Lightning

Not to be confused with Lighting.
For other uses, see Lightning (disambiguation).
"Return stroke" redirects here. For other uses, see Return stroke (disambiguation).
A lightning flash during a thunderstorm
Sound of a thunderstorm
High-speed, slow-motion lightning video captured at 6,200 frames per second.
Four-second video of a lightning strike, Island in the Sky, Canyonlands National Park, Utah, United States.

Lightning is a sudden electrostatic discharge during an electrical storm between electrically charged regions of a cloud (called intra-cloud lightning or IC), between that cloud and another cloud (CC lightning), or between a cloud and the ground (CG lightning). The charged regions in the atmosphere temporarily equalize themselves through this discharge referred to as a strike if it hits an object on the ground, and a flash if it occurs within a cloud. Lightning causes light in the form of plasma, and sound in the form of thunder. Lightning may be seen and not heard when it occurs at a distance too great for the sound to carry as far as the light from the strike or flash.

General considerations

On Earth, the lightning frequency is approximately 40–50 times a second or nearly 1.4 billion flashes per year[1] and the average duration is 0.2 seconds made up from a number of much shorter flashes (strokes) of around 30 microseconds.[2]

Many factors affect the frequency, distribution, strength and physical properties of a "typical" lightning flash in a particular region of the world. These factors include ground elevation, latitude, prevailing wind currents, relative humidity, proximity to warm and cold bodies of water, etc. To a certain degree, the ratio between IC, CC and CG lightning may also vary by season in middle latitudes. Because human beings are terrestrial and most of their possessions are on the Earth, where lightning can damage or destroy them, CG lightning is the most studied and best understood of the three types, even though IC and CC are more common types of lightning. Lightning's relative unpredictability limits a complete explanation of how or why it occurs, even after hundreds of years of scientific investigation.

A typical cloud to ground lightning flash culminates in the formation of an electrically conducting plasma channel through the air in excess of 5 kilometres (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.[3] At its peak, a typical thunderstorm produces three or more strikes to the Earth per minute.[4] Lightning primarily occurs when warm air is mixed with colder air masses, resulting in atmospheric disturbances necessary for polarizing the atmosphere. 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.[5][6] Hurricanes typically generate some lightning, mainly in the rainbands as much as 160 kilometres (99 mi) from the center.[7][8][9]

The science of lightning is called fulminology, and the fear of lightning is called astraphobia.

Frequency

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.

Lightning is not distributed evenly around the planet, as shown in the map.

About 70% of lightning occurs over land in the tropics where atmospheric convection is the greatest. This occurs from both the mixture of warmer and colder air masses, as well as differences in moisture concentrations, and it generally happens at the boundaries between them. The flow of warm ocean currents past drier land masses, such as the Gulf Stream, partially explains the elevated frequency of lightning in the Southeast United States. Because the influence of small or absent land masses in the vast stretches of the world's oceans limits the differences between these variants in the atmosphere, lightning is notably less frequent there than over larger landforms. The North and South Poles are limited in their coverage of thunderstorms and therefore result in areas with the least amount of lightning.

In general, cloud-to-ground (CG) lightning flashes account for only 25% of all total lightning flashes worldwide. Since the base of a thunderstorm is usually negatively charged, this is where most CG lightning originates. This region is typically at the elevation where freezing occurs within the cloud. Freezing, combined with collisions between ice and water, appears to be a critical part of the initial charge development and separation process. During wind-driven collisions, ice crystals tend to develop a positive charge, while a heavier, slushy mixture of ice and water (called graupel) develops a negative charge. Updrafts within a storm cloud separate the lighter ice crystals from the heavier graupel, causing the top region of the cloud to accumulate a positive space charge while the lower level accumulates a negative space charge.

Lightning in Belfort, France

Because the concentrated charge within the cloud must exceed the insulating properties of air, and this increases proportionally to the distance between the cloud and the ground, the proportion of CG strikes (versus cloud-to-cloud (CC) or in-cloud (IC) discharges) becomes greater when the cloud is closer to the ground. In the tropics, where the freezing level is generally higher in the atmosphere, only 10% of lightning flashes are CG. At the latitude of Norway (around 60° North latitude), where the freezing elevation is lower, 50% of lightning is CG.[10][11]

Lightning is usually produced by cumulonimbus clouds, which have bases that are typically 1–2 km (0.6-1.25 miles) above the ground and tops up to 15 km (9.3 mi) in height.

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,[12] 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.[13] Lake Maracaibo in Venezuela averages 297 days per year with lightning activity. [14] Other lightning hotspots include Catatumbo in Venezuela, Singapore,[15] Teresina in northern Brazil,[16] and Lightning Alley in Central Florida.[17][18]

Necessary conditions

Main article: Thunderstorm

In order for an electrostatic discharge to occur, two preconditions are necessary: (1) a sufficiently high electric potential between two regions of space must exist; and (2) a high-resistance medium must obstruct the free, unimpeded equalization of the opposite charges.

It is well understood that during a thunderstorm there is charge separation and aggregation in certain regions of the cloud; however the exact processes by which this occurs are not fully understood.[19]

The atmosphere provides the electrical insulation, or barrier, that prevents free equalization between charged regions of opposite polarity. This is overcome by "lightning", a complex process referred to as the lightning "flash".

Electrical field generation

View of lightning from an airplane flying above a system.

As a thundercloud moves over the surface of the Earth, an equal electric charge, but of opposite polarity, is induced on the Earth's surface underneath the cloud. The induced positive surface charge, when measured against a fixed point, will be small as the thundercloud approaches, increasing as the center of the storm arrives and dropping as the thundercloud passes. The referential value of the induced surface charge could be roughly represented as a bell curve.

The oppositely charged regions create an electric field within the air between them. This electric field varies in relation to the strength of the surface charge on the base of the thundercloud – the greater the accumulated charge, the higher the electrical field.

Flashes and strikes

The best studied and understood form of lightning is cloud to ground (CG). Although more common, intracloud (IC) and cloud to cloud (CC) flashes are very difficult to study given there are no "physical" points to monitor inside the clouds. Also, given the very low probability lightning will strike the same point repeatedly and consistently, scientific inquiry is difficult at best even in the areas of high CG frequency. As such, knowing flash propagation is similar amongst all forms of lightning, the best means to describe the process is through an examination of the most studied form, cloud to ground.

