lightning

• 電撃性の、(事故の)雷撃

関

electric shock、electroconvulsive

　 　 　

WordNet

1. abrupt electric discharge from cloud to cloud or from cloud to earth accompanied by the emission of light
2. the flash of light that accompanies an electric discharge in the atmosphere (or something resembling such a flash); can scintillate for a second or more
3. a form of lightning that moves rapidly in a zigzag path with one end divided (fork-like) (同)chain lightning

PrepTutorEJDIC

1. 『いなずま』,雷光 / いなずまのような,す早い
2. 無警告ストライキ
3. =lightning rod
4. =firefly

Wikipedia preview

出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2013/01/29 12:35:32」(JST)

wiki ja

[Wiki ja表示]

Lightning

開発元	Mozilla Foundation
最新版	1.9 - 2012年11月14日 （2012-11-14）[+/-]
最新評価版	2.0b1  (2012年11月29日 （2012-11-29）)[+/-]
対応OS	Windows / Mac OS X / Linux
プラットフォーム	クロスプラットフォーム
種別	拡張機能
ライセンス	MPL/GPL/LGPL トリプルライセンス
公式サイト	Lightning :: Add-ons for Thunderbird

Lightning（らいとにんぐ）は Mozilla Foundation がオープンソースで開発を進めているスケジュール管理ソフトである。Mozilla Thunderbird および SeaMonkey 用の拡張機能で Thunderbird との連携に重点が置かれている。Mozilla Calendar プロジェクトにおいて開発が進められている。2006年3月にバージョン 0.1 がリリースされ、2007年2月に 0.3.1 がリリースされた。以後は Mozilla Sunbird と並行して開発が進められたが、Sunbird が打ち切りとなり、開発リソースは Lightning への一本化が行われた。

特徴

Thunderbird と連携していることにより、電子メールで受け取った iMIP イベントを容易にカレンダーに追加することが可能である。

また、WCAP をサポートした機能強化版も存在する。

iCal 形式、CSV 形式のファイルのインポート、エクスポートが可能である。WebDAV、CalDAV に対応しており、ローカルだけでなくネットワーク上のカレンダーを読み書きすることもできる。

2006年10月リリースのバージョン 0.3 では Gecko のバージョンを 1.9a1 に変更し、オプションの画面やアドオンの管理機能など複数の点が新しくなっている。また、このバージョンより Intel Mac に対応した。

2007年3月リリースのバージョン 0.3.1 では2007年からのアメリカ合衆国での夏時間の変更に対応した。これに伴い Windows 版ではOSのタイムゾーン更新プログラムを導入する必要がある。

2007年6月リリースのバージョン 0.5 より、拡張機能を導入することで Google Calendar との同期が可能になった。

バージョンの変遷

Thunderbird および SeaMonkey のメジャーアップデートに合わせて Lightning もバージョンアップされる。

バージョン	リリース日	対応する Thunderbird のバージョン	対応する SeaMonkey のバージョン
0.1	2006年3月14日	1.5	-
0.3.1	2007年2月19日	1.5 - 2.0	-
0.5	2007年6月27日	1.5 - 2.0	-
0.7	2007年10月25日	1.5 - 2.0	-
0.8	2008年4月4日	2.0	-
0.9	2008年9月23日	2.0	-
1.0b1	2010年1月12日	3.0	-
1.0b2	2010年6月24日	3.1	-
1.0b4	2011年6月27日	5.0	2.1 - 2.2
1.0b5	2011年7月29日	5.0 - 6.0	2.1 - 2.3
1.0b7	2011年9月26日	7.0	2.4
1.0	2011年11月7日	8.0	2.5
1.1	2011年12月16日	9.0	2.6
1.1.1	2012年1月5日
1.2	2012年1月23日	10.0	2.7
1.2.1	2012年2月3日
1.2.3	2012年3月3日
1.3	2012年3月9日	11.0	2.8
1.4	2012年4月23日	12.0	2.9
1.5	2012年6月4日	13.0	2.10
1.5.1	2012年6月14日
1.5.2	2012年6月21日
1.6	2012年7月12日	14.0	2.11
1.7	2012年8月25日	15.0	2.12
1.8	2012年10月3日	16.0	2.13
1.9	2012年11月14日	17.0	2.14

