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Radiation astronomy/Lightnings

Representation of upper-atmospheric lightning and electrical-discharge phenomena are displayed. Credit: Abestrobi.
An illustration of different kinds of transient luminous events (TLEs) is displayed. Credit: Carlos Miralles (AeroVironment) and Tom Nelson (FMA).{{fairuse}}

Lightning is more than ground-to-cloud electron transfer.

"Cloud flashes sometimes have visible channels that extend out into the air around the storm (cloud-to-air or CA), but do not strike the ground. The terms sheet lightning or intra-cloud lightning (IC) refers to lightning embedded within a cloud that lights up as a sheet of luminosity during the flash. A related term, heat lightning, is lightning or lightning-induced illumination that is too far away for thunder to be heard. Lightning can also travel from cloud-to-cloud (CC). Spider lightning refers to long, horizontally traveling flashes often seen on the underside of stratiform clouds."[1]

"Large thunderstorms are capable of producing other kinds of electrical phenomena called transient luminous events (TLEs) that occur high in the atmosphere. They are rarely observed visually and not well understood. The most common TLEs include red sprites, blue jets, and elves."[1]

The illustration on the left labels Elves, Sprites, and tendrils, a stratiform region producing positive cloud-to-ground flashes with spider lightning on the right to conventional cloud-to-air discharge, upward superbolt, blue jets and negative cloud-to-ground flash near convective core. Approximate altitudes in the Earth's atmosphere and ionosphere are indicated.

Natural electric field of the EarthEdit

 
Thunderheads near Borneo, Indonesia are featured in this image photographed by an Expedition 40 crew member on the International Space Station. Credit: M. Justin Wilkinson, Jacobs and Michael Trenchard, Barrios Technology at NASA-JSC.

The natural electric field of the Earth refers to the planet Earth having a natural direct current (DC) electric field or potential gradient from the ground upwards to the ionosphere. The static fair-weather electric field in the atmosphere is ~150 volts per meter (V/m) near the Earth's surface, but it drops exponentially with height to under 1 V/m at 30 km altitude, as the conductivity of the atmosphere increases.

"In this image [on the right], late afternoon sunlight casts long shadows from thunderhead anvils down onto southern Borneo. Near the horizon (image top center), more than 1000 kilometers away from the space station, storm formation is assisted by air currents rising over the central mountains of Borneo."[2]

"Winds usually blow in different directions at different altitudes. At the time of this photo, high-altitude winds were clearly sweeping the tops off the many tallest thunderclouds, generating long anvils of diffuse cirrus plumes that trail south. At lower levels of the atmosphere, “streets” of white dots—fair-weather cumulus clouds—are aligned with west-moving winds. Small smoke plumes from forest fires in Borneo are also aligned west."[2]

The surface of the Earth is negatively charged, carrying 500,000 Coulombs (C) of electric charge (500 kC),[3] and is at 300,000 volts (V), 300 kV,[4] relative to the positively charged ionosphere. There is a constant flow of electricity, at around 1350 amperes (A) [approximately 1100 A][4], and resistance of the Earth's atmosphere is around 220 Ohms.[3] This gives a power of around 400 megawatts (MW). There are several theoretical proposals to harvest this power that Nikola Tesla elaborated (around 1901) and his followers. The main principle is to mimic the conditions when charged particles from space interact with the higher and lower layers of Earth's atmosphere. In any case averages a mere 0.8 microwatts per square metre of the earth's surface (compare solar radiation which is one billion times as large).

The charge is maintained by the stream of charged particles from the Sun. This process affects the ionosphere, as well as the troposphere, possibly causing thunderstorms. The electrical energy stored in the Earth's atmosphere is around 150 gigajoules (GJ).

The Earth-ionosphere system acts as a giant capacitor, of capacity 1.8 Farads.

The Earth's surface carries around -1 nC of electric charge per square meter.

Lightning theoryEdit

 
Russia’s Soyuz-2 rocket was hit by lightning shortly after its launch on 27 May 2019. Credit: Roscosmos/Ministry of Defense of the Russian Federation/Dmitry Rogozin.{{fairuse}}

Def. a "flash of light produced by short-duration, high-voltage discharge of electricity within a cloud, between clouds, or between a cloud and the earth"[5] is called lightning.

A typical cloud-to-ground lightning flash culminates in the formation of an electrically conducting plasma channel through the air in excess of 5 km (3.1 mi) tall, from within the cloud to the ground's surface. The actual discharge is the final stage of a very complex process.[6] At its peak, a typical thunderstorm produces three or more strikes to the Earth per minute.[7] Lightning primarily occurs when warm air is mixed with colder air masses.[8] However, it can also occur during dust storms, forest fires, tornadoes, volcanic eruptions, and even in the cold of winter, where the lightning is known as thundersnow.[9][10] Hurricanes typically generate some lightning, mainly in the rainbands as much as 160 km (99 mi) from the center.[11][12][13]

The image on the right demonstrates that proper electrical conduction during a rocket launch can protect the rocket, payload and prevent fuel explosions.

MagnetismEdit

 
Lightning-induced remanent magnetization (LIRM) is mapped during a magnetic field gradient survey of an archaeological site located in Wyoming, United States. Credit: .