A lightning strike from cloud to ground in the California, Mojave Desert
An intracloud flash. A lightning flash within the cloud, illuminates the entire blanket.

Downward leaders

A downward leader travels towards earth, branching as it goes.
Lightning strike caused by the connection of two leaders, positive shown in blue and negative in red

In a process not well understood, a channel of ionized air, called a "leader", is initiated from a charged region in the thundercloud. Leaders are electrically conductive channels of partially ionized gas that travel away from a region of dense charge. Negative leaders propagate away from densely charged regions of negative charge, and positive leaders propagate from positively charged regions.

The positively and negatively charged leaders proceed in opposite directions, positive upwards within the cloud and negative towards the earth. Both ionic channels proceed, in their respective directions, in a number of successive spurts. Each leader "pools" ions at the leading tips, shooting out one or more new leaders, momentarily pooling again to concentrate charged ions, then shooting out another leader.

Leaders often split, forming branches in a tree-like pattern.[20] In addition, negative leaders travel in a discontinuous fashion. The resulting jerky movement of these "stepped leader(s)" can be readily observed in slow-motion videos of negative leaders as they head toward ground prior to a negative CG lightning strike. The negative leaders continue to propagate and split as they head downward, often speeding up as they get closer to the Earth's surface.

About 90% of ionic channel lengths between "pools" are approximately 45 m (148 ft) in length.[21] The establishment of the ionic channel takes a comparatively long amount of time (hundreds of milliseconds) in comparison to resulting discharge which occurs within a few microseconds. The electric current needed to establish the channel, measured in the tens or hundreds of amperes, is dwarfed by subsequent currents during the actual discharge.

Initiation of the outward leaders is not well understood. The electric field strength within the thundercloud is not typically large enough to initiate this process by itself.[22] Many hypotheses have been proposed. One theory postulates that showers of relativistic electrons are created by cosmic rays and are then accelerated to higher velocities via a process called runaway breakdown. As these relativistic electrons collide and ionize neutral air molecules, they initiate leader formation. Another theory invokes locally enhanced electric fields being formed near elongated water droplets or ice crystals.[23] Percolation theory, especially for the case of biased percolation,[24] describes random connectivity phenomena, which produce an evolution of connected structures similar to that of lightning strikes.

Upward streamers

When a stepped leader approaches the ground, the presence of opposite charges on the ground enhances the strength of the electric field. The electric field is strongest on grounded objects whose tops are closest to the base of the thundercloud, such as trees and tall buildings. If the electric field is strong enough, a positively charged ionic channel, called a positive or upward streamer, can develop from these points. This was first theorized by Heinz Kasemir.[25][26]

As negatively charged leaders approach, increasing the localized electric field strength, grounded objects already experiencing corona discharge exceed a threshold and form upward streamers.

Attachment

Once a downward leader connects to an available upward leader, a process referred to as attachment, a low-resistance path is formed and discharge may occur. Photographs have been taken on which unattached streamers are clearly visible. The unattached downward leaders are also visible in branched lightning, none of which are connected to the earth, although it may appear they are.[27]

Discharge

Return stroke

High-speed photography showing different parts of a lightning flash during the discharge process as seen in Toulouse, France.

Once a conductive channel bridges the air gap between the negative charge excess in the cloud and the positive surface charge excess below, a massive electrical discharge follows. This is the 'return stroke' and it is the most luminous and noticeable part of the lightning discharge.

A large electron current flows along the plasma channel from the cloud to the ground, neutralising the positive ground charge as electrons flow away from the strike point to the surrounding area. This huge surge of current creates large radial voltage differences along the surface of the ground. Called step potentials, they are responsible for more injuries and deaths than the strike itself. Electricity takes every path available to it.[28] A portion of the return stroke current will often preferentially flow through one leg and out another, electrocuting an unlucky human or animal standing near the point where the lightning strikes.

The electric current of the return stroke averages 30 kiloamperes for a typical negative CG flash, often referred to as "negative CG" lightning. In some cases, a positive ground to cloud (GC) lightning flash may originate from a positively charged region on the ground below a storm. These discharges normally originate from the tops of very tall structures, such as communications antennas. The rate at which the return stroke current travels has been found to be around 1×108 m/s.[29]

The massive flow of electric current occurring during the return stroke combined with the rate at which it occurs (measured in microseconds) rapidly superheats the completed leader channel, forming a highly electrically conductive plasma channel. The core temperature of the plasma during the return stroke may exceed 50,000 K, causing it to brilliantly radiate with a blue-white color. Once the electric current stops flowing, the channel cools and dissipates over tens or hundreds of milliseconds, often disappearing as fragmented patches of glowing gas. The nearly instantaneous heating during the return stroke causes the air to explosively expand, producing a powerful shock wave that is heard as thunder.

Re-strike

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.[30]

Each re-strike is separated by a relatively large amount of time, typically 40 to 50 milliseconds, as other charged regions in the cloud are discharged in subsequent strokes. Re-strikes often cause a noticeable "strobe light" effect.[31]

Each successive stroke is preceded by intermediate dart leader strokes that have a faster rise time but lower amplitude than the initial return stroke. Each subsequent stroke usually re-uses the discharge channel taken by the previous one, but the channel may be offset from its previous position as wind displaces the hot channel.[32]

Transient currents during flash

The electric current within a typical negative CG lightning discharge rises very quickly to its peak value in 1–10 microseconds, then decays more slowly over 50–200 microseconds. The transient nature of the current within a lightning flash results in several phenomena that need to be addressed in the effective protection of ground-based structures. Rapidly changing currents tend to travel on the surface of a conductor. This is called skin effect, unlike direct currents "flowing through" the entire conductor like water through a hose. Hence, conductors used in the protection of facilities tend to be multi-stranded small wires woven together, that increases the surface area inversely in proportion to cross-sectional area.