関連項目

• Mozilla Foundation - 開発元団体
• Mozilla Japan - 日本国内でMozilla製品のサポートを行う団体
• もじら組
• Mozilla - SunBirdのベースとなったソフトウェア
• SeaMonkey - Mozillaの後継
• Mozilla Firefox - SunBirdと同じように独立したタイプのWebブラウザ
• Mozilla Thunderbird - Mozillaのメール機能を独立させたクライアント
• Mozilla Sunbird - Lightningと同一のバックエンドを採用したスケジュール管理ソフト
• Nvu - MozillaのHTMLエディタ機能を独立させたソフトウェア

参考文献

外部リンク

• Calendarプロジェクト(日本語) - 本家ページの翻訳版
• Calendar Project(英語) - 本家サイト
• CPSS - 非公式日本語ロケール版を配布

wiki en

[Wiki en表示]

For other uses, see Lightning (disambiguation).

Lightning strikes during a thunderstorm

Lightning is a massive electrostatic discharge caused by unbalanced electric charges in the atmosphere, and resulting in a strike, from a cloud to itself, a cloud to a cloud or a cloud to ground, and accompanied by the loud sound of thunder.

Sound of a thunderstorm

A typical cloud to ground lightning strike is over 5 km (3 mi) long. A typical thunderstorm has three or more strikes per minute at its peak. Lightning is usually produced by cumulonimbus clouds up to 15 km high (9 mi) high, based 5–6 km (3-4 mi) above the ground. Lightning is caused by the circulation of warm moisture-filled air through electric fields. Ice or water particles then accumulate charge as in a Van de Graaff generator. Lightning may occur during snow storms (thundersnow), volcanic eruptions, dust storms, forest fires or tornadoes. Hurricanes typically generate some lightning, mainly in the rainbands as much as 160 km (100 mi) from the center.

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 lightning are still a matter of scientific investigation. The science of lightning is called fulminology. The fear of lightning is called astraphobia.

4-second video of a lightning strike, Island in the Sky, Canyonlands National Park, Utah, United States.

Frequency and distribution

World map of frequency of lightning strikes, in flashes per square kilometer per year

Main article: Distribution of lightning

Lightning strikes 40–50 times a second worldwide, for a total of nearly 1.4 billion flashes per year.

Cloud-to-ground (CG) lightning accounts for 25% of lightning globally. The base of the negative region in a cloud is typically at the elevation where freezing occurs. The closer this region is to the ground, the more likely cloud-to-ground strikes are. In the tropics, where the freeze zone is higher, 10% of lightning is CG. At the latitude of Norway (60° lat.) where the freezing elevation is lower, 50% of lightning is CG.

Lightning is not distributed evenly around the planet. About 70% of lightning occurs on land in the tropics, where most thunderstorms occur. The north and south poles and the areas over the oceans have the fewest lightning strikes. The place where lightning occurs most often is near the small village of Kifuka in the mountains of eastern Democratic Republic of the Congo, where the elevation is around 975 metres (3,200 ft). On average this region receives 158 lightning strikes per 1 square kilometer (0.39 sq mi) a year. Other hotspots include Catatumbo lightning in Venezuela, Singapore, Teresina in northern Brazil and "Lightning Alley" in Central Florida.

Formation

Cloud particle collision hypothesis

View of lightning from an airplane flying above a system.

According to this cloud particle charging hypothesis, charges are separated when ice crystals rebound off graupel. Charge separation appears to require strong updrafts which carry water droplets upward, supercooling them to between -10 and -40 °C (14 and -40 °F). These water droplets collide with ice crystals to form a soft ice-water mixture called graupel. Collisions between ice crystals and graupel pellets usually result in positive charge being transferred to the ice crystals, and negative charge to the graupel.

Updrafts drive the less heavy ice crystals upwards, causing the cloud top to accumulate increasing positive charge. Gravity causes the heavier negatively charged graupel to fall toward the middle and lower portions of the cloud, building up an increasing negative charge. Charge separation and accumulation continue until the electrical potential becomes sufficient to initiate a lightning discharge, which occurs when the distribution of positive and negative charges forms a sufficiently strong/high electric field.