The movement of electrical charges produces a magnetic field, where the intense currents of a lightning discharge create a fleeting but very strong magnetic field and the lightning current path passes through rock, soil, or metal these materials can become permanently magnetized, known as lightning-induced remanent magnetism, or LIRM which follow the least resistive path, often horizontally near the surface[14][15] but sometimes vertically, where faults, ore bodies, or ground water offers a less resistive path.[16] One theory suggests that lodestones, natural magnets encountered in ancient times, were created in this manner.[17]

Lightning-induced magnetic anomalies can be mapped in the ground,[18][19] and analysis of magnetized materials can confirm lightning was the source of the magnetization[20] and provide an estimate of the peak current of the lightning discharge.[21]

Magnetic fields generated by plasma may induce hallucinations in subjects located within 200 meters of a severe lightning storm.[22]

Negative lightningEdit

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 billion joules of energy.[23]

The negative end of the bidirectional leader fills a positive charge region, also called a well, inside the cloud while the positive end fills a negative charge well. Leaders often split, forming branches in a tree-like pattern.[24]

Electricity takes every path available to it.[25]

The rate at which the return stroke current travels has been found to be around 100,000 km/s.[26]

High-speed videos (examined frame-by-frame) show that most negative CG lightning flashes are made up of 3 or 4 individual strokes, though there may be as many as 30.[27]

The dart leaders making connections with the ground is what causes a majority of subsequent return strokes.[28]

Large bolts of negative lightning can carry up to 120 kA and 350 coulombs.[29]

Cloud-to-ground lightning, where lightning appears to exit from the cumulonimbus cloud and propagate a considerable distance through clear air before veering towards, and striking, the ground, are known as "bolts from the blue", which are in fact negative flashes that begin as intracloud flashes within the cloud, the negative leader then exits the cloud from the positive charge region before propagating through clear air and striking the ground some distance away.[30][31]

Clear-air lightning describes lightning that occurs with no apparent cloud close enough to have produced it: in the U.S. and Canadian Rockies, a thunderstorm can be in an adjacent valley and not observable from the valley where the lightning bolt strikes, either visually or audibly; European and Asian mountainous areas experience similar events; in areas such as sounds, large lakes or open plains, when the storm cell is on the near horizon (within 26 km (16 mi)) there may be some distant activity, a strike can occur and as the storm is so far away, the strike is referred to as a bolt from the blue.[32] These flashes usually begin as normal intracloud lightning flashes before the negative leader exits the cloud and strikes the ground a considerable distance away.[30][31] Positive clear-air strikes can occur in highly sheared environments where the upper positive charge region becomes horizontally displaced from the precipitation area.[33]

Positive lightningEdit

The reverse happens in a positive CG flash, where electrons travel upward along the lightning channel and a positive charge is transferred to the ground. Positive lightning is less common than negative lightning, and on average makes up less than 5% of all lightning strikes.[34]

There are six different mechanisms theorized to result in the formation of downward positive lightning.[35]

  • Vertical wind shear displacing the upper positive charge region of a thundercloud, exposing it to the ground below.
  • The loss of lower charge regions in the dissipating stage of a thunderstorm, leaving the primary positive charge region.
  • A complex arrangement of charge regions in a thundercloud, effectively resulting in an inverted dipole or inverted tripole in which the main negative charge region is above the main positive charge region instead of beneath it.
  • An unusually large lower positive charge region in the thundercloud.
  • Cutoff of an extended negative leader from its origin which creates a new bidirectional leader in which the positive end strikes the ground, commonly seen in anvil-crawler spider flashes.
  • The initiation of a downward positive branch from an intracloud lightning flash.

The average positive ground flash has roughly double the peak current of a typical negative flash, and can produce peak currents up to 400,000 amperes (400 kA) and charges of several hundred coulombs.[36][37] Furthermore, positive ground flashes with high peak currents are commonly followed by long continuing currents, a correlation not seen in negative ground flashes.[38]

Positive lightning tends to occur more frequently in winter storms, as with thundersnow, during intense tornadoes[39] and in the dissipation stage of a thunderstorm.[40] Huge quantities of extremely low frequency (ELF) and very low frequency (VLF) radio waves are also generated.[41]

The lightning shows that during the Southern Ontario tornado outbreak of 2005 there was a strong peak during the F2 tornadoes, dominated by the positive cloud-to-ground strikes, that this is often the case in tornadic storms, followed by a sharp drop and then another peak, but this one dominated by negative lightning during the flooding phase of the storm.[42]

The dangers of more powerful positive lightning were not understood until the destruction of a glider in 1999.[43] The 1985 standard in force in the US at the time of the glider crash, Advisory Circular AC 20-53A,[43] was replaced by Advisory Circular AC 20-53B in 2006.[44] However, it is unclear whether adequate protection against positive lightning was incorporated.[45][46]

In 2010 a lightning measurement station was installed atop a 120 m (390 ft) tall telecommunications tower on the mountain Säntis by the Electromagnetic Compatibility Lab of the EPFL in Lausanne, where in the first nine months of operation it recorded about 50 strikes, including 7 positive lightning strikes.[47]

Typical speed of a positive lightning return stroke (cf. stepped leader above) is 100,000,000 m/s, 360,000,000 km/h, 220,000,000 mph, 0.3 c.[48]

ThunderstormsEdit

 
Stages of a thunderstorm's life.
 
Anvil-shaped thundercloud in the mature stage. Credit: .
 
Lightning, which is responsible for the majority of fires in the American West. Credit: Jrmichae.