The rapidly changing currents also create electromagnetic pulses (EMPs) that radiate outward from the ionic channel. This is a characteristic of all electrical sparks. The radiated pulses rapidly weaken as their distance from the origin increases. However, if they pass over conductive elements, for instance electrical wires, communication lines or metallic pipes, they may induce a current which travels outward to its termination. This is the "surge" that, more often than not, results in the destruction of delicate electronics, electrical appliances or electric motors. Devices known as surge protectors (SPD) or transient voltage surge suppressors (TVSS) attached in parallel with these lines can detect the lightning flash's transient [irregular] current, and through an alteration of its physical properties, route the spike to an attached earthing ground, thereby protecting the equipment from damage.

Types

There are three primary types of lightning, defined by what is at the "ends" of a flash channel. They are intracloud (IC), which occurs within a single thundercloud unit; cloud to cloud (CC), which starts and ends between two different "functional" thundercloud units; and cloud to ground (CG), that primarily originates in the thundercloud and terminates on an Earth surface, but may also occur in the reverse direction, that is ground to cloud. There are variations of each type, such as "positive" versus "negative" CG flashes, that have different physical characteristics common to each which can be measured. Different common names used to describe a particular lightning event may be attributed to the same or different events.

Cloud to ground (CG)

Cloud-to-ground is the best known and third most common type of lightning. It is the best understood of all forms because it allows for scientific study given it terminates on a physical object, namely the Earth, and lends itself to being measured by instruments. Of the three primary types of lightning, it poses the greatest threat to life and property since it terminates or "strikes" the Earth. Cloud-to-ground (CG) lightning is a lightning discharge between a thundercloud and the ground. It is usually negative in polarity and is usually initiated by a stepped leader moving down from the cloud.

Positive and negative lightning

CG lightning can occur with both positive and negative polarity. The polarity is that of the charge in the region that originated the lightning leaders. An average bolt of negative lightning carries an electric current of 30,000 amperes (30 kA), and transfers 15 coulombs of electric charge and 500 megajoules of energy. Large bolts of lightning can carry up to 120 kA and 350 coulombs.[33]

Anvil-to-ground (Bolt from the blue) lightning strike initiates from the clear, but turbulent sky above the cloud, then drives a Plasma anvil through the cloud directly to the ground.

Unlike the far more common "negative" lightning, positive lightning originates from the positively charged top of the clouds (generally anvil clouds) rather than the lower portion of the storm. Leaders form in the anvil of the cumulonimbus and may travel horizontally for several miles before veering towards the ground. A positive lightning bolt can strike anywhere within several miles of the anvil of the thunderstorm, often in areas experiencing clear or only slightly cloudy skies; they are also known as "bolts from the blue" for this reason. Positive lightning typically makes up less than 5% of all lightning strikes.[34]

Because of the much greater distance to ground, the positively charged region can develop considerably larger levels of charge and voltages than the negative charge regions in the lower part of the cloud. Positive lightning bolts are considerably hotter and longer than negative lightning. They can develop six to ten times the amount of charge and voltage of a negative bolt and the discharge current may last ten times longer.[35] A bolt of positive lightning may carry an electric current of 300 kA and the potential at the top of the cloud may exceed a billion volts — about 10 times that of negative lightning.[36] During a positive lightning strike, huge quantities of extremely low frequency (ELF) and very low frequency (VLF) radio waves are generated.[37]

As a result of their greater power, as well as lack of warning, positive lightning strikes are considerably more dangerous. At the present time, aircraft are not designed to withstand such strikes, since their existence was unknown at the time standards were set, and the dangers unappreciated until the destruction of a glider in 1999.[38] The standard in force at the time of the crash, Advisory Circular AC 20-53A, was replaced by Advisory Circular AC 20-53B in 2006,[39] however it is unclear whether adequate protection against positive lightning was incorporated.[40][41]

Aircraft operating in U.S. airspace have been required to be equipped with static discharge wicks. Although their primary function is to mitigate radio interference due to static buildup through friction with the air, in the event of a lightning strike, a plane is designed to conduct the excess electricity through its skin and structure to the wicks to be safely discharged back into the atmosphere. These measures, however, may be insufficient for positive lightning.[42]

Positive lightning has also been shown to trigger the occurrence of Upper-atmospheric lightning between the tops of clouds and the ionosphere. Positive lightning tends to occur more frequently in winter storms, as with thundersnow, and in the dissipation stage of a thunderstorm.[43]

Cloud to cloud (CC) and intra-cloud (IC)

Branching of cloud to cloud lightning, New Delhi, India
Multiple paths of cloud-to-cloud lightning, Swifts Creek, Australia.
Cloud-to-cloud lightning, Victoria, Australia.
Cloud-to-cloud lightning seen in Gresham, Oregon.

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.[43]

Intra-cloud lightning most commonly occurs between the upper anvil portion and lower reaches of a given thunderstorm. This lightning can sometimes be observed at great distances at night as so-called "heat lightning". In such instances, the observer may see only a flash of light without hearing any thunder.

Anvil Crawler over Lake Wright Patman south of Redwater, Texas on the backside of a large area of rain associated with a cold-front

Another term used for cloud–cloud or cloud–cloud–ground lightning is "Anvil Crawler", due to the habit of charge, typically originating beneath or within the anvil and scrambling through the upper cloud layers of a thunderstorm, often generating dramatic multiple branch strokes. These are usually seen as a thunderstorm passes over the observer or begins to decay. The most vivid crawler behavior occurs in well developed thunderstorms that feature extensive rear anvil shearing.

Observational variations

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.

Effects

Lightning strike

Main article: Lightning strike

Objects struck by lightning experience heat and magnetic forces of great magnitude. The heat created by lightning currents traveling through a tree may vaporize its sap, causing a steam explosion that bursts the trunk. As lightning travels through sandy soil, the soil surrounding the plasma channel may melt, forming tubular structures called fulgurites. Even though roughly 90 percent of people struck by lightning survive,[57] humans or animals struck by lightning may suffer severe injury due to internal organ and nervous system damage. Buildings or tall structures hit by lightning may be damaged as the lightning seeks unintended paths to ground. By safely conducting a lightning strike to ground, a lightning protection system can greatly reduce the probability of severe property damage. Lightning also oxidizes nitrogen in the air into nitrates which are deposited by rain and can fertilize plant growth.[58][59]

Thunder

Main article: Thunder

Because the electrostatic discharge of terrestrial lightning superheats the air to plasma temperatures along the length of the discharge channel in a short duration, kinetic theory dictates gaseous molecules undergo a rapid increase in pressure and thus expand outward from the lightning creating a shock wave audible as thunder. Since the sound waves propagate not from a single point source but along the length of the lightning's path, the sound origin's varying distances from the observer can generate a rolling or rumbling effect. Perception of the sonic characteristics is further complicated by factors such as the irregular and possibly branching geometry of the lightning channel, by acoustic echoing from terrain, and by the typically multiple-stroke characteristic of the lightning strike.

