#Edit this page Wikipedia (en) copyright Wikipedia Atom feed Lightning From Wikipedia, the free encyclopedia Jump to: navigation, search For other uses, see Lightning (disambiguation). This article has multiple issues. Please help improve it or discuss these issues on the talk page. This article needs attention from an expert in meteorology. The specific problem is: incorrect type classification. See the talk page for details. WikiProject Meteorology may be able to help recruit an expert. (September 2012) Exclamation mark with arrows pointing at each other This article appears to contradict itself. Please see the talk page for more information. (August 2012) This article's factual accuracy is disputed. Please help to ensure that disputed statements are reliably sourced. See the relevant discussion on the talk page. (August 2012) 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. A typical cloud to ground lightning strike jumps a 5 km (3 mi) gap through the air.^[1] A typical thunderstorm has three or more strikes per minute at its peak.^[2] Lightning is usually produced by cumulonimbus clouds based 5-6 km (3-4 mi) above the ground and that are themselves up to 15 km (9 mi) in height. Lightning also occurs during snow storms (thundersnow), volcanic eruptions, dust storms, forest fires or tornadoes.^[3]^[4] Hurricanes typically generate some lightning, mainly in the rainbands as much as 160 km (100 mi) from the center.^[5]^[6]^[7] 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.^[8]^[9] Lightning may be caused by the circulation of warm moisture-filled air through electric fields.^[10] Ice or water particles then accumulate charge as in a Van de Graaff generator.^[11] The science of lightning is called fulminology.^[12] The fear of lightning is called astraphobia. Sorry, your browser either has JavaScript disabled or does not have any supported player. You can download the clip or download a player to play the clip in your browser. Sound of a thunderstorm Sorry, your browser either has JavaScript disabled or does not have any supported player. You can download the clip or download a player to play the clip in your browser. 4-second video of a lightning strike, Island in the Sky, Canyonlands National Park, Utah, United States. Contents * 1 General properties * 2 Charge separation & cloud polarization + 2.1 Cloud particle collision hypothesis + 2.2 Polarization mechanism hypothesis + 2.3 Flash initiation * 3 Development of cloud-to-ground lightning + 3.1 Electric field within the cloud's shadow + 3.2 (Downward) leader formation + 3.3 Upward streamers + 3.4 Attachment + 3.5 Discharge + 3.6 Properties of CG lightning flashes * 4 Types + 4.1 Cloud to ground (CG) + 4.2 Cloud to cloud (CC) + 4.3 Intracloud (IC) + 4.4 Lightning events * 5 Effects + 5.1 Lightning srike + 5.2 Thunder + 5.3 High energy radiation + 5.4 Lightning-induced magnetism * 6 Triggered lightning + 6.1 Rocket-triggered + 6.2 Volcanically triggered + 6.3 Laser-triggered * 7 Extraterrestrial lightning * 8 Human factors + 8.1 Detection + 8.2 Harvesting lightning energy + 8.3 In culture * 9 Related phenomena + 9.1 Upper-atmospheric discharges * 10 See also * 11 References + 11.1 Notes + 11.2 Bibliography * 12 Further reading * 13 External links [edit] General properties Lightning frequency measured in flashes per square kilometer per year Main article: Distribution of lightning Lightning occurs approximately 40-50 times a second worldwide, resulting in nearly 1.4 billion flashes per year.^[13] Many factors affect the frequency, distribution, strength, and physical properties of a typical lightning flash. 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 in-cloud (IC), cloud-to-cloud (CC), and cloud-to-ground (CG) lightning varies. In general, cloud-to-ground lightning flashes are around 25% of all total lightning flashes worldwide. The base of the negative region in a cloud is typically at the elevation where the freezing level occurs; so, the closer this region is to the ground, the more likely CG strikes are. In the tropics, where the freezing level is generally higher, 10% of lightning is CG. At the latitude of Norway (around 60° North latitude), where the freezing elevation is lower, 50% of lightning is CG.^[14]^[15] Lightning is not distributed evenly around the planet.^[16] 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 on planet Earth is near the small village of Kifuka in the mountains of the eastern Democratic Republic of the Congo,^[17] 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) per year.^[18] Other lightning hotspots include Catatumbo lightning in Venezuela, Singapore,^[19] Teresina in northern Brazil^[20], and "Lightning Alley" in Central Florida.^[21]^[22] [edit] Charge separation & cloud polarization [edit] 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.^[23] 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.