Lightning#Downward leader formation for negative CG lightning

Three primary forms of lightning are distinguished by where they occur:{{cite web |url=https://www.weather.gov/media/pah/WeatherEducation/lightningsafety.pdf |title=Severe Weather Safety Guide |publisher=National Weather Service |date=2022}}{{cite web |url=https://www.fastfactsforkids.com/weather-facts/lightning-facts-for-kids |title=Lightning Facts |publisher=Fast Facts for Kids |date=2022 |access-date=July 27, 2022 |archive-date=September 28, 2022 |archive-url=https://web.archive.org/web/20220928090650/https://www.fastfactsforkids.com/weather-facts/lightning-facts-for-kids |url-status=dead }}

• {{em|Intra-cloud}} (IC) or {{em|in-cloud}} — Within a single thundercloud
• {{em|Cloud-to-cloud}} (CC) or {{em|inter-cloud}} — Between two clouds
• {{em|Cloud-to-ground}} (CG) — Between a cloud and the ground, in which case it is referred to as a lightning strike.

Many other observational variants are recognized, including: volcanic lightning, which can occur during volcanic eruptions; "heat lightning", which can be seen from a great distance but not heard; dry lightning, which can cause forest fires; and ball lightning, which is rarely observed scientifically.

The most direct effects of lightning on humans occur as a result of cloud-to-ground lightning, even though intra-cloud and cloud-to-cloud are more common. Intra-cloud and cloud-to-cloud lightning indirectly affect humans through their influence on atmospheric chemistry.

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.

File:Lightning strikes in slow motion (240fps) in Muurame, Finland.webm

{{em|Cloud-to-ground}} (CG) lightning is a lightning discharge between a thundercloud and the ground. It is initiated by a stepped leader moving down from the cloud, which is met by a streamer moving up from the ground.

CG is the least common, but best understood of all types of lightning. It is easier to study scientifically because it terminates on a physical object, namely the ground, and lends itself to being measured by instruments on the ground. Of the three primary types of lightning, it poses the greatest threat to life and property, since it terminates on the ground or "strikes".

The overall discharge, termed a flash, is composed of a number of processes such as preliminary breakdown, stepped leaders, connecting leaders, return strokes, dart leaders, and subsequent return strokes.{{cite book |chapter=Mechanism of the Lightning Flash |title=The Lightning Flash |edition=2nd |editor-first=V.|editor-last=Cooray |publisher=Institution of Engineering and Technology |location=London |year=2014 |pages=119–229}} The conductivity of the electrical ground, be it soil, fresh water, or salt water, may affect the lightning discharge rate and thus visible characteristics.{{cite magazine |last=Jones|first=Nicola |title=Salty Seas Make Lightning Brighter |url=https://hakaimagazine.com/news/salty-seas-make-lightning-brighter |access-date=January 11, 2021 |magazine=Smithsonian |date=January 4, 2021}}

Cloud-to-ground (CG) lightning is either positive or negative, as defined by the direction of the conventional electric current between cloud and ground. Most CG lightning is negative, meaning that a negative charge is transferred (electrons flow) downwards to ground along the lightning channel (conventionally speaking they flow from the ground up to the cloud). The reverse happens in a positive CG flash, where electrons travel upward along the lightning channel, while also a positive charge is transferred downward to the ground (conventionally speaking this would be the opposite).

Positive lightning is less common than negative lightning and on average makes up less than 5% of all lightning strikes.{{cite web |title=NWS JetStream – The Positive and Negative Side of Lightning |publisher=National Oceanic and Atmospheric Administration |url=https://srh.noaa.gov/jetstream/lightning/positive.htm |access-date=September 25, 2007 |url-status=live |archive-url=https://web.archive.org/web/20070705205815/http://www.srh.noaa.gov/jetstream/lightning/positive.htm |archive-date=July 5, 2007 | df = mdy-all }}

File: Anvil-to-ground lightning.jpg and drive a bolt of plasma through the cloud directly to the ground. They are commonly referred to as positive flashes, despite the fact that they are usually negative in polarity.]]

There are a number of mechanisms theorized to result in the formation of positive lightning.{{cite journal |title=Positive lightning: An overview, new observations, and inferences |journal=Journal of Geophysical Research: Atmospheres |volume=117 |issue=D8 |year=2012 |last1=Nag|first1=Amitabh |last2=Rakov|first2=Vladimir A. |pages= |bibcode=2012JGRD..117.8109N |doi=10.1029/2012JD017545 |doi-access=free}} These are mainly based on movement or intensification of charge centres in the cloud. Such changes in cloud charging may come about as a result of variations in vertical wind shear or precipitation, or dissipation of the storm. Positive flashes may also result from certain behaviour of in-cloud discharges, e.g. breaking off or branching from existing flashes.

Positive lightning strikes tend to be much more intense than their negative counterparts. An average bolt of negative lightning creates an electric current of 30,000 amperes (30 kA), transferring a total 15 C (coulombs) of electric charge and 1 gigajoule of energy. Large bolts of positive lightning can create up to 120 kA and transfer 350 C.Hasbrouck, Richard. [https://llnl.gov/str/pdfs/05_96.1.pdf Mitigating Lightning Hazards] {{webarchive|url=https://web.archive.org/web/20131005005230/https://www.llnl.gov/str/pdfs/05_96.1.pdf |date=October 5, 2013 }}, Science & Technology Review May 1996. Retrieved on April 26, 2009. The average positive ground flash has roughly double the peak current of a typical negative flash, and can produce peak currents up to 400 kA and charges of several hundred coulombs.V. A. Rakov, M. A. Uman, Positive and bipolar lightning discharges to ground, in: Light. Phys. Eff., Cambridge University Press, 2003: pp. 214–240{{cite book |first1=U. A.|last1=Bakshi |first2=M. V.|last2=Bakshi |title=Power System – II |url=https://books.google.com/books?id=oOj4NjQ8xGQC&pg=SA12-PA5 |date=January 1, 2009 |publisher=Technical Publications |isbn=978-81-8431-536-3 |page=12 |url-status=live |archive-url=https://web.archive.org/web/20170312135216/https://books.google.com/books?id=oOj4NjQ8xGQC&pg=SA12-PA5 |archive-date=March 12, 2017 }} Furthermore, positive ground flashes with high peak currents are commonly followed by long continuing currents, a correlation not seen in negative ground flashes.{{cite journal |doi=10.1029/2010JD014330 |title=High-speed video observations of positive lightning flashes to ground |journal=Journal of Geophysical Research: Atmospheres |volume=115 |issue=D24 |pages=201 |year=2010 |last1=Saba|first1=Marcelo M. F. |last2=Schulz|first2=Wolfgang |last3=Warner|first3=Tom A. |last4=Campos|first4=Leandro Z. S. |last5=Schumann|first5=Carina |last6=Krider|first6=E. Philip |last7=Cummins|first7=Kenneth L. |last8=Orville|first8=Richard E. |bibcode=2010JGRD..11524201S |s2cid=129809543 |doi-access=free}}

As a result of their greater power, positive lightning strikes are considerably more dangerous than negative strikes.{{citation needed|date=January 2025}} Positive lightning produces both higher peak currents and longer continuing currents, making them capable of heating surfaces to much higher levels which increases the likelihood of a fire being ignited. The long distances positive lightning can propagate through clear air explains why they are known as "bolts from the blue", giving no warning to observers.

Positive lightning has also been shown to trigger the occurrence of upward lightning flashes from the tops of tall structures and is largely responsible for the initiation of sprites several tens of kilometers above ground level. Positive lightning tends to occur more frequently in winter storms, as with thundersnow, during intense tornadoes{{cite journal|author1=Perez, Antony H. |author2=Wicker, Louis J. |author3=Richard E. Orville |title=Characteristics of Cloud-to-Ground Lightning Associated with Violent Tornadoes|journal=Weather Forecast.|volume=12|issue=3|pages=428–37|doi=10.1175/1520-0434(1997)012<0428:COCTGL>2.0.CO;2|bibcode = 1997WtFor..12..428P|year=1997 |doi-access=free}} and in the dissipation stage of a thunderstorm.{{cite web

| url = http://thunder.nsstc.nasa.gov/primer/primer2.html|title = A Lightning Primer – Characteristics of a Storm |access-date = February 8, 2009 |author1=Christian, Hugh J. |author2=McCook, Melanie A. |work =NASA | url-status = dead|archive-url=https://web.archive.org/web/20160305002214/http://thunder.nsstc.nasa.gov/primer/primer2.html |archive-date=March 5, 2016}} Huge quantities of extremely low frequency (ELF) and very low frequency (VLF) radio waves are also generated.{{cite journal | last1 = Boccippio | first1 = DJ | title = Sprites, ELF Transients, and Positive Ground Strokes | journal = Science | volume = 269 | pages = 1088–1091 |date=August 1995 | doi = 10.1126/science.269.5227.1088 | pmid = 17755531 | last2 = Williams | first2 = ER | last3 = Heckman | first3 = SJ | last4 = Lyons | first4 = WA | last5 = Baker | first5 = IT | last6 = Boldi | first6 = R | issue = 5227 | bibcode = 1995Sci...269.1088B | s2cid = 8840716 }}