Light travels at about 300,000,000 m/s, and sound travels through air at about 340 m/s. An observer can approximate the distance to the strike by timing the interval between the visible lightning and the audible thunder it generates. A lightning flash preceding its thunder by one second would be approximately 350 metres (0.22 mi) in distance; a delay of three seconds would indicate a distance of about one kilometer (0.62 mi) (3×340 m). A flash preceding thunder by five seconds would indicate a distance of approximately one mile (1.6 km) (5×340 m). Consequently, a lightning strike observed at a very close distance will be accompanied by a sudden clap of thunder, with almost no perceptible time lapse, possibly accompanied by the smell of ozone (O3).

High-energy radiation

The production of X-rays by a bolt of lightning was theoretically predicted as early as 1925[60] but no evidence was found until 2001/2002,[61][62][63] when researchers at the New Mexico Institute of Mining and Technology detected X-ray emissions from an induced lightning strike along a grounded wire trailed behind a rocket shot into a storm cloud. In the same year University of Florida and Florida Tech researchers used an array of electric field and X-ray detectors at a lightning research facility in North Florida to confirm that natural lightning makes X-rays in large quantities during the propagation of stepped leaders. The cause of the X-ray emissions is still a matter for research, as the temperature of lightning is too low to account for the X-rays observed.[64][65]

A number of observations by space-based telescopes have revealed even higher energy gamma ray emissions, the so-called terrestrial gamma-ray flashes (TGFs). These observations pose a challenge to current theories of lightning, especially with the recent discovery of the clear signatures of antimatter produced in lightning.[66]

Volcanic

Volcanic material thrust high into the atmosphere can trigger lightning.

Volcanic activity produces lightning-friendly conditions in multiple ways. The enormous quantity of pulverized material and gases ejected into the atmosphere with explosive power, creates a dense plume of highly charged particles, which establishes the perfect conditions for lightning. The ash density and constant motion within the volcanic plume continually produces electrostatic ionization, resulting in very powerful and very frequent flashes attempting to neutralize itself. Due to the extensive solid material (ash) content, unlike the water rich charge generating zones of a normal thundercloud, it is often called a dirty thunderstorm.

Extraterrestrial

Lightning has been observed within the atmospheres of other planets, such as Venus, Jupiter and Saturn. Although in the minority on Earth, superbolts appear to be common on Jupiter.

Lightning on Venus has been a controversial subject after decades of study. During the Soviet Venera and U.S. Pioneer missions of the 1970s and 1980s, signals suggesting lightning may be present in the upper atmosphere were detected.[69] Although the Cassini–Huygens mission fly-by of Venus in 1999 detected no signs of lightning, the observation window lasted mere hours. Radio pulses recorded by the spacecraft Venus Express (which began orbiting Venus in April 2006) have been confirmed as originating from lightning on Venus.

Human-related phenomena

Scientific study

Properties

Thunder is heard as a rolling, gradually dissipating rumble because the sound from different portions of a long stroke arrives at slightly different times.[72]

When the local electric field exceeds the dielectric strength of damp air (about 3 million volts per meter), electrical discharge results in a strike, often followed by commensurate discharges branching from the same path. (See image, right.) Mechanisms that cause the charges to build up to lightning are still a matter of scientific investigation.[73][74] New study confirming dielectric breakdown is involved. Rison 2016. Lightning may be caused by the circulation of warm moisture-filled air through electric fields.[75] Ice or water particles then accumulate charge as in a Van de Graaff generator.[76]

Researchers at the University of Florida found that the final one-dimensional speeds of 10 flashes observed were between 1.0×105 and 1.4×106 m/s, with an average of 4.4×105 m/s.[77]

Detection and monitoring

Ray counter in a museum.
Main article: Lightning detection

The earliest detector invented to warn of the approach of a thunder storm was the lightning bell. Benjamin Franklin installed one such device in his house.[78] [79] The detector was based on an electrostatic device called the 'electric chimes' invented by Andrew Gordon in 1742.

Lightning discharges generate a wide range of electromagnetic radiations, including radio-frequency pulses. The times at which a pulse from a given lightning discharge arrives at several receivers can be used to locate the source of the discharge. The United States federal government has constructed a nationwide grid of such lightning detectors, allowing lightning discharges to be tracked in real time throughout the continental U.S.[80][81]

The Earth-ionosphere waveguide traps electromagnetic VLF- and ELF waves. Electromagnetic pulses transmitted by lightning strikes propagate within that waveguide. The waveguide is dispersive, which means that their group velocity depends on frequency. The difference of the group time delay of a lightning pulse at adjacent frequencies is proportional to the distance between transmitter and receiver. Together with direction finding methods, this allows to locate lightning strikes up to distances of 10000 km from their origin. Moreover, the eigenfrequencies of the Earth-ionospheric waveguide, the Schumann resonances at about 7.5 Hz, are used to determine the global thunderstorm activity.[82]

In addition to ground-based lightning detection, several instruments aboard satellites have been constructed to observe lightning distribution. These include the Optical Transient Detector (OTD), aboard the OrbView-1 satellite launched on April 3, 1995, and the subsequent Lightning Imaging Sensor (LIS) aboard TRMM launched on November 28, 1997.[83][84][85]