Polarization mechanism hypothesis

The mechanism by which charge separation happens is still the subject of research. A hypothesised mechanism is polarization, which has two components:

1. Falling droplets of ice and rain become electrically polarized as they fall through the earth's magnetic field;
2. Colliding/rebounding cloud particles become oppositely charged.

There are several hypotheses for the origin of charge separation.

Initiation

Even assuming an electric field has been established, the mechanism by which the lightning discharge begins is not well known. Electric field measurements in thunderclouds are typically not large enough to directly initiate a discharge. Many hypotheses have been proposed, ranging from including runaway breakdown to locally enhanced electric fields near elongated water droplets or ice crystals. Percolation theory, especially for the case of biased percolation, describe random connectivity phenomena, which produce an evolution of connected structures similar to that of lightning strikes.

Development of cloud-to-ground lightning

Illustration of a negative leader (blue) meeting a positive streamer (red) and the return stroke. Click to watch the animation.

Electric field within the cloud's shadow

As a thundercloud moves over the surface of the Earth, an electric charge equal to but opposite the charge of the base of the thundercloud is induced on the Earth's surface below the cloud in its shadow. 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 drops as the thundercloud passes. The referential value of the induced surface charge could be represented as a bell curve.

The oppositely charged surfaces, thundercloud base above and the Earth's surfaces below, in turn create an electric field in the air between the two. This electric field varies in relation to the strength of the surface charge on the base of the thundercloud.

During discharge, there is a near instantaneous, measured in milliseconds, neutralization of the surface as positive charges race inward towards the strike termination. This rapid change, referred to as step potential, is often responsible for more injury or deaths than the strike itself, as electricity follows the path of least resistance, which may be up one leg and down another versus the more resistant ground surface. Thundercloud again induces charge on the ground, however this occurs over a much longer period of time.

(Downward) leader formation

High speed photography showing different parts of a lightning Flash during the Discharge process as seen in Toulouse, France.

A channel of ionized air, starts from a negatively charged region of mixed water and ice in the thundercloud. Ionized channels, the conductors for lighting discharge, are referred to as leaders as they travel outward from the original charge concentration and are invisible to the naked eye. The positively and negatively charged leaders proceed in opposite directions, positive upwards within the cloud, the negative towards the earth. Both ionic channels, proceed in their respective directions, in a number of successive spurts, similar to two kids hopping randomly in opposite directions. Each leader first "pools" as ions concentrate, then it shoots out in a straight line, momentarily pooling again to concentrate charged ions, before shooting out in another direction. It may split into two different directions, called branches in a fashion similar to a tree, resulting in multiple leaders. This process results in something resembling stairs and is referred to as "stepped leader(s)" once visible during discharge. The ionic channels continue this process until they near the Earth's surface.

About 90% of ionic channel lengths between "pools" are approximately 45 m (148 ft) in length, with most in the order of 50 to 100 m (164 to 328 ft). This initial phase involves a relatively small electric current (tens or hundreds of amperes). The progression of stepped leaders takes a comparatively long time (hundreds of milliseconds) to approach the ground. Researchers at the University of Florida found that the final one-dimensional speeds of 10 bolts observed were between 1.0×10⁵ and 1.4×10⁶ m/s, with an average of 4.4×10⁵ m/s.

Upward streamers

A lightning flash terminates [& discharge occurs] on a tree while an un-attached streamer is visible on the earth surface projection to the left.

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.

As negatively charged leaders approach, increasing the localized electric field strength, grounded objects already experiencing corona discharge exceed a threshold and form upward streamers. Once any downward leader connects to any upward leader available, a process referred to as "attachment", a circuit 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.

Return stroke

Once a channel of ionized air is established between the cloud and ground this becomes a path of least resistance and allows for a much greater current to propagate from the Earth back up the leader into the cloud. This is the return stroke and it is the most luminous and noticeable part of the lightning discharge.

Discharge

When the electric field becomes strong enough, an electrical discharge (the bolt of lightning) occurs within clouds or between clouds and the ground. During the strike, successive portions of air become a conductive discharge channel as the electrons and positive ions of air molecules are pulled away from each other and forced to flow in opposite directions.