Contrary to popular belief, positive lightning flashes do not necessarily originate from the anvil or the upper positive charge region and strike a rain-free area outside of the thunderstorm. This belief is based on the outdated idea that lightning leaders are unipolar and originate from their respective charge region.{{citation needed|date=May 2021}} Despite the popular misconception that flashes originating from the anvil are positive, due to them seemingly originating from the positive charge region, observations have shown that these are in fact negative flashes. They begin as IC flashes within the cloud, the negative leader then exits the cloud from the positive charge region before propagating through clear air and striking the ground some distance away.{{cite journal|doi=10.1029/2011JD016890|title=Lightning morphology and impulse charge moment change of high peak current negative strokes|journal=Journal of Geophysical Research: Atmospheres|volume=117|issue=D4|year=2012|last1=Lu|first1=Gaopeng|last2=Cummer|first2=Steven A|last3=Blakeslee|first3=Richard J|last4=Weiss|first4=Stephanie|last5=Beasley|first5=William H|pages=n/a|bibcode=2012JGRD..117.4212L|citeseerx=10.1.1.308.9842}}{{cite journal|doi=10.1038/ngeo162|title=Upward electrical discharges from thunderstorms|journal=Nature Geoscience|volume=1|issue=4|page=233|year=2008|last1=Krehbiel|first1=Paul R|last2=Riousset|first2=Jeremy A|last3=Pasko|first3=Victor P|last4=Thomas|first4=Ronald J|last5=Rison|first5=William|last6=Stanley|first6=Mark A|last7=Edens|first7=Harald E|bibcode=2008NatGe...1..233K|s2cid=8753629}}

Lightning discharges may occur between areas of cloud without contacting the ground. When it occurs between two separate clouds, it is known as {{em|cloud-to-cloud}} (CC) or {{em|inter-cloud}} lightning; when it occurs between areas of differing electric potential within a single cloud, it is known as {{em|intra-cloud}} (IC) lightning. IC lightning is the most frequently occurring type.

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

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

File:Ligtning new delhi view 1.GIF|Branching of cloud to cloud lightning, New Delhi, India.

File:Cloud to cloud lightning strike.jpg|Multiple paths of cloud-to-cloud lightning, Swifts Creek, Australia.

File:Baltic thunder.jpg|Intra-clouds lightning over the Baltic Sea.

File:CC lightning, Albury NSW.JPG|Cloud-to-cloud lightning, Albury, Australia

The processes involved in lightning formation fall into the following categories:

1. Large-scale atmospheric phenomena in which charge separation can occur (e.g. storm)
2. Microscopic and macroscopic processes that result in charge separation
3. Establishment of an electric field
4. Discharge through a lightning channel

Lightning primarily occurs when warm air is mixed with colder air masses,{{Cite book|url=https://books.google.com/books?id=g1foWWN5odwC&q=Lightning+occurs+when+warm+air+is+mixed+with+colder+air+masses&pg=PA90|title=Sprites, Elves and Intense Lightning Discharges|last1=Füllekrug|first1=Martin|last2=Mareev|first2=Eugene A.|last3=Rycroft|first3=Michael J.|date=May 1, 2006|publisher=Springer Science & Business Media|isbn=9781402046285|url-status=live|archive-url=https://web.archive.org/web/20171104190958/https://books.google.com/books?id=g1foWWN5odwC&pg=PA90&dq=Lightning+occurs+when+warm+air+is+mixed+with+colder+air+masses&hl=en&sa=X&ved=0ahUKEwiV44XT9uXUAhVJ7mMKHb3pBUoQ6AEIMDAC#v=onepage&q=Lightning%20occurs%20when%20warm%20air%20is%20mixed%20with%20colder%20air%20masses&f=false|archive-date=November 4, 2017|bibcode=2006seil.book.....F}} resulting in atmospheric disturbances necessary for polarizing the atmosphere.{{cite book | editor = Hans Volland | date = 1995 | title = Handbook of Atmospheric Electrodynamics | publisher = CRC Press | page = 204 | isbn = 978-0-8493-8647-3 | url = https://books.google.com/books?id=MNPPh7B3WTIC|author1=Rinnert, K. |chapter=9: Lighting Within Planetary Atmospheres|quote=The requirements for the production of lightning within an atmosphere are the following: (1) a sufficient abundance of appropriate material for electrification, (2) the operation of a microscale electrification process to produce classes of particles with different signs of charge and (3) a mechanism to separate and to accumulate particles according to their charge.}} The disturbances result in storms, and when those storms also result in lightning and thunder, they are called a thunderstorm.

Lightning can also occur during dust storms, forest fires, tornadoes, volcanic eruptions, and even in the cold of winter, where the lightning is known as thundersnow.[http://news.nationalgeographic.com/news/2010/02/100203-volcanoes-lightning/ New Lightning Type Found Over Volcano?] {{webarchive|url=https://web.archive.org/web/20100209015048/http://news.nationalgeographic.com/news/2010/02/100203-volcanoes-lightning/ |date=February 9, 2010 }}. News.nationalgeographic.com (February 2010). Retrieved on June 23, 2012.{{cite web|url=http://hvo.wr.usgs.gov/volcanowatch/1998/98_06_11.html|title=Bench collapse sparks lightning, roiling clouds|access-date=October 7, 2012|publisher=United States Geological Survey|date=June 11, 1998|work=Volcano Watch|url-status=live|archive-url=https://web.archive.org/web/20120114172155/http://hvo.wr.usgs.gov/volcanowatch/1998/98_06_11.html|archive-date=January 14, 2012}} Hurricanes typically generate some lightning, mainly in the rainbands as much as {{convert|160|km|mi|abbr=on}} from the center.Pardo-Rodriguez, Lumari (Summer 2009) [http://nldr.library.ucar.edu/repository/assets/soars/SOARS-000-000-000-193.pdf Lightning Activity in Atlantic Tropical Cyclones: Using the Long-Range Lightning Detection Network (LLDN)] {{webarchive|url=https://web.archive.org/web/20130309085405/http://nldr.library.ucar.edu/repository/assets/soars/SOARS-000-000-000-193.pdf |date=March 9, 2013 }}. MA Climate and Society, Columbia University Significant Opportunities in Atmospheric Research and Science Program.[https://science.nasa.gov/science-news/science-at-nasa/2006/09jan_electrichurricanes/ Hurricane Lightning] {{webarchive|url=https://web.archive.org/web/20170815013425/https://science.nasa.gov/science-news/science-at-nasa/2006/09jan_electrichurricanes/ |date=August 15, 2017 }}, NASA, January 9, 2006.[http://www.unidata.ucar.edu/committees/polcom/2009spring/statusreports/BusingerS09.pdf The Promise of Long-Range Lightning Detection in Better Understanding, Nowcasting, and Forecasting of Maritime Storms] {{webarchive|url=https://web.archive.org/web/20130309085405/http://www.unidata.ucar.edu/committees/polcom/2009spring/statusreports/BusingerS09.pdf |date=March 9, 2013 }}. Long Range Lightning Detection Network

Intense forest fires, such as those seen in the 2019–20 Australian bushfire season, can create their own weather systems that can produce lightning (also called Fire Lightning) and other weather phenomena.{{Cite news |url=https://www.abc.net.au/news/2018-11-28/bushfire-storms-can-spark-fire-tornadoes-dry-lightning-and-more/10561832 |author=Ceranic, Irena |title=Fire tornadoes and dry lightning are just the start of the nightmare when a bushfire creates its own storm |date=November 28, 2020 |work=ABC News |publisher=Australian Broadcasting Corporation}} Intense heat from a fire causes air to rapidly rise within the smoke plume, causing the formation of pyrocumulonimbus clouds. Cooler air is drawn in by this turbulent, rising air, helping to cool the plume. The rising plume is further cooled by the lower atmospheric pressure at high altitude, allowing the moisture in it to condense into cloud. Pyrocumulonimbus clouds form in an unstable atmosphere. These weather systems can produce dry lightning, fire tornadoes, intense winds, and dirty hail.

As well as the thermodynamic and dynamic conditions of the atmosphere, aerosol (e.g. dust or smoke) composition is thought to influence the frequency of lightning flashes in a storm.{{cite journal |last1=Wang |first1=Qianqian |last2=Li |first2=Zhanqing |last3=Guo |first3=Jianping |last4=Zhao |first4=Chuanfeng |last5=Cribb |first5=Maureen |title=The climate impact of aerosols on the lightning flash rate: is it detectable from long-term measurements? |journal=Atmospheric Chemistry and Physics |date=6 September 2018 |volume=18 |issue=17 |pages=12797–12816 |doi=10.5194/acp-18-12797-2018|doi-access=free |bibcode=2018ACP....1812797W }} A specific example of this is that relatively high lightning frequency is seen along ship tracks.{{cite journal |last1=Thornton |first1=Joel A. |last2=Virts |first2=Katrina S. |last3=Holzworth |first3=Robert H. |last4=Mitchell |first4=Todd P. |title=Lightning enhancement over major oceanic shipping lanes |journal=Geophysical Research Letters |date=16 September 2017 |volume=44 |issue=17 |pages=9102–9111 |doi=10.1002/2017GL074982|doi-access=free |bibcode=2017GeoRL..44.9102T }}

Airplane contrails have also been observed to influence lightning to a small degree. The water vapor-dense contrails of airplanes may provide a lower resistance pathway through the atmosphere having some influence upon the establishment of an ionic pathway for a lightning flash to follow.Uman (1986) Ch. 4, pp. 26–34. Rocket exhaust plumes provided a pathway for lightning when it was witnessed striking the Apollo 12 rocket shortly after takeoff.