Artificially triggered

Physical manifestations

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

Magnetism

The movement of electrical charges produces a magnetic field (see electromagnetism). The intense currents of a lightning discharge create a fleeting but very strong magnetic field. Where the lightning current path passes through rock, soil, or metal these materials can become permanently magnetized. This effect is known as lightning-induced remanent magnetism, or LIRM. These currents follow the least resistive path, often horizontally near the surface[100][101] but sometimes vertically, where faults, ore bodies, or ground water offers a less resistive path.[102] One theory suggests that lodestones, natural magnets encountered in ancient times, were created in this manner.[103]

Lightning-induced magnetic anomalies can be mapped in the ground,[104][105] and analysis of magnetized materials can confirm lightning was the source of the magnetization[106] and provide an estimate of the peak current of the lightning discharge.[107]

Solar wind and cosmic rays

Some high energy cosmic rays produced by supernovas as well as solar particles from the solar wind, enter the atmosphere and electrify the air, creating pathways for lightning bolts.[108]

In culture and religion

Further information: Lightning in religion
Lightning by Mikalojus Konstantinas Ciurlionis (1909)

In many cultures, lightning has been viewed as part of a deity or a deity in and of itself. These include the Greek god Zeus, the Aztec god Tlaloc, the Mayan God K, Slavic mythology's Perun, the Baltic Pērkons/Perkūnas, Thor in Norse mythology, Ukko in Finnish mythology, the Hindu god Indra, and the Shinto god Raijin.[109] In the traditional religion of the African Bantu tribes, lightning is a sign of the ire of the gods. Verses in the Jewish religion and in Islam also ascribe supernatural importance to lightning. In Christianity, the Second Coming of Jesus is compared to lightning.[Matthew 24:27][Luke 17:24]

The expression "Lightning never strikes twice (in the same place)" is similar to "Opportunity never knocks twice" in the vein of a "once in a lifetime" opportunity, i.e., something that is generally considered improbable. Lightning occurs frequently and more so in specific areas. Since various factors alter the probability of strikes at any given location, repeat lightning strikes have a very low probability (but are not impossible).[110][111] Similarly, "A bolt from the blue" refers to something totally unexpected.

Some political parties use lightning flashes as a symbol of power, such as the People's Action Party in Singapore, the British Union of Fascists during the 1930s, and the National States' Rights Party in the United States during the 1950s.[112] The Schutzstaffel, the paramilitary wing of the Nazi Party, used the Sig rune in their logo which symbolizes lightning. The German word Blitzkrieg, which means "lightning war", was a major offensive strategy of the German army during World War II.

In French and Italian, the expression for "Love at first sight" is coup de foudre and colpo di fulmine, respectively, which literally translated means "lightning strike". Some European languages have a separate word for lightning which strikes the ground (as opposed to lightning in general); often it is a cognate of the English word "rays". The name of New Zealand's most celebrated thoroughbred horse, Phar Lap, derives from the shared Zhuang and Thai word for lightning.[113]

The bolt of lightning in heraldry is called a thunderbolt and is shown as a zigzag with non-pointed ends. This symbol usually represents power and speed.

The lightning bolt is used to represent the instantaneous communication capabilities of electrically powered telegraphs and radios. It was a commonly used motif in Art Deco design, especially the zig-zag Art Deco design of the late 1920s.[114] The lightning bolt is a common insignia for military communications units throughout the world. A lightning bolt is also the NATO symbol for a signal asset.