The electrical discharge (averaging 30 kA for negative or 300 kA for positive lightning, and travelling at around 1×10⁸ m/s) rapidly superheats the discharge channel, causing the air to expand rapidly and produce a shock wave heard as thunder. The rolling and gradually dissipating rumble of thunder is caused by the time delay of sound coming from different portions of a long stroke.

Re-strike

Lightning is a highly visible form of energy transfer.

High speed videos (examined frame-by-frame) show that most lightning strikes are made up of multiple individual strokes. A typical strike is made of 3 or 4 strokes, though there may be more.

Each re-strike is separated by a relatively large amount of time, typically 40 to 50 milliseconds. Re-strikes can cause a noticeable "strobe light" effect.

Each successive stroke is preceded by intermediate dart leader strokes akin to, but weaker than, the initial stepped leader. The stroke usually re-uses the discharge channel taken by the previous stroke.

The variations in successive discharges are the result of smaller regions of charge within the cloud being depleted by successive strokes.^{[citation needed]}

The sound of thunder from a lightning strike is prolonged by successive strokes.

Types

Cloud-to-ground lightning

Some lightning strikes exhibit particular characteristics; scientists and the general public have given names to these various types of lightning. The lightning that is most-commonly observed is streak lightning. This is nothing more than the return stroke, the visible part of the lightning stroke. The majority of strokes occur inside a cloud so we do not see most of the individual return strokes during a thunderstorm.^{[citation needed]}

Cloud-to-ground

Cloud-to-ground is the best known and second most common type of lightning. Of all the different types of lightning, it poses the greatest threat to life and property since it strikes the ground. Cloud-to-ground (CG) lightning is a lightning discharge between a cumulonimbus cloud and the ground. It is initiated by a leader stroke moving down from the cloud.

Bead lightning is a type of cloud-to-ground lightning which appears to break up into a string of short, bright sections, which last longer than the usual discharge channel. It is relatively rare. Several theories have been proposed to explain it; one is that the observer sees portions of the lightning channel end on, and that these portions appear especially bright. Another is that, in bead lightning, the width of the lightning channel varies; as the lightning channel cools and fades, the wider sections cool more slowly and remain visible longer, appearing as a string of beads.

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

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. These are often found in the visual vault area near the mesocyclone of rotating thunderstorms and coincides with intensification of thunderstorm updrafts. A 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.^{[citation needed]}

Forked lightning is a name, not in formal usage, for cloud-to-ground lightning that exhibits branching of its path.

Ground-to-cloud

Ground to cloud lightning is an artificially initiated, or triggered, category of ground flashes. Triggered lightning goes from tall structures on the ground, such as towers on mountains, to clouds.

Positive lightning

Local variations in cloud formations can cause the bottom of a cloud to accumulate a positive charge which will induce a negative charge on the ground. Lightning can occur with both positive and negative polarity. 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. An average bolt of positive lightning carries an electric current of about 300 kA — about 10 times that of negative lightning.

Anvil-to-ground (Bolt from the blue) lightning strike.

Unlike the far more common "negative" lightning, positive lightning occurs when a positive charge is carried by the top of the clouds (generally anvil clouds) rather than the ground. Generally, this causes the leader arc to form in the anvil of the cumulonimbus and travel horizontally for several miles before veering down to meet the negatively charged streamer rising from the ground. The 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 makes up less than 5% of all lightning strikes.

Because of the much greater distance they must travel before discharging, positive lightning strikes typically carry six to ten times the charge and voltage difference of a negative bolt and last around ten times longer. During a positive lightning strike, huge quantities of ELF and VLF radio waves are generated.

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. 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, however it is unclear whether adequate protection against positive lightning was incorporated.

Positive lightning is also now believed to have been responsible for the 1963 in-flight explosion and subsequent crash of Pan Am Flight 214, a Boeing 707. Due to the dangers of lightning, aircraft operating in U.S. airspace have been required to have static discharge wicks to reduce the possibility of attracting a lightning strike, as well as to mitigate radio interference due to static buildup through friction with the air, but these measures may be insufficient for positive lightning.

Positive lightning has also been shown to trigger the occurrence of upper atmosphere lightning. It tends to occur more frequently in winter storms, as with thundersnow, and at the end of a thunderstorm.