Thermonuclear explosions, by providing extra material for electrical conduction and a very turbulent localized atmosphere, have been seen triggering lightning flashes within the mushroom cloud. In addition, intense gamma radiation from large nuclear explosions may develop intensely charged regions in the surrounding air through Compton scattering. The intensely charged space charge regions create multiple clear-air lightning discharges shortly after the device detonates.{{Cite journal|date= 1987 | title= An empirical study of the nuclear explosion-induced lightning seen on IVY-MIKE | journal= Journal of Geophysical Research | volume= 92 | issue= D5 | pages= 5696–5712| bibcode=1987JGR....92.5696C | doi= 10.1029/JD092iD05p05696| author= Colvin, J. D. | last2= Mitchell | first2= C. K. | last3= Greig | first3= J. R. | last4= Murphy | first4= D. P. | last5= Pechacek | first5= R. E. | last6= Raleigh | first6= M.}}

Some high energy cosmic rays produced by supernovas as well as solar particles from the solar wind, enter the atmosphere and electrify the air, which may create pathways for lightning channels.{{cite web|url=http://www.iop.org/news/14/may/page_63245.html |title=High-speed solar winds increase lightning strikes on Earth |publisher=Iop.org |date=May 15, 2014 |access-date=May 19, 2014}}

File: Understanding Lightning - Figure 1 - Cloud Charging Area.gif

File:Graupel animation 3a.gif

File:Charged cloud animation 4a.gif

The details of the charging process are still being studied by scientists, but there is general agreement on some of the basic concepts of thunderstorm charge separation, also known as electrification. Electrification can be by the triboelectric effect leading to electron or ion transfer between colliding bodies.

The main charging area in a thunderstorm occurs in the central part of the storm where air is moving upward rapidly (updraft) and temperatures range from {{convert|-15|to|-25|C|F}}; see Figure 1. In that area, the combination of temperature and rapid upward air movement produces a mixture of super-cooled cloud droplets (small water droplets below freezing), small ice crystals, and graupel (soft hail). The updraft carries the super-cooled cloud droplets and very small ice crystals upward. At the same time, the graupel, which is considerably larger and denser, tends to fall or be suspended in the rising air.{{cite web|url=http://www.lightningsafety.noaa.gov/science/science_electrication.htm |title=NWS Lightning Safety: Understanding Lightning: Thunderstorm Electrification |publisher=National Oceanic and Atmospheric Administration|access-date=November 25, 2016|url-status=dead|archive-url=https://web.archive.org/web/20161130080723/http://www.lightningsafety.noaa.gov/science/science_electrication.htm |archive-date=November 30, 2016}} {{PD-notice}}

The differences in the movement of the cloud particles cause collisions to occur. When the rising ice crystals collide with graupel, the ice crystals become positively charged and the graupel becomes negatively charged; see Figure 2. The updraft carries the positively charged ice crystals upward toward the top of the storm cloud. The larger and denser graupel is either suspended in the middle of the thunderstorm cloud or falls toward the lower part of the storm. Typically, the upper part of the thunderstorm cloud becomes positively charged while the middle to lower part of the thunderstorm cloud becomes negatively charged.{{cite web |title=Lecture 11 - Thunderstorm electrification |url=http://www.atmo.arizona.edu/students/courselinks/spring13/atmo589/ATMO489_online/lecture_11/lect11_cloud_electrification.html |website=www.atmo.arizona.edu |access-date=31 January 2025}} The above process of charge separation as a result of cloud particle collisions is normally referred to as the non-inductive charging mechanism.{{cite journal |last1=Yair |first1=Y. |title=Charge Generation and Separation Processes |journal=Space Science Reviews |date=June 2008 |volume=137 |issue=1–4 |pages=119–131 |doi=10.1007/s11214-008-9348-x|bibcode=2008SSRv..137..119Y }}

The upward motions within the storm and winds at higher levels in the atmosphere tend to cause the small ice crystals (and positive charge) in the upper part of the thunderstorm cloud to spread out horizontally some distance from the thunderstorm cloud base. This part of the thunderstorm cloud is called the anvil. While this is the main charging process for the thunderstorm cloud, some of these charges can be redistributed by air movements within the storm (updrafts and downdrafts). In addition, there is a small but important positive charge buildup near the bottom of the thunderstorm cloud due to the precipitation and warmer temperatures. The positive-negative-positive charge regions commonly occur in mature thunderstorms, and referred to as the tripolar charge structure.

There are also other charging processes that may play a role in thunderstorms, but are generally thought to be less important. An inductive charging mechanism has been studied, and would arise from the polarisation of cloud droplets in the presence of the fair-weather electric field. It has also been stated that uncharged, colliding water-drops can become charged because of charge transfer between them (as aqueous ions) in an electric field as would exist in a thunderstorm.{{cite journal | last1=Jennings | first1=S. G. | last2=Latham | first2=J. | title=The charging of water drops falling and colliding in an electric field | journal=Archiv für Meteorologie, Geophysik und Bioklimatologie, Serie A | publisher=Springer Science and Business Media LLC | volume=21 | issue=2–3 | year=1972 | doi=10.1007/bf02247978 | pages=299–306| bibcode=1972AMGBA..21..299J | s2cid=118661076 }}

The induced separation of charge in pure liquid water has been known since the 1840s as has the electrification of pure liquid water by the triboelectric effect.Francis, G. W., "Electrostatic Experiments" Oleg D. Jefimenko, Editor, Electret Scientific Company, Star City, 2005 William Thomson (Lord Kelvin) demonstrated that charge separation in water occurs in the usual electric fields at the Earth's surface and developed a continuous electric field measuring device using that knowledge.{{cite journal |last1=Aplin |first1=K. L. |last2=Harrison |first2=R. G. |title=Lord Kelvin's atmospheric electricity measurements |journal=History of Geo- and Space Sciences |date=September 3, 2013 |volume=4 |issue=2 |pages=83–95 |doi=10.5194/hgss-4-83-2013|arxiv=1305.5347 |bibcode=2013HGSS....4...83A |s2cid=9783512 |doi-access=free }} The physical separation of charge into different regions using liquid water was demonstrated by Kelvin with the Kelvin water dropper. The most likely charge-carrying species were considered to be the aqueous hydrogen ion and the aqueous hydroxide ion.{{cite journal |last1=Desmet |first1=S |last2=Orban |first2=F |last3=Grandjean |first3=F |title=On the Kelvin electrostatic generator |journal=European Journal of Physics |date=April 1, 1989 |volume=10 |issue=2 |pages=118–122 |doi=10.1088/0143-0807/10/2/008|bibcode=1989EJPh...10..118D |s2cid=121840275 }} An electron is not stable in liquid water concerning a hydroxide ion plus dissolved hydrogen for the time scales involved in thunderstorms.Buxton, G. V., Greenstock, C. L., Helman, W. P. and Ross, A. B. "Critical Review of rate constants for reactions of hydrated electrons, hydrogen atoms and hydroxyl radicals (OH/O in aqueous solution." J. Phys. Chem. Ref. Data 17, 513–886 (1988). The electrical charging of solid water ice has also been considered. The charged species were again considered to be the hydrogen ion and the hydroxide ion.{{cite journal |last1=Dash |first1=J G |last2=Wettlaufer |first2=J S |title=The surface physics of ice in thunderstorms |journal=Canadian Journal of Physics |date=January 1, 2003 |volume=81 |issue=1–2 |pages=201–207 |doi=10.1139/P03-011|bibcode=2003CaJPh..81..201D }}{{cite journal |last1=Dash |first1=J. G. |last2=Mason |first2=B. L. |last3=Wettlaufer |first3=J. S. |title=Theory of charge and mass transfer in ice-ice collisions |journal=Journal of Geophysical Research: Atmospheres |date=September 16, 2001 |volume=106 |issue=D17 |pages=20395–20402 |doi=10.1029/2001JD900109|bibcode=2001JGR...10620395D |doi-access=free }}

{{main|Thunderstorm}}

In order for an electrostatic discharge to occur, two preconditions are necessary: first, a sufficiently high potential difference between two regions of space must exist, and second, a high-resistance medium must obstruct the free, unimpeded equalization of the opposite charges. The atmosphere provides the electrical insulation, or barrier, that prevents free equalization between charged regions of opposite polarity. Meanwhile, a thunderstorm can provide the charge separation and aggregation in certain regions of the cloud.{{cite journal|doi=10.1175/1520-0450(1993)032<0642:AROTEP>2.0.CO;2|volume=32|title=A Review of Thunderstorm Electrification Processes |last1=Saunders|first1=C. P. R.|journal=Journal of Applied Meteorology |issue=4 |pages=642–55|bibcode=1993JApMe..32..642S |year=1993|doi-access=free}}