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.[49] Relatively weak thunderstorms are sometimes called thundershowers.[50]

Thunderstorms can form and develop in any geographic location but most frequently within the mid-latitude, where warm, moist air from tropical latitudes collides with cooler air from polar latitudes.[51]

Warm air has a lower density than cool air, so warmer air rises upwards and cooler air will settle at the bottom[52] (this effect can be seen with a hot air balloon).[53] Clouds form as relatively warmer air, carrying moisture, rises within cooler air. The moist air rises, and, as it does so, it cools and some of the water vapor in that rising air condenses.[54] When the moisture condenses, it releases energy known as latent heat of condensation, which allows the rising packet of air to cool less than the cooler surrounding air[55] continuing the cloud's ascension. If enough instability is present in the atmosphere, this process will continue long enough for cumulonimbus clouds to form and produce lightning and thunder. Meteorological indices such as convective available potential energy (CAPE) and the lifted index can be used to assist in determining potential upward vertical development of clouds.[56] Generally, thunderstorms require three conditions to form:

  1. Moisture
  2. An unstable airmass
  3. A lifting force (heat)

All thunderstorms, regardless of type, go through three stages: the developing stage, the mature stage, and the dissipation stage.[57] The average thunderstorm has a 24 km (15 mi) diameter. Depending on the conditions present in the atmosphere, each of these three stages take an average of 30 minutes.[58]

A "thunderstorm supplies a negative charge to the Earth. The net positive space charge in the air between the ground and a height of ~ 10 km is nearly equal to the negative charge on the Earth's surface".[59]

'Giant' "thunderclouds can produce transverse electric fields of tens of microvolts per meter in the equatorial plane of the midlatitude magnetosphere."[60]

The "contribution to global thunderstorm activity by oceanic thunderstorms should be regarded as itself having a diurnal variation of some 18% in amplitude."[61]

Pyrocumulonimbus are cumuliform clouds that can form over a large fire and that are particularly dry.[62]

There is "a decrease in thunderstorms at the time of high cosmic rays and an increase in thunderstorms 2-4 days later."[63]

ElvesEdit

"A third phenomenon was discovered in video from the STS-41 mission (October 1990) in the lower ionosphere directly above an active thunderstorm. It consisted of a large horizontal brightening several hundred kilometers across at the altitude of the airglow layer. In 1995, Lyons and associates confirmed the existence of this type of very brief brightening which they named Emissions of Light and Very Low Frequency Perturbations From Electromagnetic Pulse Sources (ELVES)."[64]

"When the lightning phenomena were viewed from a different vantage point - from above the thunderstorms (e.g., from space, aircraft or mountaintop) - new discoveries were made and insights gained into the upper atmospheric optical flashes now commonly referred to as sprites, jets, starters, and ELVES."[64]

"There are no historical reports from eyewitnesses describing the phenomenon that is now called "Emission of Light and Very Low Frequency Perturbations From Electro-magnetic Pulse Sources" or ELVES (Lyons and Nelson, 1995). The one millisecond lifetime of this phenomenon explains why there have been no eyewitness accounts describing a brief flash that would fill the entire night sky for any observer within a 100 km radius from the causative lightning flash. Inan (1990) and Inan et al. (1991) predicted the existence of strong Joule heating of the base of the ionosphere by the electromagnetic pulses of natural lightning."[64]

"After fifteen sprites and one jet had been identified in the shuttle video, a distinctively different event was discovered in shuttle video acquired on October 7, 1990 directly above an active thunderstorm off the coast of French Guyana (Boeck et al., 1992). A large horizontal flash appeared at the altitude of the airglow layer. It occurred in the video field before the appearance of main lightning flash in a thunderstorm that was near the limb of the Earth. They concluded that the causative lightning flash occurred slightly after the video scan passed the location of the storm image. There was a clear view of the mesosphere below the airglow layer, but there was no indication of a sprite in the video sequence (although a sprite event was captured 4½ hours earlier under similar moonlight conditions). A search of the shuttle video failed to produce a second example of this type of horizontal flash. Since it was clear that this was not an example of a sprite or a jet, the observations were published on the basis of this single example. The video was presented at the 1991 Spring AGU meeting (Boeck et al., 1991a) as well as at the Aerospace Lightning Conference (Boeck et al., 1991b). To promote a better understanding of these new phenomena as seen from space, Vaughan distributed a number of video tapes to various researchers who had express an interest in the phenomena. Seminars based on the video tape observations were given at Los Alamos National Laboratory and Stanford University. Researchers at both of these institutions have made major contributions to the theory of Sprite and ELVES phenomena."[64]

"Several years passed before there was a second successful measurement of the ELVES phenomenon. On June 23, 1995 Lyons et al. (1995) and Fukunishi et al. (1996) confirmed the existence of a flash similar to the airglow flash seen earlier in the shuttle data, and Lyons et al. (1995) gave it the name Emissions of Light and Very Low Frequency Perturbations From Electromagnetic Pulse Sources (ELVES). Lyons presented video images captured by a low-light-level TV camera sited near Ft. Collins, Colorado. The ELVES phenomenon has a characteristic event duration of one millisecond (Fukunishi, 1996)."[64]

SpritesEdit

 
This is the first color image of a sprite. Credit: Eastview.
 
The image shows an example of jellyfish lightning or sprites. Credit: H. H. C. Stenbaek-Nielsen.