^[23] [edit] 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:^[24] 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.^[25]^[26]^[27] [edit] Flash initiation Even assuming an electric field has been established, the mechanism by which the lightning flash begins is not well known. Electric field measurements in thunderclouds are typically not large enough to directly initiate the resulting discharge.^[28] Many hypotheses have been proposed, ranging from including runaway breakdown to locally enhanced electric fields near elongated water droplets or ice crystals.^[29] Percolation theory, especially for the case of biased percolation,^[30] describe random connectivity phenomena, which produce an evolution of connected structures similar to that of lightning strikes. [edit] 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. 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 repeatably 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. [edit] 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. [edit] (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.^[31] 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.^[32] 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 "alternating" currents during discharge. [edit] 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.^[33]^[34] As negatively charged leaders approach, increasing the localized electric field strength, grounded objects already experiencing corona discharge exceed a threshold and form upward streamers. [edit] Attachment Once any downward leader connects to any upward leader available, a process referred to as "attachment", a low resistance 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.^[35] [edit] Discharge Return stroke Once the ionic channel is established, bridging the highly resistant air between the negative charges in the cloud and the positive surface charges on the Earth the thundercloud induced, the flood gates are opened allowing for electrical discharge to occur. Neutralization of surface charges occurs first, with an enormous current of positive charges racing up the ionic channel towards the thundercloud. This is the 'return stroke' and it is the most luminous and noticeable part of the lightning discharge. The electrical current of the return stroke averages 30 kiloAmps for a typical CG flash, often referred to as "negative" lightning. A much less likely lightning flash originating from the ground, usually from very tall structures, known as "positive" lightning, can achieve 300 kAmps during the return stroke. The rate at which the return stroke current travels has been found to be around 1×10^8 m/s^[36]) The massive transfer of current during the return stroke, and the rate at which is occurs measured in microseconds, rapidly superheats the ionic channel forming plasma and collapses once the current either reverses or stops. This near instantaneous current transfer causes the air to expand rapidly and produce a shock wave heard as thunder. Re-strike Lightning is a highly visible form of energy transfer. High speed videos (examined frame-by-frame) show that most lightning flashes are made up of multiple individual strokes. A typical CG flash is made of 3 or 4 strokes, though there may be more.^[37] 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.^[38] 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.^[39] Alternating current of the flash Because discharge of both the ground surface charges and the localized cloud charge in the region of stepped leader origin occurs in an alternating fashion until charge equalization is reached, the current is said to be more alternating (AC) in nature than as a single direction current (DC). Each successive stroke is significantly lower in strength than the stroke that proceeded it due to the depletion of the polarized charges concentrated at each end of the flash channel. This alternating current nature of a lightning flash results in several phenomena needing to be addressed in the protection of ground-based structures. Alternating currents travel on the surface of any conductor, known as skin_effect, unlike direct currents "flowing through" a conductor like water in a hose. Hence, conductors used in the protection of facilities tend to be multi-stranded small wires weaved together, that increases the surface area inversely in proportion to cross-sectional area which is more important to direct currents. Alternating currents also are impacted by a different form of "resistance" known as impedance and needs to be addressed in a different fashion than direct current's electrical resistance. The lightning flash's AC properties also result in the propagation of electromagnetic pulses (EMPs) outward from the ionic channel. These degrade rapidly as their distance from the origin increases, however if they pass over conductive elements; i.e., 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 series with these conductors 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. [edit] Properties of CG lightning flashes The rolling and gradually dissipating rumble of thunder is caused by the time delay of sound coming from different portions of a long stroke.