When the local electric field exceeds the dielectric strength of damp air (about 3 MV/m), electrical discharge results in a strike, often followed by commensurate discharges branching from the same path. Mechanisms that cause the charges to build up to lightning are still a matter of scientific investigation.{{cite web|url=https://www.pbs.org/wnet/savageplanet/03deadlyskies/01lforms/indexmid.html|title=How Lightning Forms|access-date=September 21, 2007|publisher=Public Broadcasting System|author=Fink, Micah|work=PBS.org|url-status=live|archive-url=https://web.archive.org/web/20070929174806/http://www.pbs.org/wnet/savageplanet/03deadlyskies/01lforms/indexmid.html|archive-date=September 29, 2007}}{{cite web|url=http://www.lightningsafety.noaa.gov/science.htm|title=Lightning Safety|access-date=September 21, 2007|publisher=National Weather Service|date=2007|author=National Weather Service|url-status=dead|archive-url=https://web.archive.org/web/20071007110300/http://www.lightningsafety.noaa.gov/science.htm|archive-date=October 7, 2007}} A 2016 study confirmed dielectric breakdown is involved.{{Cite journal|last1=Rison|first1=William|last2=Krehbiel|first2=Paul R.|last3=Stock|first3=Michael G.|last4=Edens|first4=Harald E.|last5=Shao|first5=Xuan-Min|last6=Thomas|first6=Ronald J.|last7=Stanley|first7=Mark A.|last8=Zhang|first8=Yang|date=February 15, 2016|title=Observations of narrow bipolar events reveal how lightning is initiated in thunderstorms|journal=Nature Communications|volume=7|issue=1|pages=10721|doi=10.1038/ncomms10721|pmid=26876654|pmc=4756383|bibcode=2016NatCo...710721R|doi-access=free}} Lightning may be caused by the circulation of warm moisture-filled air through electric fields.Uman (1986) p. 61. Ice or water particles then accumulate charge as in a Van de Graaff generator.Rakov and Uman, p. 84.

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

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

The charge carrier in lightning is mainly electrons in a plasma.{{Cite book|last=Uman|first=Martin|title=All About Lightning|publisher=Dover|year=1986|isbn=978-0-486-25237-7|location=New York|pages=74}} The process of going from charge as ions (positive hydrogen ion and negative hydroxide ion) associated with liquid water or solid water to charge as electrons associated with lightning must involve some form of electro-chemistry, that is, the oxidation and/or the reduction of chemical species.{{cite journal |last1=Witzke |first1=Megan |last2=Rumbach |first2=Paul |last3=Go |first3=David B |last4=Sankaran |first4=R Mohan |title=Evidence for the electrolysis of water by atmospheric-pressure plasmas formed at the surface of aqueous solutions |journal=Journal of Physics D |date=November 7, 2012 |volume=45 |issue=44 |pages=442001 |doi=10.1088/0022-3727/45/44/442001|bibcode=2012JPhD...45R2001W |s2cid=98547405 }}

The best-studied and understood form of lightning is cloud to ground (CG) lightning. Although more common, intra-cloud (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 of lightning striking the same point repeatedly and consistently, scientific inquiry is difficult even in areas of high CG frequency.

File: Lightning formation.gif

File:Leaderlightnig.gif

In a process not well understood, a bidirectional channel of ionized air, called a "leader", is initiated between oppositely-charged regions in a thundercloud. Leaders are electrically conductive channels of ionized gas that propagate through, or are otherwise attracted to, regions with a charge opposite of that of the leader tip. The negative end of the bidirectional leader fills a positive charge region, also called a well, inside the cloud while the positive end fills a negative charge well. Leaders often split, forming branches in a tree-like pattern.Ultraslow-motion video of stepped leader propagation: [http://www.ztresearch.com/ ztresearch.com] {{webarchive|url=https://web.archive.org/web/20100413125231/http://www.ztresearch.com/ |date=April 13, 2010 }} In addition, negative and some positive leaders travel in a discontinuous fashion, in a process called "stepping". The resulting jerky movement of the leaders can be readily observed in slow-motion videos of lightning flashes.

It is possible for one end of the leader to fill the oppositely-charged well entirely while the other end is still active. When this happens, the leader end which filled the well may propagate outside of the thundercloud and result in either a cloud-to-air flash or a cloud-to-ground flash. In a typical cloud-to-ground flash, a bidirectional leader initiates between the main negative and lower positive charge regions in a thundercloud. The weaker positive charge region is filled quickly by the negative leader which then propagates toward the inductively-charged ground.

The positively and negatively charged leaders proceed in opposite directions, positive upwards within the cloud and negative towards the earth. Both ionic channels proceed, in their respective directions, in a number of successive spurts. Each leader "pools" ions at the leading tips, shooting out one or more new leaders, momentarily pooling again to concentrate charged ions, then shooting out another leader. The negative leader continues to propagate and split as it heads downward, often speeding up as it gets closer to the Earth's surface.

About 90% of ionic channel lengths between "pools" are approximately {{convert|45|m|ft|abbr=on}} in length.Goulde, R.H. (1977) "The lightning conductor", pp. 545–576 in Lightning Protection, R.H. Golde, Ed., Lightning, Vol. 2, Academic Press. The establishment of the ionic channel takes a comparatively long amount of time (hundreds of milliseconds) in comparison to the resulting discharge, which occurs within a few dozen microseconds. The electric current needed to establish the channel, measured in the tens or hundreds of amperes, is dwarfed by subsequent currents during the actual discharge.

Initiation of the lightning leader is not well understood. The electric field strength within the thundercloud is not typically large enough to initiate this process by itself.{{cite journal|doi=10.1007/s11214-008-9338-z|title=Charge Structure and Dynamics in Thunderstorms|date=2008|last1=Stolzenburg|first1=Maribeth|last2=Marshall|first2=Thomas C.|journal=Space Science Reviews|volume=137|issue=1–4|page=355|bibcode = 2008SSRv..137..355S |s2cid=119997418}} Many hypotheses have been proposed. One hypothesis postulates that showers of relativistic electrons are created by cosmic rays and are then accelerated to higher velocities via a process called runaway breakdown. As these relativistic electrons collide and ionize neutral air molecules, they initiate leader formation. Another hypothesis involves locally enhanced electric fields being formed near elongated water droplets or ice crystals.{{cite journal|doi=10.1029/2007JD009036|title=A brief review of the problem of lightning initiation and a hypothesis of initial lightning leader formation|date=2008|last1=Petersen|first1=Danyal|last2=Bailey|first2=Matthew|last3=Beasley|first3=William H.|last4=Hallett|first4=John|journal=Journal of Geophysical Research|volume=113|issue=D17|pages=D17205|bibcode = 2008JGRD..11317205P }} Percolation theory, especially for the case of biased percolation,{{cite journal|doi=10.1103/PhysRevE.81.011102|pmid=20365318|title=Biased percolation on scale-free networks|date=2010|last1=Hooyberghs|first1=Hans|last2=Van Schaeybroeck|first2=Bert|last3=Moreira|first3=André A.|last4=Andrade|first4=José S.|last5=Herrmann|first5=Hans J.|last6=Indekeu|first6=Joseph O.|journal=Physical Review E|volume=81|issue=1|page=011102|bibcode = 2010PhRvE..81a1102H |arxiv = 0908.3786 |s2cid=7872437}} {{clarify| what does 'biased percolation' mean?|date= July 2013}} describes random connectivity phenomena, which produce an evolution of connected structures similar to that of lightning strikes. A streamer avalanche model{{Cite journal|last1=Griffiths|first1=R. F.|last2=Phelps|first2=C. T.|date=1976|title=A model for lightning initiation arising from positive corona streamer development|journal=Journal of Geophysical Research|volume=81|issue=21|pages=3671–3676|doi=10.1029/JC081i021p03671|bibcode=1976JGR....81.3671G}} has recently been favored by observational data taken by LOFAR during storms.{{Cite journal|last1=Sterpka|first1=Christopher|last2=Dwyer|first2=J|last3=Liu|first3=N|last4=Hare|first4=B M|last5=Scholten|first5=O|last6=Buitink|first6=S|last7=Ter Veen|first7=S|last8=Nelles|first8=A|date=November 24, 2021|title=The Spontaneous Nature of Lightning Initiation Revealed|journal=Ess Open Archive ePrints |volume=105 |issue=23 |pages=GL095511 |doi=10.1002/essoar.10508882.1|bibcode=2021GeoRL..4895511S |s2cid=244646368|url=https://bib-pubdb1.desy.de/record/474239 |hdl=2066/242824|hdl-access=free}}{{Cite web|last=Lewton|first=Thomas|date=December 20, 2021|title=Detailed Footage Finally Reveals What Triggers Lightning|url=https://www.quantamagazine.org/radio-telescope-reveals-how-lightning-begins-20211220/|access-date=December 21, 2021|website=Quanta Magazine}}

File:Upwards streamer from pool cover.jpg

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.Kasemir, H. W. (1950) "Qualitative Übersicht über Potential-, Feld- und Ladungsverhaltnisse Bei einer Blitzentladung in der Gewitterwolke" (Qualitative survey of the potential, field and charge conditions during a lightning discharge in the thunderstorm cloud) in Das Gewitter (The Thunderstorm), H. Israel, ed., Leipzig, Germany: Akademische Verlagsgesellschaft.Ruhnke, Lothar H. (June 7, 2007) "[https://archive.today/20110611231459/http://www.physicstoday.org/obits/notice_157.shtml Death notice: Heinz Wolfram Kasemir]". Physics Today.{{cite web |last1=Stephan |first1=Karl |title=The Man Who Understood Lightning |url=https://blogs.scientificamerican.com/guest-blog/the-man-who-understood-lightning/ |publisher=Scientific American |access-date=June 26, 2020 |date=March 3, 2016}}