"The phenomenon, now known as a sprite, was first accidently documented on ground based videotape recordings on the night of July 6, 1989. Video observations from the space shuttle acquired from 1989 through 1991 provided 17 additional examples to confirm the existence of the sprites phenomenon."[64]

"Throughout the historical scientific literature, there are sprinklings of eyewitness accounts of unusual "lightning" observed in the clear air above nighttime thunderstorms. The descriptions use phases such as "continuous darts of light... ascended to a considerable altitude, resembling rockets more than lightning." (MacKenzie and Toynbee, 1886), "a luminous trail shot up to 15 degrees or so, about as fast as, or faster than, a rocket" (Everett, 1903), "a long weak streamer of a reddish hue" (Malan, 1937), "flames appearing to rise from the top of the cloud" (Ashmore, 1950), or "the discharge assumed a shape similar to roots of a tree in an inverted position" (Wood, 1951). Partly because these eyewitness reports of unusual "lightning" appearing above thunderstorms were never captured on film, the lightning science community generally ignored them. The lack of an established vocabulary and the existence of several distinctive phenomena contributed to the variation in the verbal descriptions."[64]

"[Boccippio et al., 1994] has shown that these bright discharges are associated with large amplitude return strokes bringing positive charge downward. In fact, a positive return stroke accompanied the only MLE sprite recorded within range of a ground based lightning detection network. The videos showed that additional discharges continued in the clouds after a sprite for a total mean time of a second, which can be interpreted as evidence for a continuing current. All together, this was strong evidence that the sprite above the thunderstorm was caused, directly or indirectly, by an energetic lightning discharge."[64]

The "range to the sprites was well over 1000 kilometers [...] The width of the sprites varied considerably from very thin or even several thin filaments to broad columns some kilometers across, while the bright "head" (when visible) had dimensions on the order of kilometers."[64]

"The optical and RF measurements collected during the 1994 field campaign rapidly uncovered the basic properties of sprites (Lyons, 1994; Lyons and Williams, 1994; Lyons et al., 1994; Sentman et al., 1994; Sentman et al., 1995; Wescott et al., 1994; Lyons et al., 1995a,b). Other workers (e.g., Boccippio, 1994) established the causal association of sprites with positive cloud-to-ground lightning discharges."[64]

Sprites "are typically associated with low flash rate cells [...] The shuttle videos established that lightning directly or indirectly causes sprites."[64]

The first "color image of a sprite [...] was obtained during a 1994 NASA/University of Alaska aircraft campaign to study sprites. The event was captured using an intensified color TV camera. The red color was subsequently determined to be from nitrogen fluorescent emissions excited by a lightning stroke in the underlying thunderstorm."[65]

"During a thunderstorm, high in the ionosphere, you’ll find an odd variety of lightning that is far above the thunderstorm itself. Jellyfish lightning, also known as sprites, are red flashes of light that last for a few seconds. They can have a wide bell-shaped top and tentacle-like wisps of light at the bottom, resembling a jellyfish."[66]

"In high-speed videos we can see the dynamics of sprite formation and then use that information to model and to reproduce the dynamics."[67]

"These sprites only occur during thunderstorms, though sprites are about three times higher up than storms. [...] the storms are necessary for sprites to occur, they aren’t quite sufficient enough to cause them on their own [...] The tentacle-like tendrils at the bottom were shown to form much faster than the bell-shaped top. [...] localized plasma irregularities can spark the formation of a sprite."[66]

Sprites are large-scale electrical discharges which occur high above a thunderstorm cloud, or cumulonimbus, giving rise to a quite varied range of visual shapes, triggered by the discharges of positive lightning between the thundercloud and the ground.[41] The phenomena were named after the mischievous sprite, e.g., Shakespeare's Ariel or Puck,[68] and is also an acronym for Stratospheric/mesospheric Perturbations Resulting from Intense Thunderstorm Electrification.[69] They normally are colored reddish-orange or greenish-blue, with hanging tendrils below and arcing branches above. They can also be preceded by a reddish halo. They often occur in clusters, lying 50 kilometres (31 mi) to 90 kilometres (56 mi) above the Earth's surface. Sprites have been witnessed thousands of times.[70] Sprites have been held responsible for otherwise unexplained accidents involving high altitude vehicular operations above thunderstorms.[71]

Blue jetsEdit

"In the summer of 1994, Wescott and associates (Wescott et al., 1994; Wescott et al., 1995a,b) confirmed the existence of jets and named the phenomena blue jets when they recorded a very active thunderstorm in Arkansas, USA using both a low-light-level monochrome and a color video cameras. The video was collected during a nighttime research flight using two aircraft that were flying around the thunderstorm. During this flight, color video imagery established that jets are blue in color and sprites are red. A total of 52 jets were seen during a 20-minute time span. The jets developed over several video frames, with a characteristic time of the order of 100 ms and propagation speeds similar to that of a step leader process (i.e., ~ 105 m/s). The video released after this flight proved to be a turning point in establishing wide interest in these phenomena. The spectacular multiple close-up images of these jets completely overshadowed the single, poorly resolved jet observation from the space shuttle."[64]

Blue jets differ from sprites in that they project from the top of the cumulonimbus above a thunderstorm, typically in a narrow cone, to the lowest levels of the ionosphere 40 to 50 km (25 to 30 miles) above the earth. In addition, whereas red sprites tend to be associated with significant lightning strikes, blue jets do not appear to be directly triggered by lightning (they do, however, appear to relate to strong hail activity in thunderstorms).[72] They are also brighter than sprites and, as implied by their name, are blue in color. The color is believed to be due to a set of blue and near-ultraviolet emission lines from neutral and ionized molecular nitrogen.

Blue startersEdit

Blue "starters (Wescott et al., 1995) [are] an upward moving luminous phenomenon closely related to blue jets."[64]

Gigantic jetsEdit

 
This is a gigantic jet observed over a thunderstorm. Credit: Welias.
 