Dry lightning

Main article: Dry lightning

Dry lightning is a term in Australia, Canada and the United States for lightning that occurs with no precipitation at the surface. This type of lightning is the most common natural cause of wildfires. Pyrocumulus clouds produce lightning for the same reason that it is produced by cumulonimbus clouds.

Rocket lightning

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.

Cloud-to-cloud

Multiple paths of cloud-to-cloud lightning, Swifts Creek, Australia.

Cloud-to-cloud lightning, Victoria, Australia.

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.

These are most common 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. The "heat" portion of the term is a folk association between locally experienced warmth and the distant lightning flashes.

Another terminology used for cloud–cloud or cloud–cloud–ground lightning is "Anvil Crawler", due to the habit of the charge typically originating from beneath or within the anvil and scrambling through the upper cloud layers of a thunderstorm, normally generating multiple branch strokes which are dramatic to witness. 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.

Sheet lightning is an informal name for cloud-to-cloud lightning that exhibits a diffuse brightening of the surface of a cloud, caused by the actual discharge path being hidden or too far away. The lightning itself cannot be seen by the spectator, so it appears as only a flash, or a sheet of light. The lightning may be too far away to discern individual flashes.

Heat lightning is a common name for a lightning flash that appears to produce no discernable thunder because it occurs too far away for the thunder to be heard. The sound waves dissipate before they reach the observer.

Triggered lightning

Rocket-triggered

Lightning has been triggered by launching lightning rockets carrying trailing spools of wire into thunderstorms. The wire unwinds as the rocket ascends, providing a path for lightning. These bolts are typically very straight due to the straight path created by the wire.

The International Center for Lightning Research and Testing (ICLRT) at Camp Blanding, Florida typically uses rocket induced lightning in their research studies.

Lightning has also been triggered directly by other human activities: Airplanes among other flying aircrafts can trigger lightning. Furthermore, lightning struck Apollo 12 soon after takeoff, and has struck soon after thermonuclear explosions.

Volcanically triggered

Volcanic material thrust high into the atmosphere can trigger lightning.

See also: Dirty thunderstorm

There are three types of volcanic lightning:

• Extremely large volcanic eruptions, which eject gases and material high into the atmosphere, can trigger lightning. This phenomenon was documented by Pliny The Younger during the 79 AD eruption of Vesuvius, in which his uncle perished.

• An intermediate type which comes from a volcano's vents, sometimes 2.9 km long.
• Small spark-type lightning about .91 meters long lasting a few milliseconds.

Laser-triggered

Since the 1970s, researchers have attempted to trigger lightning strikes by means of infrared or ultraviolet lasers, which create a channel of ionized gas through which the lightning would be conducted to ground. Such triggering of lightning is intended to protect rocket launching pads, electric power facilities, and other sensitive targets.

In New Mexico, U.S., scientists tested a new terawatt laser which provoked lightning. Scientists fired ultra-fast pulses from an extremely powerful laser thus sending several terawatts into the clouds to call down electrical discharges in storm clouds over the region. The laser beams sent from the laser make channels of ionized molecules known as "filaments". Before the lightning strikes earth, the filaments lead electricity through the clouds, playing the role of lightning rods. Researchers generated filaments that lived too short a period to trigger a real lightning strike. Nevertheless, a boost in electrical activity within the clouds was registered. According to the French and German scientists, who ran the experiment, the fast pulses sent from the laser will be able to provoke lightning strikes on demand. Statistical analysis showed that their laser pulses indeed enhanced the electrical activity in the thundercloud where it was aimed—in effect they generated small local discharges located at the position of the plasma channels.

Extraterrestrial lightning

Lightning has been observed within the atmospheres of other planets, such as Venus, Jupiter and Saturn. 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 '80s, signals suggesting lightning may be present in the upper atmosphere were detected. 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 to originate from lightning on Venus.

Physical effects

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. 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 five seconds would be about one mile (1.6 km) (5x340 m) distant. A flash preceding thunder by three seconds is about one kilometer (0.62 mi) (3x340 m) distant. 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, and 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 but no evidence was found until 2001/2002, when researchers at the New Mexico Institute of Mining and Technology detected X-ray emissions from an induced lightning strike along a 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. 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.