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

Once a downward leader connects to an available upward leader, a process referred to as attachment, a low-resistance path is formed and discharge may occur. Photographs have been taken in 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. High-speed videos can show the attachment process in progress.{{Cite journal |doi = 10.1002/2017GL072796|title = Lightning attachment process to common buildings|journal = Geophysical Research Letters|volume = 44|issue = 9|pages = 4368–4375|year = 2017|last1 = Saba|first1 = M. M. F.|last2 = Paiva|first2 = A. R.|last3 = Schumann|first3 = C.|last4 = Ferro|first4 = M. A. S.|last5 = Naccarato|first5 = K. P.|last6 = Silva|first6 = J. C. O.|last7 = Siqueira|first7 = F. V. C.|last8 = Custódio|first8 = D. M.|bibcode = 2017GeoRL..44.4368S|doi-access = free}}

{{redirect|Return stroke}}

File:Lightnings sequence 2 animation-wcag.gif, France.]]

Once a conductive channel bridges the air gap between the negative charge excess in the cloud and the positive surface charge excess below, there is a large drop in resistance across the lightning channel. Electrons accelerate rapidly as a result in a zone beginning at the point of attachment, which expands across the entire leader network at up to one third of the speed of light.{{cite book|url=https://books.google.com/books?id=DgHCAgAAQBAJ|title=The lightning discharge|access-date=September 1, 2020|publisher=Courier Corporation|author=Uman, M. A.| date=2001|isbn=9780486151984}} This is the "return stroke" and it is the most luminous and noticeable part of the lightning discharge.

A large electric charge flows along the plasma channel, from the cloud to the ground, neutralising the positive ground charge as electrons flow away from the strike point to the surrounding area. This huge surge of current creates large radial voltage differences along the surface of the ground. Called step potentials,{{citation needed|date=September 2020}} they are responsible for more injuries and deaths in groups of people or of other animals than the strike itself.Deamer, Kacey (August 30, 2016) [https://www.livescience.com/55916-why-reindeer-killed-by-lightning.html More Than 300 Reindeer Killed By Lightning: Here's Why]. Live Science Electricity takes every path available to it.{{cite web|title=The Path of Least Resistance|url=http://ecmweb.com/content/path-least-resistance|url-status=dead|archive-url=https://web.archive.org/web/20160104215214/http://ecmweb.com/content/path-least-resistance|archive-date=January 4, 2016|date=July 2001|access-date=January 9, 2016}}

Such step potentials will often cause current to flow through one leg and out another, electrocuting an unlucky human or animal standing near the point where the lightning strikes.

The electric current of the return stroke averages 30 kiloamperes for a typical negative CG flash, often referred to as "negative CG" lightning. In some cases, a ground-to-cloud (GC) lightning flash may originate from a positively charged region on the ground below a storm. These discharges normally originate from the tops of very tall structures, such as communications antennas. The rate at which the return stroke current travels has been found to be around 100,000 km/s (one-third of the speed of light).{{Cite journal | last1 = Idone | first1 = V. P. | last2 = Orville | first2 = R. E. | last3 = Mach | first3 = D. M. | last4 = Rust | first4 = W. D. | title = The propagation speed of a positive lightning return stroke | doi = 10.1029/GL014i011p01150 | journal = Geophysical Research Letters | volume = 14 | issue = 11 | page = 1150 | year = 1987 |bibcode = 1987GeoRL..14.1150I | url = https://zenodo.org/record/1231386 }} A typical cloud-to-ground lightning flash culminates in the formation of an electrically conducting plasma channel through the air in excess of {{convert|5|km|mi|abbr=on}} tall, from within the cloud to the ground's surface.Uman (1986) p. 81.

The massive flow of electric current occurring during the return stroke combined with the rate at which it occurs (measured in microseconds) rapidly superheats the completed leader channel, forming a highly electrically conductive plasma channel. The core temperature of the plasma during the return stroke may exceed {{convert|50,000|F|C|order=flip}},{{Cite web |last=US Department of Commerce |first=NOAA |title=Understanding Lightning: Thunder |url=https://www.weather.gov/safety/lightning-science-thunder#:~:text=The%20lightning%20discharge%20heats%20the,the%20surface%20of%20the%20sun |access-date=December 15, 2023 |website=www.weather.gov |language=EN-US}} causing it to radiate with a brilliant, blue-white color. Once the electric current stops flowing, the channel cools and dissipates over tens or hundreds of milliseconds, often disappearing as fragmented patches of glowing gas. The nearly instantaneous heating during the return stroke causes the air to expand explosively, producing a powerful shock wave which is heard as thunder.

High-speed videos (examined frame-by-frame) show that most negative CG lightning flashes are made up of 3 or 4 individual strokes, though there may be as many as 30.Uman (1986) Ch. 5, p. 41.

Each re-strike is separated by a relatively large amount of time, typically 40 to 50 milliseconds, as other charged regions in the cloud are discharged in subsequent strokes. Re-strikes often cause a noticeable "strobe light" effect.Uman (1986) pp. 103–110.

To understand why multiple return strokes utilize the same lightning channel, one needs to understand the behavior of positive leaders, which a typical ground flash effectively becomes following the negative leader's connection with the ground. Positive leaders decay more rapidly than negative leaders do. For reasons not well understood, bidirectional leaders tend to initiate on the tips of the decayed positive leaders in which the negative end attempts to re-ionize the leader network. These leaders, also called recoil leaders, usually decay shortly after their formation. When they do manage to make contact with a conductive portion of the main leader network, a return stroke-like process occurs and a dart leader travels across all or a portion of the length of the original leader. The dart leaders making connections with the ground are what cause a majority of subsequent return strokes.{{cite web |url=https://ztresearch.blog/education/ground-flashes/ |title=Ground Flashes |last=Warner |first=Tom |website=ZT Research |access-date=November 9, 2017|date=May 6, 2017 }}

Each successive stroke is preceded by intermediate dart leader strokes that have a faster rise time but lower amplitude than the initial return stroke. Each subsequent stroke usually re-uses the discharge channel taken by the previous one, but the channel may be offset from its previous position as wind displaces the hot channel.Uman (1986) Ch. 9, p. 78.

Since recoil and dart leader processes do not occur on negative leaders, subsequent return strokes very seldom utilize the same channel on positive ground flashes which are explained later in the article.

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

The rapidly changing currents also create electromagnetic pulses (EMPs) that radiate outward from the ionic channel. This is a characteristic of all electrical discharges. The radiated pulses rapidly weaken as their distance from the origin increases. However, if they pass over conductive elements such as power lines, communication lines, or metallic pipes, they may induce a current which travels outward to its termination. The surge current is inversely related to the surge impedance: the higher in impedance, the lower the current.{{Cite web|url=https://site.ieee.org/sas-pesias/files/2016/03/Lightning-Protection-and-Transient-Overvoltage_Rogerio-Verdolin.pdf|title=Lightning Protection and Transient Overvoltage}} This is the surge that, more often than not, results in the destruction of delicate electronics, electrical appliances, or electric motors. Devices known as surge protectors (SPD) or transient voltage surge suppressors (TVSS) attached in parallel with these lines can detect the lightning flash's transient irregular current, and, through alteration of its physical properties, route the spike to an attached earthing ground, thereby protecting the equipment from damage.

{{main|Distribution of lightning}}

File: Global Lightning Frequency.png's Optical Transient Detector depicting space-based sensors revealing the uneven distribution of worldwide lightning strikes]]

File:Megaflash of 477 miles.png to Louisiana, in the United States.{{citation |title=New WMO Certified Megaflash Lightning Extremes for Flash Distance (768 km) and Duration (17.01 seconds) Recorded from Space |author=Randall Cerveny |collaboration=WMO panel |doi=10.1175/BAMS-D-21-0254.1 |journal=Bulletin of the American Meteorological Society |date=February 1, 2022|hdl=2117/369605 |s2cid=246358397 |doi-access=free |hdl-access=free }}]]

Global monitoring indicates that lightning on Earth occurs at an average frequency of approximately 44 (± 5) times per second, equating to nearly 1.4 billion flashes per year.{{cite book|url=https://books.google.com/books?id=-mwbAsxpRr0C&pg=PA452|title=Encyclopedia of World Climatology|access-date=February 8, 2009|publisher=National Oceanic and Atmospheric Administration|author=Oliver, John E.| isbn=978-1-4020-3264-6|date=2005}} Median duration is 0.52 seconds{{cite journal |last1=Kákona |first1=Jakub |title=In situ ground-based mobile measurement of lightning events above central Europe |journal=Atmospheric Measurement Techniques|year=2023 |volume=16 |issue=2 |pages=547–561 |doi=10.5194/amt-16-547-2023 |bibcode=2023AMT....16..547K |s2cid=253187897 |doi-access=free }} made up from a number of much shorter flashes (strokes) of around 60 to 70 microseconds.{{cite web|url=http://hyperphysics.phy-astr.gsu.edu/hbase/electric/lightning2.html|title=Lightning|work=gsu.edu|access-date=December 30, 2015|url-status=dead|archive-url=https://web.archive.org/web/20160115043319/http://hyperphysics.phy-astr.gsu.edu/hbase/electric/lightning2.html|archive-date=January 15, 2016}} Occurrences are distributed unevenly across the planet with about 70% being over land in the tropics{{Cite book|url=https://books.google.com/books?id=5oZUAAAAMAAJ&q=70%25+of+lightning+occurs+in+tropics+on+land|title=Encyclopedia of atmospheric sciences|last1=Holton|first1=James R.|last2=Curry|first2=Judith A.|last3=Pyle|first3=J. A.|date=2003|publisher=Academic Press|isbn=9780122270901|url-status=live|archive-url=https://web.archive.org/web/20171104190958/https://books.google.com/books?id=5oZUAAAAMAAJ&q=70%25+of+lightning+occurs+in+tropics+on+land&dq=70%25+of+lightning+occurs+in+tropics+on+land&hl=en&sa=X&ved=0ahUKEwjq6bqvrbzUAhUC4GMKHRR6AUkQ6AEINzAF|archive-date=November 4, 2017}} where atmospheric convection is the greatest.

