather/elements/thunder1.htm
The Roman philosopher
Lucretius Titus Lucretius Carus ( , ;  – ) was a Roman poet and philosopher. His only known work is the philosophical poem ''De rerum natura'', a didactic work about the tenets and philosophy of Epicureanism, and which usually is translated into E ...
held it was from the sound of
hail Hail is a form of solid precipitation. It is distinct from ice pellets (American English "sleet"), though the two are often confused. It consists of balls or irregular lumps of ice, each of which is called a hailstone. Ice pellets generally fal ...
colliding within clouds. In the mid 19th century, the accepted theory was that lightning produced a
vacuum A vacuum is a space devoid of matter. The word is derived from the Latin adjective ''vacuus'' for "vacant" or "void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists often dis ...
and that the collapse of that vacuum produced what is known as thunder. In the 20th century a consensus evolved that thunder must begin with a
shock wave In physics, a shock wave (also spelled shockwave), 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 med ...
in the air due to the sudden thermal expansion of the
plasma Plasma or plasm may refer to: Science * Plasma (physics), one of the four fundamental states of matter * Plasma (mineral), a green translucent silica mineral * Quark–gluon plasma, a state of matter in quantum chromodynamics Biology * Blood pla ...
in the lightning channel., 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 . 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, similar in principle to the shock wave formed by an
explosion An explosion is a rapid expansion in volume associated with an extreme outward release of energy, usually with the generation of high temperatures and release of high-pressure gases. Supersonic explosions created by high explosives are known ...
, or at the front of a
supersonic 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 . Speeds greater than five times ...
aircraft An aircraft is a vehicle that is able to fly by gaining support from the air. It counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines ...
. In close proximity to the source, the
sound pressure level Sound pressure or acoustic pressure is the local pressure deviation from the ambient (average or equilibrium) atmospheric pressure, caused by a sound wave. In air, sound pressure can be measured using a microphone, and in water with a hydrophone ...
of thunder is usually 165 to 180 dB, but can exceed 200 dB in some cases. 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. Other causes have also been proposed, relying on
electrodynamic In physics, electromagnetism is an interaction that occurs between particles with electric charge. It is the second-strongest of the four fundamental interactions, after the strong force, and it is the dominant force in the interactions of a ...
effects of the enormous current acting on the plasma in the bolt of lightning.


Consequences

The shock wave in thunder is sufficient to cause property damage and injury, such as internal
contusion A bruise, also known as a contusion, is a type of hematoma of tissue, the most common cause being capillaries damaged by trauma, causing localized bleeding that extravasates into the surrounding interstitial tissues. Most bruises occur close ...
, to individuals nearby. Thunder can rupture the
eardrum In the anatomy of humans and various other tetrapods, the eardrum, also called the tympanic membrane or myringa, is a thin, cone-shaped membrane that separates the external ear The outer ear, external ear, or auris externa is the extern ...
s of people nearby, leading to permanently impaired hearing. Even if not, it can lead to temporary deafness.


Types

Vavrek et al. (n.d.) reported that the sounds of thunder fall into categories based on
loudness In acoustics, loudness is the subjectivity, subjective perception of sound pressure. More formally, it is defined as, "That attribute of auditory sensation in terms of which sounds can be ordered on a scale extending from quiet to loud". The rel ...
, duration, and pitch. ''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 sounds 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. Cloud-to-ground lightning (CG) typically consists of two or more return strokes, from ground to cloud. Later return strokes have greater acoustic energy than the first.


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 The speed of light in vacuum, commonly denoted , is a universal physical constant that is important in many areas of physics. The speed of light is exactly equal to ). According to the special theory of relativity, is the upper limit ...
being much greater than the
speed of sound The speed of sound is the distance travelled per unit of time by a sound wave as it propagates through an elastic medium. At , the speed of sound in air is about , or one kilometre in or one mile in . It depends strongly on temperature as w ...
. The speed of sound in dry air is approximately or at . This translates to ; 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. 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. 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.


See also

*
Brontophobia Astraphobia, also known as astrapophobia, brontophobia, keraunophobia, or tonitrophobia, is an abnormal fear of thunder and lightning or an unwarranted fear of scattered and/or isolated thunderstorms, a type of specific phobia. It is a treatable p ...
(fear of thunder) * Castle Thunder sound effect *
Lightning Lightning is a naturally occurring electrostatic discharge during which two electric charge, electrically charged regions, both in the atmosphere or with one on the land, ground, temporarily neutralize themselves, causing the instantaneous ...
*
List of thunder gods Polytheistic peoples from many cultures have postulated a thunder god, the personification or source of the forces of thunder and lightning; a lightning god does not have a typical depiction, and will vary based on the culture. In Indo-European c ...
* Mistpouffers *
Thunderbolt A thunderbolt or lightning bolt is a symbolic representation of lightning when accompanied by a loud thunderclap. In Indo-European mythology, the thunderbolt was identified with the 'Sky Father'; this association is also found in later Hell ...
*
Thunderstorm 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 someti ...


References


External links

*
The Science of Thunder
- National Lightning Safety Institute

by Keith C. Heidorn, PhD, ACM * Wikibooks: Engineering Acoustics/Thunder acoustics
Storm: Thunder sounds in binaural audio
{{Authority control Lightning Noise Severe weather and convection Meteorological phenomena ja:雷#雷鳴 fi:Ukkonen sv:Åska