^[40] Researchers at the University of Florida found that the final one-dimensional speeds of 10 flashes observed were between 1.0×10^5 and 1.4×10^6 m/s, with an average of 4.4×10^5 m/s.^[41] [edit] Types Cloud-to-ground lightning 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, that primarily originates in the thundercloud and terminates on an Earth surface, but may also occur in the reverse direction aka 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. Also there are different anthropocentric observations and common names used to describe a particular lightning event, which may confuse the understanding of lightning by the layman or general public, but can be attributed to the same or different events. [edit] 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 primarily initiated by a downward stepped leader moving down from the cloud. * Ground-to-cloud lightning is an artificially initiated, or triggered, category of CG flashes. Triggered lightning goes from tall structures on the ground, such as towers on mountains, to clouds.^[42] * 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.^[43] An average bolt of positive lightning carries an electric current of about 300 kA -- about 10 times that of negative lightning.^[44] 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.^[45] 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.^[46] During a positive lightning strike, huge quantities of ELF and VLF radio waves are generated.^[47] 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.^[48] 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,^[49] however it is unclear whether adequate protection against positive lightning was incorporated.^[50]^[51] 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.^[52] 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.^[53] 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.^[23] [edit] Cloud to cloud (CC) 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.^[23] 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. [edit] Intracloud (IC) [edit] Lightning events * 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.^[54] 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.^[55] 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.^[56] Given inconsistencies and the lack of reliable data and completely contradicting and unpredictable behavior, the true nature of ball lightning is still unknown^[57] and was often regarded as a fantasy or a hoax.^[58] Reports of the phenomenon were dismissed for lack of physical evidence, and were often regarded the same way as UFO sightings.^[57] 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."^[59] Main article: Ball lightning * 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.^[60]^[61] * 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.^[62] Pyrocumulus clouds produce lightning for the same reason that it is produced by cumulonimbus clouds. Main article: Dry lightning * Forked lightning is a name, not in formal usage, for cloud-to-ground lightning that exhibits branching of its path. * 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.^[63] * 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] * 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.^[64] * 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. * 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.^[65] 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] [edit] Effects [edit] Lightning srike Main article: Lightning strike Objects struck by lightning experience heat and magnetic forces of great magnitude. Lighting current travelling through a tree may heat its sap to boiling and burst it. Sand or soil struck by lightning may melt and form fulgarites. Humans or animals struck by lighting may be killed of suffer sever injury due to electrical burns. Buildings or tall structures hit by lighting may be damaged; a lightning rod system can greatly reduce the probability of severe property damage. [edit] 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 (O[3]). [edit] High energy radiation The production of X-rays by a bolt of lightning was theoretically predicted as early as 1925^[66] but no evidence was found until 2001/2002,^[67] 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.^[68] 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.^[69] [edit] 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^[70]^[71] but sometimes vertically, where faults, ore bodies, or ground water offers a less resistive path.^[72] One theory suggests that lodestones, natural magnets encountered in ancient times, were created in this manner.