Many factors affect the frequency, distribution, strength and physical properties of a typical lightning flash in a particular region of the world. These factors include ground elevation, latitude, prevailing wind currents, relative humidity, and proximity to warm and cold bodies of water.{{citation needed|date=February 2025}}

Lightning is usually produced by cumulonimbus clouds, which have bases that are typically {{cvt|1|-|2|km}} above the ground and tops up to {{convert|15|km|mi|abbr=on}} in height.

File:LightningStrike240FPS.webm, Australia.]]

In general, CG lightning flashes account for only 25% of all total lightning flashes worldwide. The proportions of intra-cloud, cloud-to-cloud, and cloud-to-ground lightning may also vary by season at latitude.{{cite journal |last1=Price |first1=Colin |last2=Rind |first2=David |title=What determines the cloud-to-ground lightning fraction in thunderstorms? |journal=Geophysical Research Letters |date=1993 |volume=20 |issue=6 |pages=463–466 |doi=10.1029/93GL00226 |bibcode=1993GeoRL..20..463P }}{{cite journal |last1=Bandholnopparat |first1=K. |last2=Sato |first2=M. |last3=Adachi |first3=T. |last4=Ushio |first4=T. |last5=Takahashi |first5=Y. |title=Estimation of the IC to CG Ratio Using JEM-GLIMS and Ground-Based Lightning Network Data |journal=Journal of Geophysical Research: Atmospheres |date=2020 |volume=125 |issue=23 |pages=e2019JD032195 |doi=10.1029/2019JD032195 |bibcode=2020JGRD..12532195B }} In the tropics, where the freezing level is generally higher in the atmosphere, only 10% of lightning flashes are CG. At the latitude of Norway (around 60° North latitude), where the freezing elevation is lower, 50% of lightning is CG.{{cite web|url=https://science.nasa.gov/science-news/science-at-nasa/2001/ast05dec_1/|date=December 5, 2001|title=Where LightningStrikes|publisher=NASA Science. Science News.|access-date=July 5, 2010|url-status=dead|archive-url=https://web.archive.org/web/20100716173018/http://science.nasa.gov/science-news/science-at-nasa/2001/ast05dec_1/|archive-date=July 16, 2010}}Uman (1986) Ch. 8, p. 68.

File:Lighting barrage.jpg in August 2020]]

The place on Earth where lightning occurs most often is over Lake Maracaibo, wherein the Catatumbo lightning phenomenon produces 250 bolts of lightning a day.{{cite web |author1=R. I. Albrecht |author2=S. J. Goodman |author3=W. A. Petersen |author4=D. E. Buechler |author5=E. C. Bruning |author6=R. J. Blakeslee |author7=H. J. Christian |title=The 13 years of TRMM Lightning Imaging Sensor: From individual flash characteristics to decadal tendencies |url=https://ntrs.nasa.gov/api/citations/20110015779/downloads/20110015779.pdf |website=NASA Technical Reports Server |access-date=November 23, 2022}} This activity occurs on average, 297 days a year.Fischetti, M. (2016) [https://www.scientificamerican.com/article/the-world-s-top-lightning-hotspot-is-lake-maracaibo-in-venezuela/ Lightning Hotspots], Scientific American 314: 76 (May 2016) The second most lightning density is near the village of Kifuka in the mountains of the eastern Democratic Republic of the Congo,{{cite web|url=http://www.wondermondo.com/Countries/Af/CongoDR/SudKivu/Kifuka.htm|title=Kifuka – place where lightning strikes most often|access-date=November 21, 2010|publisher=Wondermondo|url-status=dead|archive-url=https://web.archive.org/web/20111001201900/http://www.wondermondo.com/Countries/Af/CongoDR/SudKivu/Kifuka.htm|archive-date=October 1, 2011|date=November 7, 2010}} where the elevation is around {{convert|975|m|ft|-2|abbr=on}}. On average, this region receives {{convert|158|/km2/years|/sqmi/years|adj=pre|lightning strikes}}.{{cite web|url=http://sos.noaa.gov/datasets/Atmosphere/lightning.html|archive-url=https://web.archive.org/web/20080330025304/http://sos.noaa.gov/datasets/Atmosphere/lightning.html|archive-date=March 30, 2008|title=Annual Lightning Flash Rate |access-date=February 8, 2009|publisher=National Oceanic and Atmospheric Administration}} Other lightning hotspots include Singapore{{cite web|url=http://app.nea.gov.sg/cms/htdocs/article.asp?pid=1203|archive-url=https://web.archive.org/web/20070927224804/http://app.nea.gov.sg/cms/htdocs/article.asp?pid=1203|archive-date=September 27, 2007|title=Lightning Activity in Singapore|access-date=September 24, 2007|publisher=National Environmental Agency|date=2002}} and Lightning Alley in Central Florida.{{cite web|url=http://www.nasa.gov/centers/kennedy/news/lightning_alley.html|title=Staying Safe in Lightning Alley|access-date=September 24, 2007|publisher=NASA|date=January 3, 2007|url-status=live|archive-url=https://web.archive.org/web/20070713041430/http://www.nasa.gov/centers/kennedy/news/lightning_alley.html|archive-date=July 13, 2007}}{{cite web|url=http://www.floridaenvironment.com/programs/fe00703.htm |title=Summer Lightning Ahead |access-date=September 24, 2007 |publisher=Florida Environment.com |date=2000 |author=Pierce, Kevin |url-status=dead |archive-url=https://web.archive.org/web/20071012160959/http://floridaenvironment.com/programs/fe00703.htm |archive-date=October 12, 2007 }}

According to the World Meteorological Organization, on April 29, 2020, a bolt 768 km (477.2 mi) long was observed in the southern U.S.—sixty km (37 mi) longer than the previous distance record (southern Brazil, October 31, 2018). A single flash in Uruguay and northern Argentina on June 18, 2020, lasted for 17.1 seconds—0.37 seconds longer than the previous record (March 4, 2019, also in northern Argentina).{{cite web |last1=Larson |first1=Nina |title=770-km US megaflash sets new lightning record |url=https://phys.org/news/2022-02-longest-lightning-miles-states.html |website=Phys.org |archive-url=https://web.archive.org/web/20220201111718/https://phys.org/news/2022-02-longest-lightning-miles-states.html |archive-date=February 1, 2022 |date=February 1, 2022 |url-status=live}}

Researchers at the University of Florida found that the final one-dimensional speeds of 10 flashes observed were between 1.0{{e|5}} and 1.4{{e|6}} m/s, with an average of 4.4{{e|5}} m/s.{{cite journal|last=Thomson|first=E. M.|author2=Uman, M. A. |author3=Beasley, W. H. |title=Speed and current for lightning stepped leaders near ground as determined from electric field records|journal=Journal of Geophysical Research|date=January 1985|volume=90|issue=D5|page=8136|doi=10.1029/JD090iD05p08136|bibcode=1985JGR....90.8136T}}

Lightning has been observed within the atmospheres of planets other than Earth, such as Jupiter, Saturn, and probably Uranus and Neptune.{{Cite journal |last1=Harrison |first1=R. G. |last2=Aplin |first2=K. L. |last3=Leblanc |first3=F. |last4=Yair |first4=Y. |date=June 1, 2008 |title=Planetary Atmospheric Electricity |url=https://doi.org/10.1007/s11214-008-9419-z |journal=Space Science Reviews |language=en |volume=137 |issue=1 |pages=5–10 |doi=10.1007/s11214-008-9419-z |bibcode=2008SSRv..137....5H |s2cid=122675522 |issn=1572-9672}} Lightning on Jupiter is far more energetic than on Earth, despite seeming to be generated via the same mechanism. Recently, a new type of lightning was detected on Jupiter, thought to originate from "mushballs" including ammonia.{{Cite journal |last1=Becker |first1=Heidi N. |last2=Alexander |first2=James W. |last3=Atreya |first3=Sushil K. |last4=Bolton |first4=Scott J. |last5=Brennan |first5=Martin J. |last6=Brown |first6=Shannon T. |last7=Guillaume |first7=Alexandre |last8=Guillot |first8=Tristan |last9=Ingersoll |first9=Andrew P. |last10=Levin |first10=Steven M. |last11=Lunine |first11=Jonathan I. |last12=Aglyamov |first12=Yury S. |last13=Steffes |first13=Paul G. |date=August 2020 |title=Small lightning flashes from shallow electrical storms on Jupiter |url=https://www.nature.com/articles/s41586-020-2532-1 |journal=Nature |language=en |volume=584 |issue=7819 |pages=55–58 |doi=10.1038/s41586-020-2532-1 |pmid=32760043 |bibcode=2020Natur.584...55B |s2cid=220980694 |issn=1476-4687}} On Saturn lightning, initially referred to as "Saturn Electrostatic Discharge", was discovered by the Voyager 1 mission.