The Unicode symbol for lightning is ☇ U+2607

See also

References

Notes

  1. ↑ Oliver, John E. (2005). Encyclopedia of World Climatology. National Oceanic and Atmospheric Administration. ISBN 978-1-4020-3264-6. Retrieved February 8, 2009.
  2. ↑ "Lightning". gsu.edu. Retrieved December 30, 2015.
  3. ↑ Uman (1986) p. 81.
  4. ↑ Uman (1986) p. 55.
  5. ↑ New Lightning Type Found Over Volcano?. News.nationalgeographic.com (February 2010). Retrieved on June 23, 2012.
  6. ↑ "Bench collapse sparks lightning, roiling clouds". Volcano Watch. United States Geological Survey. June 11, 1998. Retrieved October 7, 2012.
  7. ↑ Pardo-Rodriguez, Lumari (Summer 2009) Lightning Activity in Atlantic Tropical Cyclones: Using the Long-Range Lightning Detection Network (LLDN). MA Climate and Society, Columbia University Significant Opportunities in Atmospheric Research and Science Program.
  8. ↑ Hurricane Lightning, NASA, January 9, 2006.
  9. ↑ The Promise of Long-Range Lightning Detection in Better Understanding, Nowcasting, and Forecasting of Maritime Storms. Long Range Lightning Detection Network
  10. ↑ "Where LightningStrikes". NASA Science. Science News. December 5, 2001. Retrieved July 5, 2010.
  11. ↑ Uman (1986) Ch. 8, p. 68.
  12. ↑ "Kifuka – place where lightning strikes most often". Wondermondo. Retrieved November 21, 2010.
  13. ↑ "Annual Lightning Flash Rate". National Oceanic and Atmospheric Administration. Archived from the original on March 30, 2008. Retrieved February 8, 2009.
  14. ↑ Fischetti, M. (2016) Lightning Hotspots, Scientific American 314: 76 (May 2016)
  15. ↑ "Lightning Activity in Singapore". National Environmental Agency. 2002. Archived from the original on 2007-09-27. Retrieved September 24, 2007.
  16. ↑ "Teresina: Vacations and Tourism". Paesi Online. Archived from the original on September 5, 2008. Retrieved September 24, 2007.
  17. ↑ "Staying Safe in Lightning Alley". NASA. January 3, 2007. Retrieved September 24, 2007.
  18. ↑ Pierce, Kevin (2000). "Summer Lightning Ahead". Florida Environment.com. Retrieved September 24, 2007.
  19. ↑ Saunders, C. P. R. (1993). "A Review of Thunderstorm Electrification Processes". Journal of Applied Meteorology 32 (4): 642. Bibcode:1993JApMe..32..642S. doi:10.1175/1520-0450(1993)032<0642:AROTEP>2.0.CO;2.
  20. ↑ Ultraslow-motion video of stepped leader propagation: ztresearch.com
  21. ↑ Goulde, R.H. (1977) "The lightning conductor", pp. 545–576 in Lightning Protection, R.H. Golde, Ed., Lightning, Vol. 2, Academic Press.
  22. ↑ Stolzenburg, Maribeth; Marshall, Thomas C. (2008). "Charge Structure and Dynamics in Thunderstorms". Space Science Reviews 137: 355. Bibcode:2008SSRv..137..355S. doi:10.1007/s11214-008-9338-z.
  23. ↑ Petersen, Danyal; Bailey, Matthew; Beasley, William H.; Hallett, John (2008). "A brief review of the problem of lightning initiation and a hypothesis of initial lightning leader formation". Journal of Geophysical Research 113. Bibcode:2008JGRD..11317205P. doi:10.1029/2007JD009036.
  24. ↑ Hooyberghs, Hans; Van Schaeybroeck, Bert; Moreira, André A.; Andrade, José S.; Herrmann, Hans J.; Indekeu, Joseph O. (2010). "Biased percolation on scale-free networks". Physical Review E 81. arXiv:0908.3786. Bibcode:2010PhRvE..81a1102H. doi:10.1103/PhysRevE.81.011102.
  25. ↑ Kasemir, H. W. (1950) "Qualitative Übersicht über Potential-, Feld- und Ladungsverhaltnisse bei einer Blitzentladung in der Gewitterwolke" (Qualitative survey of the potential, field and charge conditions during a lightning discharge in the thunderstorm cloud) in Das Gewitter (The Thunderstorm), H. Israel, ed., Leipzig, Germany: Akademische Verlagsgesellschaft.
  26. ↑ Ruhnke, Lothar H. (June 7, 2007) Death notice: Heinz Wolfram Kasemir. physicstoday.org
  27. ↑ File:Lightning hits tree.jpg
  28. ↑ "The Path of Least Resistance".
  29. ↑ Idone, V. P.; Orville, R. E.; Mach, D. M.; Rust, W. D. (1987). "The propagation speed of a positive lightning return stroke". Geophysical Research Letters 14 (11): 1150. Bibcode:1987GeoRL..14.1150I. doi:10.1029/GL014i011p01150.
  30. ↑ Uman (1986) Ch. 5, p. 41.
  31. ↑ Uman (1986) pp. 103–110.
  32. ↑ Uman (1986) Ch. 9, p. 78.
  33. ↑ Hasbrouck, Richard. Mitigating Lightning Hazards, Science & Technology Review May 1996. Retrieved on April 26, 2009.
  34. ↑ "NWS JetStream – The Positive and Negative Side of Lightning". National Oceanic and Atmospheric Administration. Retrieved September 25, 2007.
  35. ↑ Lawrence, D (November 1, 2005). "Bolt from the Blue". National Oceanic and Atmospheric Administration. Archived from the original on May 14, 2009. Retrieved August 20, 2009.
  36. ↑ The Positive and Negative Side of Lightning, National Weather Service JetStream January 2010. Retrieved on June 11, 2011.
  37. ↑ Boccippio, DJ; Williams, ER; Heckman, SJ; Lyons, WA; Baker, IT; Boldi, R (August 1995). "Sprites, ELF Transients, and Positive Ground Strokes". Science 269 (5227): 1088–1091. Bibcode:1995Sci...269.1088B. doi:10.1126/science.269.5227.1088. PMID 17755531.
  38. ↑ "Air Accidents Investigation Branch (AAIB) Bulletins 1999 December: Schleicher ASK 21 two seat glider". Retrieved May 17, 2015.
  39. ↑ FAA Advisory Circulars. Airweb.faa.gov. Retrieved on June 23, 2012.
  40. ↑ Hiding requirements = suspicion they're inadequate, Nolan Law Group, January 18, 2010
  41. ↑ A Proposed Addition to the Lightning Environment Standards Applicable to Aircraft, J. Anderson Plumer Lightning Technologies, Inc, published September 27, 2005
  42. ↑ Ask Us – Static Discharge Wicks. Aerospaceweb.org (June 26, 2005). Retrieved on June 23, 2012.
  43. 1 2 Christian, Hugh J. and McCook, Melanie A. "A Lightning Primer – Characteristics of a Storm". NASA. Retrieved February 8, 2009.