This is an image of a gigantic jet above a thunderstorm near the Philippines. Credit: H. T. Su, R. R. Hsu, A. B. Chen, Y. C. Wang, W. S. Hsiao, W. C. Lai, L. C. Lee, M. Sato & H. Fukunishi.

"On February 02, 2014, the Oro Verde Observatory (República Argentina) reported 10 or more gigantic jet event[s] observed over a thunderstorm in Entre Ríos south. Storm center [is] located at 33°S, 60°W, near the Rosario city."[73]

Each gigantic "jet could transfer 30 coulombs of negative charge from the clouds to the ionosphere (H T Su et al. 2003 Nature 423 974)."[74]

"During a thunderstorm in the South China Sea in July 2002, Su and co-workers used low-light-level cameras to photograph the clouds every 17 milliseconds. The five jets they observed - dubbed carrot-jets or tree-jets according to their shapes - were visible for some tens of milliseconds. But crucially, the team also detected simultaneous bursts of radio waves in four of the five cases, which indicates that the jets had transferred significant amounts of charge. The thunderclouds were at an altitude of 16 km."[74]

"Such electromagnetic bursts have only previously been linked with powerful lightning strikes, which are known to transfer large quantities of charge. But [lightning may not have] triggered the radio waves they detected, since the local lightning detection network registered no strikes at the times of the jets."[74]

On the left is an image of a fully developed gigantic jet above a thunderstorm near the Philippine.

Gamma raysEdit

The red dots show some of the ~500 terrestrial gamma-ray flashes daily detected by the Fermi Gamma-ray Space Telescope through 2010. Credit: NASA/Goddard Space Flight Center.

"A number of observations by space-based telescopes have revealed ... gamma ray emissions ... terrestrial gamma-ray flashes (TGFs). These observations pose a challenge to current theories of lightning, especially with the discovery of the clear signatures of antimatter produced in lightning.[75]

A TGF has been linked to an individual lightning stroke occurring within 1.5 ms of the TGF event,[76] proving for the first time that the TGF was of atmospheric origin and associated with lightning strikes.

The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) spacecraft, as reported by David Smith of University of California (UC) Santa Cruz, has been observing TGFs at a much higher rate, indicating that these occur about 50 times per day globally (still a very small fraction of the total lightning on the planet). The energy levels recorded exceed 20 MeV. Apparently, the gamma radiation fountains upward from starting points at surprisingly low altitudes in thunderclouds. Steven Cummer, from Duke University's Pratt School of Engineering, said, "These are higher energy gamma rays than come from the sun. And yet here they are coming from the kind of terrestrial thunderstorm that we see here all the time." In 2009, the Fermi Gamma Ray Telescope in Earth orbit observed an intense burst of gamma rays corresponding to positron annihilations coming out of a storm formation. Scientists wouldn't have been surprised to see a few positrons accompanying any intense gamma ray burst, but the lightning flash detected by Fermi appeared to have produced about 100 trillion positrons. This has been reported by media in January 2011, it is an effect, never considered to happen before.[77]

AtmospheresEdit

Charge is apparently replaced by the action of thunderstorms including lightning. The thunderstorm system acts as a type of battery to keep the fine weather system charged."[78]

Solar windsEdit

 
A lightning storm over England is imaged. Credit: Catalin Fatu.

"The sun spits out charged particles that hit our atmosphere two to four days later at 1.5-2.7 million kph, but it does not do so evenly."[79]

"The solar wind is not continuous, it has slow and fast streams. Because the Sun rotates, these streams can be sent out behind each other - so if you have a fast solar wind catching up with a slow solar wind, it causes a concentration to occur."[80]

"The slow phase is composed similarly to the solar corona while fast particles have a composition close to that of the photosphere, the outer layer of the sun that produces the light."[79]

There is "a 31% increase in average lightning strikes over central England (422 to 321) in the 40 days after major solar wind events compared to the days beforehand. Lightning peaked 12-18 days after the wind's arrival. A matching increase in thundery days provided supporting evidence."[79]

"It's unexpected, because these streams of particles bring with them an enhanced magnetic field - and this shields Earth from the very high-energy cosmic rays from outside of the Solar System.”[80]

"The reduction in cosmic rays is only around 1%, but still noticeable. Cosmic rays emitted by supernovae are thought to trigger lighting strikes, and it was expected that the shielding effect of the solar wind would cause a reduction in lightning, rather than an increase."[79]

Sunspot "numbers negatively correlate with thunder days in other parts of the world."[79]

"High speed streams were found to occur after periods when the sun was putting out less light, but sunspot numbers increased. Scott and his fellow authors attribute this to the streams coming from an active region appearing on the eastern side of the sun."[79]

"We propose that these particles, while not having sufficient energies to reach the ground and be detected there, nevertheless electrify the atmosphere as they collide with it, altering the electrical properties of the air and thus influencing the rate or intensity at which lightning occurs."[80]

VenusEdit

During the Soviet Venera program, the Venera 11 and Venera 12 probes detected a constant stream of lightning, and Venera 12 recorded a powerful clap of thunder soon after it landed. The European Space Agency's Venus Express recorded abundant lightning in the high atmosphere.[81]

The clouds of Venus are capable of producing lightning much like the clouds on Earth.[82] The existence of lightning had been controversial since the first suspected bursts were detected by the Soviet Venera probes. The lightning rate is at least half of that on Earth.[82] In 2007 the Venus Express probe discovered that a huge double atmospheric vortex exists at the south pole of the planet.[83][84]