Lightning on Venus has been a controversial subject after decades of study. During the Soviet Venera and U.S. Pioneer missions of the 1970s and 1980s, signals suggesting lightning may be present in the upper atmosphere were detected.{{cite journal|url=http://www-ssc.igpp.ucla.edu/~strange/JATP_paper/JATP_title.html|title=Plasma Wave Evidence for Lightning on Venus|access-date=September 24, 2007|journal=Journal of Atmospheric and Terrestrial Physics|volume=57|pages=537–556|date=1995|author=Strangeway, Robert J.|bibcode=1995JATP...57..537S|doi=10.1016/0021-9169(94)00080-8|issue=5|url-status=dead|archive-url=https://web.archive.org/web/20071012160656/http://www-ssc.igpp.ucla.edu/~strange/JATP_paper/JATP_title.html|archive-date=October 12, 2007}} The short Cassini–Huygens mission fly-by of Venus in 1999 detected no signs of lightning, but radio pulses recorded by the spacecraft Venus Express (which began orbiting Venus in April 2006) may originate from lightning on Venus.{{Cite journal |last=Lorenz |first=Ralph D. |date=June 20, 2018 |title=Lightning detection on Venus: a critical review |journal=Progress in Earth and Planetary Science |volume=5 |issue=1 |pages=34 |doi=10.1186/s40645-018-0181-x |bibcode=2018PEPS....5...34L |s2cid=49563740 |issn=2197-4284|doi-access=free }}

A lightning strike can unleash a variety of effects, some temporary, including very brief emission of light, sound and electromagnetic radiation, and some long-lasting, such as death, damage, and atmospheric and environmental changes.

{{Main|Lightning strike}}

The immense amount of energy transferred in a lightning strike can have potentially devastating effect in a multitude of areas.

File: Explosionsartiger Dampfdruck zwischen Stamm und Rinde vom Blitzeinschlag sprengte Birkenrinde weg.jpg

File:Black walnut lightning strike.jpg tree in Oklahoma]]

Objects struck by lightning experience heat and magnetic forces of great magnitude. Consequently:

• The heat created by lightning currents travelling through a tree may vaporize its sap, causing a steam explosion that rips off bark or even bursts the trunk.
• Similarly water in a fractured rock may be rapidly heated such that it splits further apart.{{Cite web |title=Foss, Kanina, New evidence on lightning strikes University of the Witwatersrand, Johannesburg, Press release, 15 October 2013 |url=http://www.wits.ac.za/newsroom/newsitems/201310/21737/news_item_21737.html |url-status=dead |archive-url=https://web.archive.org/web/20151005162551/http://www.wits.ac.za/newsroom/newsitems/201310/21737/news_item_21737.html |archive-date=October 5, 2015}}{{Cite journal |last1=Knight |first1=Jasper |last2=Grab |first2=Stefan W. |year=2014 |title=Lightning as a geomorphic agent on mountain summits: Evidence from southern Africa |journal=Geomorphology |volume=204 |pages=61–70 |bibcode=2014Geomo.204...61K |doi=10.1016/j.geomorph.2013.07.029}}
• A struck tree may catch fire, or a forest fire may be started. See also fire lightning below.
• As lightning travels through sandy soil, the soil surrounding the plasma channel may melt, forming tubular structures called fulgurites.

Buildings or tall structures hit by lightning may be damaged as the lightning seeks unimpeded paths to the ground. By safely conducting a lightning strike to the ground, a lightning protection system, usually incorporating at least one lightning rod, can greatly reduce the probability of severe property damage. Surge protection devices (SPDs) can additionally or alternatively be used to help protect electrical installations from lightning induced electrical surges that risk damaging or destroying electrical equipment or starting a fire. Electrical fires obviously threaten not only structures but all assets, personal possessions, and living beings (people, pets and livestock) within. What, if any, protection system a building or structure requires is determined through a risk assessment. Threats to structures come not only from direct strikes to the structure itself, but also from direct or indirect strikes to connected electrically conductive services (electrical power lines; communication lines; water/gas pipes), or even to the surrounding area from which a surge may reach a service connection as it spreads out into the ground.

Aircraft are highly susceptible to being struck due to their metallic fuselages, but lightning strikes are generally not dangerous to them.{{Cite web|title=What happens when lightning strikes an airplane?|url=https://www.scientificamerican.com/article/what-happens-when-lightni/|date=August 14, 2006|website=Scientific American}} Due to the conductive properties of aluminium alloy, the fuselage acts as a Faraday cage. Present day aircraft are built to be safe from a lightning strike and passengers will generally not even know that it has happened. However, there have been suspicions that lightning strikes can ignite fuel vapor and cause explosion,{{citation needed|date=December 2024}} and nearby lightning can momentarily blind the pilot and cause permanent errors in magnetic compasses.{{cite web |title=FAA-H-8083-28A, Aviation Weather Handbook |url=https://www.faa.gov/regulationspolicies/handbooksmanuals/aviation/faa-h-8083-28a-aviation-weather-handbook |publisher=Federal Aviation Administration |access-date=24 December 2024 |page=22-7}}

Although 90 percent of people struck by lightning survive,{{cite web|url=http://www.outsideonline.com/outdoor-adventure/nature/The-Body-Electric.html|title=Lightning-Strike Survivors Tell Their Stories|last1=Jabr|first1=Ferris|date=September 22, 2014|work=Outside|access-date=September 28, 2014|url-status=dead|archive-url=https://web.archive.org/web/20140928220906/http://www.outsideonline.com/outdoor-adventure/nature/The-Body-Electric.html|archive-date=September 28, 2014}} humans and other animals struck by lightning may suffer severe injury due to internal organ and nervous system damage.

{{main|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 usually multiple-stroke characteristic of the lightning strike.{{cite web |url=https://www.nationalgeographic.com/environment/article/lightning |work=National Geographic |title=Lightning|date=October 9, 2009 }} Thunder is heard as a rolling, gradually dissipating rumble because the sound from different portions of a long stroke arrives at slightly different times.Uman (1986) pp. 103–110

Lightning at a sufficient distance may be seen and not heard; there is data that a lightning storm can be seen at over {{convert|100|mi|km|order=flip|abbr=in}} whereas the thunder travels about {{convert|20|mi|km|order=flip|abbr=in}}. Anecdotally, there are many examples of people describing a 'storm directly overhead' or 'all-around' and yet 'no thunder'. Since thunderclouds can be up to {{convert|20|km|mi|abbr=in}} high,{{Cite web|url=https://factfile.org/10-facts-about-cumulonimbus-clouds|title = 10 Facts about Cumulonimbus Clouds|date = May 17, 2016}} lightning occurring high up in the cloud may appear close but is actually too far away to produce noticeable thunder.

Light travels at about {{cvt|300,000,000|m/s}}, while sound only travels through air at about {{cvt|343|m/s}}. An observer can approximate the distance to the strike by timing the interval between the visible lightning and the audible thunder it generates. A lightning flash preceding its thunder by one second would be approximately {{convert|343|m|mi|abbr=in}} away; thus a delay of three seconds would indicate a distance of about {{convert|1|km|mi|abbr=in}}; while a flash preceding thunder by five seconds would indicate a distance of roughly {{convert|1|mi|km|abbr=out}}. Consequently, a lightning strike observed at a very close distance will be accompanied by a sudden clap of thunder, with almost no perceptible time lapse, possibly accompanied by the smell of ozone (O₃).

Electromagnetic waves are emitted in a variety of wavelengths, most obviously that of visible light – the big bright flash. This emitted radiation results partly from black-body radiation due to the temperature increase caused by electrical resistance of the air,{{cite journal |last1=Kieu |first1=N. |last2=Gordillo-Vázquez |first2=F. J. |last3=Passas |first3=M. |last4=Sánchez |first4=J. |last5=Pérez-Invernón |first5=F. J. |last6=Luque |first6=A. |last7=Montanyá |first7=J. |last8=Christian |first8=H. |title=Submicrosecond Spectroscopy of Lightning-Like Discharges: Exploring New Time Regimes |journal=Geophysical Research Letters |date=16 August 2020 |volume=47 |issue=15 |pages=e2020GL088755 |doi=10.1029/2020GL088755|pmid=32999518 |pmc=7507749 |bibcode=2020GeoRL..4788755K |hdl=10261/218540 |hdl-access=free }} and partly for other reasons that are still being actively researched.{{cite web |title=Explaining high-frequency radio waves generated during lightning strikes |url=https://ww2.aip.org/scilights/explaining-high-frequency-radio-waves-generated-during-lightning-strikes |website=AIP |access-date=3 February 2025 |language=en |date=2 September 2022}}

{{further|Radio atmospheric signal|label1=Radio atmospheric|Whistler (radio)|label2=Whistler|Schumann resonances}}

Lightning discharges generate radio-frequency electromagnetic waves which can be received thousands of kilometers from their source. The discharge by itself is relatively simple short-lived dipole source that creates a single electromagnetic pulse with a duration of about 1 ms and a wide spectral density.