  44. ↑ Singer, Stanley (1971). The Nature of Ball Lightning. New York: Plenum Press. ISBN 978-0-306-30494-1.
  45. ↑ Ball, Philip (January 17, 2014). "Focus:First Spectrum of Ball Lightning". Focus. American Physical Society. Retrieved January 18, 2014.
  46. ↑ Tennakone, Kirthi (2007). "Ball Lightning". Georgia State University. Retrieved September 21, 2007.
  47. ↑ Porter, Brett (1987). "Brett Porter, Photo in 1987, BBC:Ball lightning baffles scientists, day, 21 December, 2001, 00:26 GMT".
  48. ↑ Robinson, Dan. "Weather Library: Lightning Types & Classifications". Retrieved March 17, 2013.
  49. ↑ Scott, A (2000). "The Pre-Quaternary history of fire". Palaeogeography Palaeoclimatology Palaeoecology 164 (1–4): 281. doi:10.1016/S0031-0182(00)00192-9.
  50. ↑ Haby, Jeff. "What is heat lightning?". theweatherprediction.com.
  51. ↑ "Definition of Rocket Lightning, AMS Glossary of Meteorology". Retrieved July 5, 2007.
  52. ↑ "Glossary". National Oceanic and Atmospheric Administration. National Weather Service. Retrieved September 2, 2008.
  53. ↑ Marshall, Tim; David Hoadley (illustrator) (May 1995). Storm Talk. Texas.
  54. ↑ "Detection of lightning superbolts". wiley.com. Retrieved December 30, 2015.
  55. ↑ http://www.forte.lanl.gov/science/publications/1999/Kirkland_1999_1_Examination.pdf
  56. ↑ "When Lightning Strikes Out of a Blue Sky". DNews. Retrieved October 15, 2015.
  57. ↑ Jabr, Ferris (22 September 2014). "Lightning-Strike Survivors Tell Their Stories". Outside. Retrieved 28 September 2014.
  58. ↑ Bond, D.W., Steiger, S., Zhang, R., Tie, X., Orville, R.E. 2002. The importance of NOx production by lightning in the tropics. Atmospheric Environment 36:1509–1519.
  59. ↑ Pickering, K.E., Bucsela, E., Allen, D, Cummings, K., Li, Y., MacGorman, D., Bruning, E. 2014. Estimates of Lightning NOx Production Per Flash from OMI NO2 and Lightning Observations. XV International Conference on Atmospheric Electricity, 15-20, June 2014.
  60. ↑ Wilson, C.T.R. (1925). "The acceleration of beta-particles in strong electric fields such as those of thunderclouds". Proceedings of the Cambridge Philosophical Society 22 (4): 534–538. Bibcode:1925PCPS...22..534W. doi:10.1017/S0305004100003236.
  61. ↑ Moore, C. B.; Eack, K. B.; Aulich, G. D.; Rison, W. (2001). "Energetic radiation associated with lightning stepped-leaders". Geophysical Research Letters 28 (11): 2141. Bibcode:2001GeoRL..28.2141M. doi:10.1029/2001GL013140.
  62. ↑ Dwyer, J. R.; Uman, M. A.; Rassoul, H. K.; Al-Dayeh, M.; Caraway, L.; Jerauld, J.; Rakov, V. A.; Jordan, D. M.; Rambo, K. J.; Corbin, V.; Wright, B. (2003). "Energetic Radiation Produced During Rocket-Triggered Lightning" (PDF). Science 299 (5607): 694–697. doi:10.1126/science.1078940. PMID 12560549.
  63. ↑ Newitz, A. (September 2007) "Educated Destruction 101", Popular Science, p. 61.
  64. ↑ Scientists close in on source of X-rays in lightning, Physorg.com, July 15, 2008. Retrieved July 2008.
  65. ↑ Prostak, Sergio (April 11, 2013). "Scientists Explain Invisible ‘Dark Lightning'". Sci-News.com. Retrieved July 9, 2013.
  66. ↑ Signature Of Antimatter Detected In Lightning – Science News. Sciencenews.org (December 5, 2009). Retrieved on June 23, 2012.
  67. ↑ Pliny the Younger. "Pliny the Younger's Observations". Archived from the original on June 25, 2003. Retrieved July 5, 2007. Behind us were frightening dark clouds, rent by lightning twisted and hurled, opening to reveal huge figures of flame.
  68. ↑ Dell'Amore, Christine (February 3, 2010) New Lightning Type Found Over Volcano?. National Geographic News.
  69. ↑ Strangeway, Robert J. (1995). "Plasma Wave Evidence for Lightning on Venus". Journal of Atmospheric and Terrestrial Physics 57 (5): 537–556. Bibcode:1995JATP...57..537S. doi:10.1016/0021-9169(94)00080-8. Retrieved September 24, 2007.
  70. ↑ Uman (1986) Ch. 4, pp. 26–34.
  71. ↑ Colvin, J. D.; Mitchell, C. K.; Greig, J. R.; Murphy, D. P.; Pechacek, R. E.; Raleigh, M. (1987). "An empirical study of the nuclear explosion-induced lightning seen on IVY-MIKE". Journal of Geophysical Research 92 (D5): 5696–5712. Bibcode:1987JGR....92.5696C. doi:10.1029/JD092iD05p05696.
  72. ↑ Uman (1986) pp. 103–110
  73. ↑ Fink, Micah. "How Lightning Forms". PBS.org. Public Broadcasting System. Retrieved September 21, 2007.
  74. ↑ National Weather Service (2007). "Lightning Safety". National Weather Service. Retrieved September 21, 2007.
  75. ↑ Uman (1986) p. 61.
  76. ↑ Rakov and Uman, p. 84.
  77. ↑ Thomson, E. M.; Uman, M. A.; Beasley, W. H. (January 1985). "Speed and current for lightning stepped leaders near ground as determined from electric field records". Journal of Geophysical Research 90 (D5): 8136. Bibcode:1985JGR....90.8136T. doi:10.1029/JD090iD05p08136.
  78. ↑ The Franklin Institute. Ben Franklin's Lightning Bells. Retrieved December 14, 2008.
  79. ↑ Rimstar.org Video demonstration of how Franklin's Bell worked
  80. ↑ "Lightning Detection Systems". Retrieved July 27, 2007. NOAA page on how the U.S. national lightning detection system operates
  81. ↑ "Vaisala Thunderstorm Online Application Portal". Archived from the original on September 28, 2007. Retrieved July 27, 2007. Real-time map of lightning discharges in U.S.
  82. ↑ Volland, H. (ed) (1995) Handbook of Atmospheric Electrodynamics, CRC Press, Boca Raton, ISBN 0849386470.
  83. ↑ "NASA Dataset Information". NASA. 2007. Retrieved September 11, 2007.
  84. ↑ "NASA LIS Images". NASA. 2007. Retrieved September 11, 2007.
  85. ↑ "NASA OTD Images". NASA. 2007. Retrieved September 11, 2007.
  86. ↑ Kridler, Chris (July 25, 2002). "Triggered lightning video" (video). requires QuickTime. Chris Kridler's Sky Diary. Retrieved September 24, 2007.