During the Soviet Venera program, the Venera 9 orbiter obtained spectroscopic evidence of lightning on Venus,[85] and the Venera 12 descent probe obtained additional evidence of lightning and thunder.[86][87] The European Space Agency's Venus Express in 2007 detected whistler waves further confirming the occurrence of lightning on Venus.[82][81] One possibility is that ash from a volcanic eruption was generating the lightning. Another piece of evidence comes from measurements of sulfur dioxide concentrations in the atmosphere, which dropped by a factor of 10 between 1978 and 1986, jumped in 2006, and again declined 10-fold.[88] This may mean that levels had been boosted several times by large volcanic eruptions.[89][90]

EarthEdit

 
This is a panorama photograph taken during a lightning storm over Bucharest, Romania. Credit: Catalin.Fatu.
 
The image shows multiple lightning discharges. Credit: EL Caballero.
 
Lightning striking the Eiffel Tower, June 3, 1902, at 9:20 P.M. This is one of the earliest photographs of lightning in an urban setting In:"Thunder and Lightning", Camille Flammarion, translated by Walter Mostyn Published in 1906. Credit: M. G. Loppé.{{free media}}
 
This painting of the 1779 eruption of Vesuvius depicts lightning occurring during the eruption. Credit: Michele Torcia, Pierre-Jacques Antoine Volaire, Louis Boilly.

Lightning is an atmospheric discharge of electricity, which typically occurs during thunderstorms, and sometimes during volcanic eruptions or dust storms.

Lightning strikes or bolts across the Earth's sky emit X-rays.[91]

A superbolt, more powerful than an ordinary lightning bolt, struck a cornfield near Leland, Illinois, leaving a crater one foot deep, and breaking windows in homes almost a mile away.[92]

During the 1779 eruption of Vesuvius as depicted in the painting of the right, lightning was observed to strike at or near the column of eruption.

Spatial distributionEdit

 
World map showing frequency of lightning strikes, in flashes per km² per year (equal-area projection), from combined 1995–2003 data from the Optical Transient Detector and 1998–2003 data from the Lightning Imaging Sensor. Credit: Citynoise.

On Earth, the lightning frequency is approximately 44 (± 5) times per second, or nearly 1.4 billion flashes per year[93] and the average duration is 0.2 seconds made up from a number of much shorter flashes (strokes) of around 60 to 70 microseconds.[94]

Lightning hotspots: The place on Earth where lightning occurs most often is near the small village of Kifuka in the mountains of the eastern Democratic Republic of the Congo,[95] where the elevation is around 975 m (3,200 ft). On average, this region receives 158 lightning strikes per 1 square kilometer (0.39 sq mi) per year.[96] Lake Maracaibo in Venezuela averages 297 days per year with lightning activity.[97] Other lightning hotspots include Catatumbo in Venezuela, Singapore,[98] and Lightning Alley in Central Florida.[99][100]

Intra-cloud lightningEdit

 
Flashes of intracloud lightning, the horizontal type shown here, usually occur within clouds high in the atmosphere. Credit: Christoph Laidig, NASA Earth Science Picture of the Day.{{fairuse}}

Lightning discharges may occur between areas of cloud without contacting the ground. When it occurs between two separate clouds it is known as inter-cloud lightning, and when it occurs between areas of differing electric potential within a single cloud it is known as intra-cloud lightning. Intra-cloud lightning is the most frequently occurring type.[40]

Cloud to cloud lightningEdit

 
This image shows a cloud to cloud lightning in a very stormy and rainy night in Zwickau, Germany. Credit: André Karwath.{{free media}}
 
Branching of cloud to cloud lightning, New Delhi, India. Credit: Karthik Easvur.
 
Multiple paths of cloud-to-cloud lightning, Swifts Creek, Victoria, Australia. Credit: Fir0002.
 
Cloud-to-cloud lightning, Victoria, Australia. Credit: Fir0002.
 
Cloud-to-cloud lightning seen in Gresham, Oregon. Credit: JoJoes123.

Lightning discharges may occur between areas of cloud without contacting the ground. When it occurs between two separate clouds it is known as inter-cloud lightning, and when it occurs between areas of differing electric potential within a single cloud it is known as intra-cloud lightning. Intra-cloud lightning is the most frequently occurring type.[40]

Anvil crawler lightningEdit

 
Anvil Crawler over Lake Wright Patman south of Redwater, Texas on the backside of a large area of rain associated with a cold-front. Credit: Griffinstorm.
 
This map shows the largest lightning flash spotted in the satellite data. Credit: Michael Peterson, Los Alamos National Laboratory.{{fairuse}}

Anvil crawler lightning, sometimes called Spider lightning, when leaders propagate through horizontally-extensive charge regions in mature thunderstorms, usually the stratiform regions of mesoscale convective systems, beginning as intracloud discharges originating within the convective region; the negative leader end then propagates well into the aforementioned charge regions in the stratiform area. If the leader becomes too long, it may separate into multiple bidirectional leaders then, the positive end of the separated leader may strike the ground as a positive CG flash or crawl on the underside of the cloud, creating a spectacular display of lightning crawling across the sky. Ground flashes produced in this manner tend to transfer high amounts of charge, and this can trigger upward lightning flashes and upper-atmospheric lightning.[28]

The map on the right "shows the largest lightning flash spotted in the satellite data. Its footprint extended across 44,400 square miles across multiple states. The bar along the bottom shows how the energies and sizes of individual pulses change over time."[101]