^[73] Lightning-induced magnetic anomalies can be mapped in the ground,^[74]^[75] and analysis of magnetized materials can confirm lightning was the source of the magnetization^[76] and provide an estimate of the peak current of the lightning discharge.^[77] [edit] Triggered lightning [edit] 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.^[78] 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.^[79] Furthermore, lightning struck Apollo 12 soon after takeoff, and has struck soon after thermonuclear explosions.^[80] [edit] 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.^[81] * 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.^[82] [edit] Laser-triggered Since the 1970s,^[83]^[84]^[85]^[86]^[87]^[88] 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.^[89]^[90]^[91]^[92]^[93] 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.^[94] 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.^[95] [edit] 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.^[96] 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.^[97] [edit] Human factors [edit] 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.^[98] 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.^[99]^[100] 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.^[101] 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.^[102]^[103]^[104] [edit] 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^[105]), 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.^[106] 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,^[107] or to use inductors spaced far enough away so that a safe fraction of the energy might be captured.^[108] 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.^[107] 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.^[105] [edit] 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 Perkons/Perkunas, Thor in Norse mythology, Ukko in Finnish mythology, the Hindu god Indra, the Shinto god Raijin, and the Mormon god Elohim.^[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. 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 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.^[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. [edit] Related phenomena [edit] 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.^[47] 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.^[115] 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.^[116] 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.^[117] 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.^[118] 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).^[119] [edit] See also Portal icon Environment portal * 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) [edit] References Constructs such as ibid., loc. cit. and idem are discouraged by Wikipedia's style guide for footnotes, as they are easily broken. Please improve this article by replacing them with named references (quick guide), or an abbreviated title. (September 2012) [edit] Notes 1. ^ Uman, Martin A.' "All About Lightning"; p. 81; Dover Publications N.Y.; 1986; ISBN- 2-486-25237-x 2. ^ Uman, Martin A.' "All About Lightning"; p. 55; Dover Publications N.Y.; 1986; ISBN- 2-486-25237-x 3. ^ New Lightning Type Found Over Volcano?. News.nationalgeographic.com (February 2010). Retrieved on June 23, 2012. 4. ^ "Bench collapse sparks lightning, roiling clouds". Vulcano Watch. United States Geological Society. June 11, 1998. http://hvo.wr.usgs.gov/volcanowatch/1998/98_06_11.html. Retrieved October 7, 2012. 5. ^ Hurricane lightning [1] Accesssed 27 Jul 2012 6. ^ Hurricane Lightning [2] Accessed 17 Jul 2012 7. ^ Long Range Lightning Detection Network [3] Accessed 27 Jul 2012 8. ^ Micah Fink for PBS. "How Lightning Forms". Public Broadcasting System. http://www.pbs.org/wnet/savageplanet/03deadlyskies/01lforms/indexm id.html. 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Retrieved March 5, 2013. 109. ^ Widstoe, John A. A Rational Theology Salt Lake City:1915 Bookcraft 110. ^ Uman (1986), Ch. 6, p. 47 111. ^ "Jesus actor struck by lightning". BBC News International Version. October 23, 2003. http://news.bbc.co.uk/2/hi/entertainment/3209223.stm. 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): 113. ^ "Lightning". Phar Lap: Australia's wonder horse. Museum Victoria. http://museumvictoria.com.au/pharlap/horse/lightning.asp. 114. ^ Hillier, Bevis Art Deco 1971 115. ^ STRATOCAT - Stratospheric balloons history and present. "Full report on the uncontrolled free fall of a stratospheric balloon payload provoked by a Sprite". http://stratocat.com.ar/fichas-e/1989/PAL-19890605.htm. 116. ^ UNIVERSE: Cosmic Phenomena(2009), History Channel, aired 9-10am MDT 117. ^ W. Wayt Gibbs. "Lightning's strange cousins flicker faster than light itself". Scientific American. http://www-star.stanford.edu/~vlf/optical/press/elves97sciam/. Retrieved September 24, 2007. 