  87. ↑ Koopman, David W. & Wilkerson, T. D. (1971). "Channeling of an Ionizing Electrical Streamer by a Laser Beam". Journal of Applied Physics 42 (5): 1883–1886. Bibcode:1971JAP....42.1883K. doi:10.1063/1.1660462.
  88. ↑ Saum, K. A. & Koopman, David W. (November 1972). "Discharges Guided by Laser-Induced Rarefaction Channels". Physics of Fluids 15 (11): 2077–2079. Bibcode:1972PhFl...15.2077S. doi:10.1063/1.1693833.
  89. ↑ Schubert, C. W. (1977). "The laser lightning rod: A feasibility study". Technical report AFFDL-TR-78-60, ADA063847, [U.S.] Air Force Flight Dynamics Laboratory, Wright-Patterson AFB [Air Force Base] Ohio.
  90. ↑ Schubert, Charles W. & Lippert, Jack R. (1979). "Investigation into triggering lightning with a pulsed laser" (PDF). In Guenther, A. H. & Kristiansen, M. Proceedings of the 2nd IEEE International Pulse Power Conference, Lubbock, Texas, 1979. Piscataway, NJ: IEEE. pp. 132–135.
  91. ↑ Lippert, J. R. (1977). "A laser-induced lightning concept experiment". Final Report (Air Force Flight Dynamics Lab., Wright-Patterson AFB). Bibcode:1978affd.rept.....L.
  92. ↑ Rakov and Uman, pp. 296–299.
  93. ↑ "UNM researchers use lasers to guide lightning". Campus News, The University of New Mexico. January 29, 2001. Archived from the original on 2012-07-09. Retrieved July 28, 2007.
  94. ↑ Khan, N.; Mariun, N.; Aris, I.; Yeak, J. (2002). "Laser-triggered lightning discharge". New Journal of Physics 4: 61. doi:10.1088/1367-2630/4/1/361.
  95. ↑ Rambo, P.; Biegert, J.; Kubecek, V.; Schwarz, J.; Bernstein, A.; Diels, J.-C.; Bernstein, R. & Stahlkopf, K. (1999). "Laboratory tests of laser-induced lightning discharge". Journal of Optical Technology 66 (3): 194–198. doi:10.1364/JOT.66.000194.
  96. ↑ Ackermann, R.; Stelmaszczyk, K.; Rohwetter, P.; MéJean, G.; Salmon, E.; Yu, J.; Kasparian, J.; MéChain, G.; Bergmann, V.; Schaper, S.; Weise, B.; Kumm, T.; Rethmeier, K.; Kalkner, W.; WöSte, L.; Wolf, J. P. (2004). "Triggering and guiding of megavolt discharges by laser-induced filaments under rain conditions". Applied Physics Letters 85 (23): 5781. doi:10.1063/1.1829165.
  97. ↑ Wang, D.; Ushio, T.; Kawasaki, Z. -I.; Matsuura, K.; Shimada, Y.; Uchida, S.; Yamanaka, C.; Izawa, Y.; Sonoi, Y.; Simokura, N. (1995). "A possible way to trigger lightning using a laser". Journal of Atmospheric and Terrestrial Physics 57 (5): 459. doi:10.1016/0021-9169(94)00073-W.
  98. ↑ "Terawatt Laser Beam Shot in the Clouds Provokes Lightning Strike". News report based on: Kasparian, J.; Ackermann, R.; André, Y. B.; Méchain, G. G.; Méjean, G.; Prade, B.; Rohwetter, P.; Salmon, E.; Stelmaszczyk, K.; Yu, J.; Mysyrowicz, A.; Sauerbrey, R.; Woeste, L.; Wolf, J. P. (2008). "Electric events synchronized with laser filaments in thunderclouds". Optics Express 16 (8): 5757–63. doi:10.1364/OE.16.005757. PMID 18542684.
  99. ↑ "Laser Triggers Electrical Activity in Thunderstorm for the First Time". Newswise. Retrieved August 6, 2008. News report based on Kasparian et al. Méjean, pp. 5757–5763
  100. ↑ Graham, K.W.T. (1961). "The Re-magnetization of a Surface Outcrop by Lightning Currents". Geophysical Journal International 6: 85. Bibcode:1961GeoJI...6...85G. doi:10.1111/j.1365-246X.1961.tb02963.x.
  101. ↑ Cox A. (1961). Anomalous Remanent Magnetization of Basalt. U.S. Geological Survey Bulletin 1038-E, pp. 131–160.
  102. ↑ Bevan B. (1995). "Magnetic Surveys and Lightning". Near Surface Views (newsletter of the Near Surface Geophysics section of the Society of Exploration Geophysics). October 1995, pp. 7–8.
  103. ↑ Wasilewski, Peter; Günther Kletetschka (1999). "Lodestone: Nature's only permanent magnet – What it is and how it gets charged" (PDF). Geophysical Research Letters 26 (15): 2275–78. Bibcode:1999GeoRL..26.2275W. doi:10.1029/1999GL900496. Archived from the original (PDF) on October 3, 2006. Retrieved July 13, 2009.
  104. ↑ Sakai, H. S.; Sunada, S.; Sakurano, H. (1998). "Study of Lightning Current by Remanent Magnetization". Electrical Engineering in Japan 123 (4): 41–47. doi:10.1002/(SICI)1520-6416(199806)123:4<41::AID-EEJ6>3.0.CO;2-O.
  105. ↑ Archaeo-Physics, LLC | Lightning-induced magnetic anomalies on archaeological sites. Archaeophysics.com. Retrieved on June 23, 2012.
  106. ↑ Maki, David (2005). "Lightning strikes and prehistoric ovens: Determining the source of magnetic anomalies using techniques of environmental magnetism". Geoarchaeology: an International Journal 20 (5): 449–459. doi:10.1002/gea.20059.
  107. ↑ Verrier, V.; Rochette, P. (2002). "Estimating Peak Currents at Ground Lightning Impacts Using Remanent Magnetization". Geophysical Research Letters 29 (18): 1867. Bibcode:2002GeoRL..29r..14V. doi:10.1029/2002GL015207.
  108. ↑ "High-speed solar winds increase lightning strikes on Earth". Iop.org. 2014-05-15. Retrieved 2014-05-19.
  109. ↑ "IEEE Xplore". ieee.org. Retrieved October 15, 2015.
  110. ↑ Uman (1986) Ch. 6, p. 47.
  111. ↑ "Jesus actor struck by lightning". BBC News. October 23, 2003. Retrieved August 19, 2007.
  112. ↑ Picture of John Kaspar of the National States Rights Party speaking in front of the party’s lightning bolt flag (the flag was red, white, and blue). Mauryk2.com (November 6, 2010). Retrieved on April 9, 2013.
  113. ↑ "Lightning". Phar Lap: Australia's wonder horse. Museum Victoria.
  114. ↑ Hillier, Bevis (1968). Art Deco of the 20s and 30s. Studio Vista.

Bibliography

Further reading

External links

Wikiquote has quotations related to: Lightning
Wikimedia Commons has media related to Lightning.
Look up lightning in Wiktionary, the free dictionary.
This article is issued from Wikipedia - version of the Tuesday, May 03, 2016. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.