Two "record-breaking lightning flashes, the longest by length and by duration [were found in the satellite observations]. One stretched over Brazil some 418 miles from tip to tail—slightly longer than Kansas is across. The second lit up skies for 13.5 seconds over the central United States. A third lightning flash over the southern United States sprawled some 44,400 square miles—nearly the area of Ohio. (Official data aren’t kept for the flash with the largest area, so it's not possible to determine if it set a record.)"[102]

The previous record-holding flashes "called into question our typical view of lightning." But these latest mega-flashes "are now essentially pushing the boundary further for what lightning can be."[101]

The "identification of such large flashes of light demonstrates the power of NOAA’s newest weather satellites, GOES-16 and GOES-17. And the data is a proving ground for [a] new automated processing system, [...] which tackles the most complex lightning data beamed back from space."[102]

"Lightning science is relatively new, and we’re moving basically as quickly as we can get instruments to detect."[103]

The data from these satellites will "give us an opportunity to study lightning in a way we’ve never been able to see before."[103]

Cloud-to-ground lightningEdit

 
Strokes of cloud-to-ground lightning occurred during a thunderstorm. Credit: Mircea Madau.
 
Cloud-to-ground lightning in Maracaibo, Venezuela. Credit: Fox221.
 
A lightning strike from cloud to ground in the California, Mojave Desert. Credit: Jessie Eastland.
 
Cloud to ground lightning is shown. Credit: Yintan.

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 billion joules of energy.[104]

Heat lightningEdit

 
Heat Lightning occurs near Louisville, Kentucky. Credit: Bbadgett.{{free media}}

Heat lightning, sometimes known as silent lightning, 'summer lightning, or dry lightning (mainly used in the American south; not to be confused with dry thunderstorms, which are also often called dry lightning), is a misnomer[105] 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.

Heat lightning is a lightning flash that appears to produce no discernible because it occurs too far away for the thunder to be heard; the sound waves dissipate before they reach the observer.[106]

Dry lightningEdit

 
Cloud to ground lightning strike occurs during a dry thunderstorm near Wagga Wagga, Australia. Credit: Bidgee.

A dry thunderstorm is a thunderstorm that produces thunder and lightning, but most or all of its precipitation evaporates before reaching the ground.[107]

Dry lightning refers to lightning strikes occurring in this situation. Both are so common in the Western United States that they are sometimes used interchangeably.[108] The latter term is a technical misnomer since lightning itself is neither wet nor dry.[108]

Dry thunderstorms occur essentially in dry conditions, and their lightning is a major cause of wildfires.[109][110] Because of that, the National Weather Service, and other agencies around the world, issue forecasts for its likelihood over large areas.[109][111]

Dry lightning is used in Australia, Canada and the United States for lightning that occurs with no precipitation at the surface and is the most common natural cause of wildfires.[112]

Ball lightningEdit

 
The emission spectrum (intensity vs. wavelength) is from a natural ball lightning. Credit: .

Ball lightning may be an atmospheric electrical phenomenon, that refers to reports of luminous, usually spherical objects which vary from pea-sized to several meters in diameter.[113] Ball lightning has been described by eyewitnesses but rarely recorded by meteorologists.[114][115] A wildlife ranger reported taking a photo at Queensland of Australia in 1987.[116]

Recordings were made in July 2012 of the optical spectrum of natural ball lightning during the study of ordinary cloud–ground lightning on the Tibetan Plateau.[117][118] The observed data are consistent with vaporization of soil as well as with ball lightning's sensitivity to electric fields.[117][118][119]

Ribbon lightningEdit

Ribbon lightning occurs in thunderstorms with high cross winds and multiple return strokes, where the wind will blow each successive return stroke slightly to one side of the previous return stroke, causing a ribbon effect.[120]

Rocket lightningEdit

Rocket lightning is a form of cloud discharge, generally horizontal and at cloud base, with a luminous channel appearing to advance through the air with visually resolvable speed, often intermittently.[121]

Staccato lightningEdit

 
This CG was of very short duration, exhibited highly branched channels and was very bright indicating that it was staccato lightning near New Boston, Texas. Credit: Griffinstorm.

Staccato lightning is a cloud-to-ground lightning (CG) strike which is a short-duration stroke that (often but not always) appears as a single very bright flash and often has considerable branching,[122] often found in the visual vault area near the mesocyclone of rotating thunderstorms and coincides with intensification of thunderstorm updrafts, where there is similar cloud-to-cloud strike consisting of a brief flash over a small area, appearing like a blip, also occurs in a similar area of rotating updrafts.[123]

SuperboltsEdit

Superbolts are rather loosely defined as strikes with a peak source power of more than 100 gigawatts (most lightning strikes come in at around 1 gigawatt), which occur about as frequently as one in 240 strikes, not categorically distinct from ordinary lightning strikes, and simply represent the uppermost edge of a continuum, can be either positively or negatively charged, and the charge ratio is comparable to that of "ordinary" lightning. [124][125]

Upward lightningEdit

Upward lightning or ground-to-cloud lightning is a lightning flash which originates from the top of a grounded object and propagates upward from this point, can be triggered by a preceding lightning flash, or it may initiate entirely on its own; where the former is generally found in regions where spider lightning occurs, and may involve multiple grounded objects simultaneously.[126] The latter usually occurs during the cold season and may be the dominant lightning type in thundersnow events.[127]

Bead lightningEdit

Beading of a lightning channel is usually a small-scale feature, and therefore is often only apparent when the observer/camera is close to the lightning.[128]

JupiterEdit

 
Jupiter shows intense X-ray emission associated with auroras in its polar regions (Chandra observatory X-ray image on the left). The accompanying schematic illustrates how Jupiter's unusually frequent and spectacular auroral activity is produced. Observation period: 17 hrs, February 24-26, 2003. Credit: X-ray: NASA/CXC/MSFC/R.Elsner et al.; Illustration: CXC/M.Weiss.