118. ^ Boeck, William L.; Vaughan, Otha H.; Blakeslee, R.J.; Vonnegut, Bernard; Brook, Marx (1998). "The role of the space shuttle videotapes in the discovery of sprites, jets and elves". Journal of Atmospheric and Solar-Terrestrial Physics 60 (7-9): 669. Bibcode 1998JASTP..60..669B. doi:10.1016/S1364-6826(98)00025-X. 119. ^ Holoscience.com. "Image of lightning types and altitudes" (.jpg). Holoscience.com. http://www.holoscience.com/news/img/Sprites.jpg. Retrieved September 24, 2007. [edit] 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. [edit] Further reading * My Very Close Encounters With Florida Lightning Bolts^[dead link] 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/na tive/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) [edit] External links Wikimedia Commons has media related to: Lightning Look up lightning in Wiktionary, the free dictionary. * 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 * v * t * e Meteorological data and variables General * Adiabatic processes * Lapse rate * Lightning * Surface solar radiation * Surface weather analysis * Visibility * Vorticity * Wind Condensation * Cloud * Cloud condensation nuclei * Fog * Lifted condensation level (LCL) * Precipitation * Water vapor Convection * Convective available potential energy (CAPE) * Convective inhibition (CIN) * Convective instability * Convective temperature (T[c]) * Equilibrium level (EL) * Helicity * Level of free convection (LFC) * Lifted index (LI) * Bulk Richardson number (BRN) Temperature * Dew point (T[d]) * Equivalent temperature (T[e]) * Forest fire weather index * Haines Index * Heat index * Humidex * Humidity * Potential temperature (th) * Equivalent potential temperature (th[e]) * Sea surface temperature (SST) * Wet-bulb temperature * Wet-bulb potential temperature * Wind chill Pressure * Atmospheric pressure * Baroclinity * Barotropicity * v * t * e Atmospheric electricity General * Geophysics * Atmospheric sciences * Atmospheric physics * Atmospheric dynamics * Atmospheric dynamo * Atmospheric chemistry * Earth's magnetic field Electromagnetism ELF/VLF Electromagnetic emissions * Radio atmospherics * Whistlers * Chorus * Hiss Optical emissions * Transient luminous events * Upper-atmospheric lightning * Sprites * St. Elmo's fire * Ball lightning Sources * Solar radiation * Lightning * Equatorial electrojet Applications * Electrodynamic tethers * Magnetotellurics People * Georg Wilhelm Richmann * Egon Schweidler * Nikola Tesla Retrieved from "http://en.wikipedia.org/w/index.php?title=Lightning&oldid=544459120" Categories: * Lightning * Electrical phenomena * Space plasmas * Weather hazards * Storm Hidden categories: * Use mdy dates from October 2012 * Meteorology articles needing expert attention * Articles needing expert attention from September 2012 * All articles needing expert attention * Self-contradictory articles from August 2012 * All self-contradictory articles * Accuracy disputes from August 2012 * All accuracy disputes * All articles with unsourced statements * Articles with unsourced statements from October 2011 * Articles with ibid from September 2012 * All articles with dead external links * Articles with dead external links from June 2011 Navigation menu Personal tools * Create account * Log in Namespaces * Article * Talk Variants Views * Read * Edit * View history Actions Search ____________________ (Submit) Search Navigation * Main page * Contents * Featured content * Current events * Random article * Donate to Wikipedia Interaction * Help * About Wikipedia * Community portal * Recent changes * Contact Wikipedia Toolbox * What links here * Related changes * Upload file * Special pages * Permanent link * Page information * Cite this page Print/export * Create a book * Download as PDF * Printable version Languages * Afrikaans * emarNa * a+l+e+r+b+y+tm * ª¡ * Aymar aru * Belaruskaya * Belaruskaya (tarashkeviica) * B"lgarski * Bosanski * Català * CHvashla * Cesky * ChiShona * Corsu * Cymraeg * Dansk * Deutsch * Ellynika' * Español * Esperanto * Estremeñu * Euskara * f+a+r+s+ * Français * Frysk * Gaeilge * Gaelg * Galego * * ­´ * ¡µ¥¥¶ * ¹¿¨¦ * Hrvatski * Ido * Bahasa Indonesia * ¦/inuktitut * Íslenska * Italiano * E+B+R+J+T+ * Basa Jawa * ¨¨¡ * ¥ £ * Kiswahili * Kurdî * Kyrgyzcha * Lezgi * Latina * Latviesu * Lëtzebuergesch * Lietuviu * Lingála * Magyar * Malagasy * ®²¯¾³ * Bahasa Melayu * ¼º¬¬¬ * Nahuatl * Nederlands * Nedersaksies * ¨ª¾² * ¥¬ * Norsk bokmål * Norsk nynorsk * Nouormand * Occitan * ª°¾¬ * ¶¶ * Polski * Português * Româna * Runa Simi * Russkij * Scots * Shqip * Sicilianu * Simple English * Slovencina * Slovenscina * Soomaaliga * Srpski / srpski * Suomi * Svenska * Tagalog * ¤®¿´ * Tatarcha/tatarça * ¤² * Türkçe * Ukrayins'ka * a+r+d+w+ * Vèneto * Tie>'ng Vie>-.t * Winaray * J+J+iD+J+Sh * Yorùbá * µ * Zemaiteska * ­ * Edit links * This page was last modified on 15 March 2013 at 20:34. * Text is available under the Creative Commons Attribution-ShareAlike License; 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