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 discovery of the clear signatures of antimatter produced in lightning.

Lightning-induced magnetism

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

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 but sometimes vertically, where faults, ore bodies, or ground water offers a less resistive path. One theory suggests that lodestones, natural magnets encountered in ancient times, were created in this manner.

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

Human factors

Detection

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. 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 arrive at several receivers can be used to locate the source of the discharge. The United States federal government has constructed a nation-wide grid of such lightning detectors, allowing lightning discharges to be tracked in real time throughout the continental U.S.

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.

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.

Harvesting lightning energy

Main article: Harvesting lightning energy

Since the late 1980s, there have been several attempts to investigate the possibility of harvesting energy from lightning. While a single bolt of lightning carries a relatively large amount of energy (approximately 5 billion joules), this energy is concentrated in a small location and is passed during an extremely short period of time (milliseconds); therefore, extremely high electrical power is involved. It has been proposed that the energy contained in lightning be used to generate hydrogen from water, or to harness the energy from rapid heating of water due to lightning.

A technology capable of harvesting lightning energy would need to be able to rapidly capture the high power involved in a lightning bolt. The ever-changing energy involved in each lightning bolt is a problem. Additionally, lightning is sporadic, and therefore energy would have to be collected and stored; it is difficult to convert high-voltage electrical power to the lower-voltage power that can be stored. Another major challenge when attempting to harvest energy from lightning is the impossibility of predicting when and where thunderstorms will occur. Even during a storm, it is very difficult to tell where exactly lightning will strike.

In culture

Further information: Lightning in religion

In many cultures, lightning has been viewed as part of a deity or a deity in of itself. These include the Greek god Zeus, the Aztec god Tlaloc, the Mayas' God K, Slavic mythology's Perun, the Baltic Pērkons/Perkūnas, Thor in Norse mythology, Ukko in Finnish mythology, the Hindu god Indra, the Shinto god Raijin, and the Mormon god Elohim. 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.

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). 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. The Schutzstaffel, the secret police 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.

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. 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.

Related phenomena

Ball lightning

Main article: Ball lightning

Ball lightning may be an atmospheric electrical phenomenon, the physical nature of which is still controversial. The term refers to reports of luminous, usually spherical objects which vary from pea-sized to several meters in diameter. It is sometimes associated with thunderstorms, but unlike lightning flashes, which last only a fraction of a second, ball lightning reportedly lasts many seconds. Ball lightning has been described by eyewitnesses but rarely recorded by meteorologists. Scientific data on natural ball lightning is scarce owing to its infrequency and unpredictability. The presumption of its existence is based on reported public sightings, and has therefore produced somewhat inconsistent findings.

Laboratory experiments have produced effects that are visually similar to reports of ball lightning, but at present, it is unknown whether these are actually related to any naturally occurring phenomenon. One theory is that ball lightning may be created when lightning strikes silicon in soil, a phenomenon which has been duplicated in laboratory testing. Given inconsistencies and the lack of reliable data and completely contradicting and unpredictable behavior, the true nature of ball lightning is still unknown and was often regarded as a fantasy or a hoax.

Reports of the phenomenon were dismissed for lack of physical evidence, and were often regarded the same way as UFO sightings. Severely contradicting descriptions of ball lightning makes it impossible even to create a plausible hypothesis that will take into account described behavior.

Natural ball lightning appears infrequently and unpredictably, and is therefore rarely (if ever truly) photographed. However, several purported photos and videos exist. Perhaps the most famous story of ball lightning unfolded when 18th-century physicist Georg Wilhelm Richmann installed a lightning rod in his home and was struck in the head – and killed – by a "pale blue ball of fire."

Upper-atmospheric discharges

Main article: Upper-atmospheric lightning

Representation of upper-atmospheric lightning and electrical-discharge phenomena

Sprites are large-scale electrical discharges that occur high above a thunderstorm cloud, giving rise to a range of visual shapes. They are triggered by the discharges of positive lightning between the thundercloud and the ground. The phenomena were named after the mischievous sprite (air spirit) Puck in Shakespeare's A Midsummer Night's Dream. They often occur in clusters, lying 50 to 90 kilometres (31 to 56 mi) above the Earth's surface. Sprites have been mentioned as a possible cause in otherwise unexplained accidents involving high altitude vehicular operations above thunderstorms.