In the image at right is a diagram describing interaction with the local magnetic field. Jupiter's strong, rapidly rotating magnetic field (light blue lines in the figure) generates strong electric fields in the space around the planet. Charged particles (white dots), "trapped in Jupiter's magnetic field, are continually being accelerated (gold particles) down into the atmosphere above the polar regions, so auroras are almost always active on Jupiter. Electric voltages of about 10 million volts, and currents of 10 million amps - a hundred times greater than the most powerful lightning bolts - are required to explain the auroras at Jupiter's poles, which are a thousand times more powerful than those on Earth. On Earth, auroras are triggered by solar storms of energetic particles, which disturb Earth's magnetic field. As shown by the swept-back appearance in the illustration, gusts of particles from the Sun also distort Jupiter's magnetic field, and on occasion produce auroras."[129]

Supporting the idea of water clouds are the flashes of lightning detected in the atmosphere of Jupiter that can be up to a thousand times as powerful as lightning on Earth.[130] The water clouds are assumed to generate thunderstorms in the same way as terrestrial thunderstorms, driven by the heat rising from the interior.[131]

As the spacecraft passed behind the planet, it observed flashes of lightning in the night side atmosphere.[132][133]

SaturnEdit

Starting in early 2005, scientists used Cassini to track lightning on Saturn. The power of the lightning is approximately 1,000 times that of lightning on Earth.[134]

The Radio and Plasma Wave Science instrument (RPWS) on Cassini-Huygens studied the configuration of Saturn's magnetic field and its relationship to Saturn Kilometric Radiation (SKR), as well as monitoring and mapping Saturn's ionosphere, plasma, and lightning from Saturn's (and possibly Titan's) atmosphere.[135][136]

UranusEdit

The extreme pressure and temperature deep within Uranus may break up the methane molecules, with the carbon atoms condensing into crystals of diamond that rain down through the mantle like hailstones.[137][138][139] Very-high-pressure experiments at the Lawrence Livermore National Laboratory suggest that the base of the mantle may comprise an ocean of liquid diamond, with floating solid 'diamond-bergs'.[140][141] Scientists also believe that lightning storms make rainfalls of solid diamonds occur on Uranus, as well as on Jupiter, Saturn, and Neptune.[142][143]

VolcanoesEdit

 
The Villarica volcano erupts near Pucon, Chile, March 3, 2015, with lightning. Credit: Aton Chile/AP Photo.{{fairuse}}
 
The 1995 eruption of Mount Rinjani in Indonesia exhibits volcanic lightning. Credit: Oliver Spalt.{{free media}}
 
The slide depicts a spectacular view of lightning strikes during a third eruption on December 3, 1982. Credit: R. Hadian, U.S. Geological Survey.{{free media}}

On the right is an image of the Villarrica volcano erupting near Pucon, Chile, March 3, 2015, with lightning striking apparently the lower back of the eruption cloud with few leaders.

Many volcanic eruptions put on impressive lightning displays such as during the 1995 eruption of Mount Rinjani in Indonesia shown in the image on the right which exhibits many leaders.

The image on the left shows spectacular lightning strikes around Galunggung, including multiple leaders apparently involved in cloud to cloud lightning.

"This stratovolcano with a lava dome is located in western Java. Its first eruption in 1822 produced a 22-km-long mudflow that killed 4,000 people. The second eruption in 1894 caused extensive property loss. The photo depicts a spectacular view of lightning strikes during a third eruption on December 3, 1982, which resulted in 68 deaths. A fourth eruption occurred in 1984."[144]

Volcanic lightning arises from colliding, fragmenting particles of volcanic ash (and sometimes ice),[145][146] which generate static electricity within the volcanic plume.[147] Volcanic eruptions have been referred to as dirty thunderstorms[148][149] due to moist convection and ice formation that drive the eruption plume dynamics[150][151] and can trigger volcanic lightning.[152][153] But unlike ordinary thunderstorms, volcanic lightning can also occur before any ice crystals have formed in the ash cloud.[154][155]

The earliest recorded observations of volcanic lightning[156] are from Pliny the Younger, describing the eruption of Mount Vesuvius in 79 AD, “There was a most intense darkness rendered more appalling by the fitful gleam of torches at intervals obscured by the transient blaze of lightning.”[157] The first studies of volcanic lightning were also conducted at Mount Vesuvius by Professor Palmieri who observed the eruptions of 1858, 1861, 1868, and 1872 from the Vesuvius Observatory. These eruptions often included lightning activity.[157]

A famous image of the phenomenon was photographed by Carlos Gutierrez and occurred in Chile above the Chaiten Volcano.[158] It circulated widely on the internet. Another notable image of this phenomenon is "The Power of Nature",[159] taken by Mexican photographer Sergio Tapiro[160] in Colima, Mexico, which won third place (Nature category) in the 2016 World Press Photo Contest.[161] Other instances have been reported above Alaska's Mount Augustine volcano,[162] Iceland's 2010 eruptions of Eyjafjallajökull volcano[163] and Mount Etna in Sicily, Italy.[164]

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