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 25 miles (40 km) to 50 miles (80 km) above the earth. They are also brighter than sprites and, as implied by their name, are blue in colour.

ELVES often appear as dim, flattened, circular in the horizontal plane, expanding glows around 250 miles (400 km) in diameter that last for, typically, just one millisecond. They occur in the ionosphere 60 miles (97 km) above the ground over thunderstorms. Their color was a puzzle for some time, but is now believed to be a red hue. Elves is an acronym for Emissions of Light and Very Low Frequency Perturbations from Electromagnetic Pulse Sources. This refers to the process by which the light is generated; the excitation of nitrogen molecules due to electron collisions (the electrons possibly having been energized by the electromagnetic pulse caused by a discharge from the Ionosphere).

See also

• Atmospheric convection
• Dry thunderstorm
• Keraunomedicine: the medical study of lightning casualties
• Lichtenberg figure
• Lightning safety
• National Weather Service: NWS
• National Oceanic and Atmospheric Administration: NOAA
• Paleolightning
• Radio atmospheric
• St. Elmo's fire
• USAF 45th Weather Squadron: lightning safety for rocket launches
• Vela satellites: satellites which could record lightning superbolts
• Whistler (radio)

References

Notes

Bibliography

• Rakov, Vladimir A. and Uman, Martin A. (2003). Lightning: Physics and effects. Cambridge, England: Cambridge University Press. ISBN 0521583276. http://books.google.com/books?id=NviMsvVOHJ4C&pg=PA296.

• Uman, Martin A. (1986). All About Lightning. Dover Publications, Inc.. pp. 103–110. ISBN 978-0-486-25237-7.

Further reading

• My Very Close Encounters With Florida Lightning Bolts By Thomas F. Giella, retired Meteorologist and Solar and Space Plasma Physicist
• Alex Larsen (1905). "Photographing Lightning With a Moving Camera". Annual Report Smithsonian Institution 60 (1): 119–127.

• André Anders (2003). "Tracking Down the Origin of Arc Plasma Science I. Early Pulsed and Oscillating Discharges". IEEE Transactions on Plasma Science 31 (4): 1052–1059. Bibcode 2003ITPS...31.1052A. doi:10.1109/TPS.2003.815476. This is also available at "Energy Citations Database (ECD) – Sponsored by OSTI" (PDF). Osti.gov. http://www.osti.gov/energycitations/servlets/purl/823201-oEL59M/native/823201.pdf. Retrieved September 5, 2008.

• Anna Gosline (May 2005). "Thunderbolts from space". New Scientist 186 (2498): 30–34. http://www.newscientist.com/article/mg18624981.200.

Sample, in .pdf form, consisting of all of the book through page 20.

• The Mirror of Literature, Amusement, and Instruction, Vol. 12, Issue 323, July 19, 1828 The Project Gutenberg eBook (early lightning research)

External links

• How Lightning Works at HowStuffWorks
• How to survive in a lightning storm A guide for children and youth
• Lightning Safety Page – National Weather Service Pueblo Colorado
• Outdoor guide to lightning safety and first-aid
• Map of lightning strikes in USA over last 60 minutes
• Live storm data and sferics for southern England Generated by data recorded by a weather station at Newport, Isle of Wight, UK
• Thunderstorms and Lightning at the Open Directory Project
• Colorado Lightning Resource Center
• Webarchive: April 25, 1997 Sandia-led research may zap old beliefs about lightning protection at critical facilities; Triggered lightning tests leading to safer storage bunkers
• 2003-11-06, ScienceDaily: Thunderstorm Research Shocks Conventional Theories; Florida Tech Physicist Throws Open Debate On Lightning's Cause
• European Cooperation for Lightning Detection
• NASA Finds Lightning Clears Safe Zone in Earth's Radiation Belt
• National Geographic Lightning Simulator
• Lightning strikes governed by moving cloud layers – the first theory to fully explain lightning formation and dynamics, New Scientist, March 23, 2008
• Signature of Antimatter Detected in Lightning
• WWLLN World Wide Lightning Location Network

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「electroconvulsive」

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