In the absence in the nearby environment of materials with magnetic or electrical interaction properties, at a large distances in a far field zone, the electromagnetic wave will be proportional to the second derivation of the discharge current.{{cite book|last1=Landau|first1=Lev D|author1-link=Lev Landau|last2=Lifshitz|first2=Evgeny M|author2-link=Evgeny Lifshitz|title=The Classical Theory of Fields|volume=2|edition=4th|publisher=Butterworth-Heinemann|date=1975|isbn=978-0-7506-2768-9}} This is what happens with high-altitude discharges or discharges over areas of a dry land.

{{multiple image

| align=center

| total_width=800

| image_gap=12

| image1=

| caption1=A single unaffected discharge over a dry land.

| image2=

| caption2=A discharge above conductive ground that induced local Eddy currents.

| image3=

| caption3=A discharge above oceanic waters triggered resonance oscillations.

| footer=Electromagnetic signals in a 10 Hz to 4 kHz frequency range produced by three different lightning discharges occurring thousands of kilometers away from the same registering station.{{cite web |url=https://hmicom.com/Archive/X3PE2ANC|title=Electromagnetic field records taken August 2016 near Stewart BC, Canada.|last=Issinski|first=A.|date=2016-08-28}} The lightning's local environment altered the shape of the received far field signal.

}}

In other cases, the surrounding environment will change the shape of the source signal by absorbing some of its spectrum and converting it into a heat or re-transmitting it back as modified electromagnetic waves.{{cite book|last1=Landau|first1=Lev D|author1-link=Lev Landau|last2=Lifshitz|first2=Evgeny M|author2-link=Evgeny Lifshitz|last3=Pitaevskii|first3=Lev P|author3-link=Lev Pitaevskii|title=Electrodynamics of Continuous Media|volume=8|edition=2nd|publisher=Butterworth-Heinemann|date=1984|isbn=978-0-7506-2634-7}}

{{further|Terrestrial gamma-ray flash}}

The production of X-rays by a bolt of lightning was predicted as early as 1925 by C.T.R. Wilson,{{cite journal | last1 = Wilson | first1 = C.T.R. | date = 1925 | title = The acceleration of beta-particles in strong electric fields such as those of thunderclouds | journal = Proceedings of the Cambridge Philosophical Society | volume = 22 |pages = 534–538 |bibcode = 1925PCPS...22..534W |doi = 10.1017/S0305004100003236 | issue = 4 | s2cid = 121202128 }} but no evidence was found until 2001/2002,{{Cite journal | last1 = Moore | first1 = C. B. | last2 = Eack | first2 = K. B. | last3 = Aulich | first3 = G. D. | last4 = Rison | first4 = W. | title = Energetic radiation associated with lightning stepped-leaders | doi = 10.1029/2001GL013140 | journal = Geophysical Research Letters | volume = 28 | issue = 11 | page = 2141 | year = 2001 |bibcode = 2001GeoRL..28.2141M | doi-access = free }}{{Cite journal | last1 = Dwyer | first1 = J. R. | last2 = Uman | first2 = M. A. | last3 = Rassoul | first3 = H. K. | last4 = Al-Dayeh | first4 = M. | last5 = Caraway | first5 = L. | last6 = Jerauld | first6 = J. | last7 = Rakov | first7 = V. A. | last8 = Jordan | first8 = D. M. | last9 = Rambo | first9 = K. J. | last10 = Corbin | first10 = V. | last11 = Wright | first11 = B. | title = Energetic Radiation Produced During Rocket-Triggered Lightning | doi = 10.1126/science.1078940 | journal = Science | volume = 299 | issue = 5607 | pages = 694–697 | year = 2003 | pmid = 12560549 | url = http://www.lightning.ece.ufl.edu/PDF/Dwyer_et_al_2003.pdf | bibcode = 2003Sci...299..694D | s2cid = 31926167 | url-status = dead | archive-url = https://web.archive.org/web/20160304220240/http://www.lightning.ece.ufl.edu/PDF/Dwyer_et_al_2003.pdf | archive-date = March 4, 2016 | df = mdy-all | access-date = August 28, 2015 }}Newitz, A. (September 2007) "Educated Destruction 101", Popular Science, p. 61. when researchers at the New Mexico Institute of Mining and Technology detected X-ray emissions from an induced lightning strike along a grounded wire trailed behind a rocket shot into a storm cloud. In the same year, University of Florida and Florida Tech researchers used an array of electric field and X-ray detectors at a lightning research facility in North Florida to confirm that natural lightning makes X-rays in large quantities during the propagation of stepped leaders. The cause of the X-ray emissions is still a matter for research, as the temperature of lightning is too low to account for the X-rays observed.[http://www.physorg.com/news135351802.html Scientists close in on source of X-rays in lightning] {{webarchive|url=https://web.archive.org/web/20080905120610/http://www.physorg.com/news135351802.html |date=September 5, 2008 }}, Physorg.com, July 15, 2008. Retrieved July 2008.{{cite web | url=http://www.sci-news.com/othersciences/geophysics/article00996.html | title=Scientists Explain Invisible 'Dark Lightning' | website=Sci-News.com | date=April 11, 2013 | access-date=July 9, 2013 | author=Prostak, Sergio | url-status=dead | archive-url=https://web.archive.org/web/20130620185324/http://www.sci-news.com/othersciences/geophysics/article00996.html | archive-date=June 20, 2013 | df=mdy-all }}

A number of observations by space-based telescopes have revealed even higher energy gamma ray emissions, the so-called terrestrial gamma-ray flashes (TGFs). These observations pose a challenge to current theories of lightning, especially with the recent discovery of the clear signatures of antimatter produced in lightning.{{Cite web|title=Signature of antimatter detected in lightning|url=https://www.sciencenews.org/article/signature-antimatter-detected-lightning|website=Science News|last=Cowen|first=Ron|date=November 6, 2009|access-date=July 28, 2023|archive-date=July 28, 2023|archive-url=https://web.archive.org/web/20230728171126/https://www.sciencenews.org/article/signature-antimatter-detected-lightning|url-status=live}} Recent research has shown that secondary species, produced by these TGFs, such as electrons, positrons, neutrons or protons, can gain energies of up to several tens of MeV.{{cite journal|last1=Köhn |first1=C. |last2=Ebert |first2=U.|author2-link= Ute Ebert |title=Calculation of beams of positrons, neutrons and protons associated with terrestrial gamma-ray flashes |journal=J. Geophys. Res. Atmos. |date=2015 |volume=23 |issue=4 |doi=10.1002/2014JD022229 |pages=1620–1635|bibcode=2015JGRD..120.1620K |url=https://ir.cwi.nl/pub/23845 |doi-access=free }}{{cite journal|last1=Köhn |first1=C. |last2=Diniz |first2=G. |last3=Harakeh |first3=Muhsin |title=Production mechanisms of leptons, photons, and hadrons and their possible feedback close to lightning leaders |journal=J. Geophys. Res. Atmos. |date=2017 |volume=122 |issue=2 |pages=1365–1383 |doi=10.1002/2016JD025445|pmid=28357174 |pmc=5349290 |bibcode=2017JGRD..122.1365K }}

More permanent or longer-lasting environmental changes include the following.

The very high temperatures generated by lightning lead to significant local increases in ozone and oxides of nitrogen. Each lightning flash in temperate and sub-tropical areas produces 7 kg of {{NOx}} on average.{{cite magazine|url=https://www.sciencedaily.com/releases/2009/10/091030100022.htm|title=Lightning's 'NOx-ious' Impact On Pollution, Climate|magazine= Science News|access-date=August 4, 2018}} In the troposphere the effect of lightning can increase {{NOx}} by 90% and ozone by 30%.{{cite web|url=https://www.nasa.gov/centers/goddard/news/topstory/2003/0312pollution.html|publisher=NASA|title=Surprise! Lightning has big effect on atmospheric chemistry|access-date=August 4, 2018|archive-date=March 9, 2019|archive-url=https://web.archive.org/web/20190309075516/https://www.nasa.gov/centers/goddard/news/topstory/2003/0312pollution.html|url-status=dead}}

Lightning serves an important role in the nitrogen cycle by oxidizing diatomic nitrogen in the air into nitrates which are deposited by rain and can fertilize the growth of plants and other organisms.{{cite journal | last1 = Bond | first1 = D.W. | last2 = Steiger | first2 = S. | last3 = Zhang | first3 = R. | last4 = Tie | first4 = X. | last5 = Orville | first5 = R.E. | year = 2002 | title = The importance of NOx production by lightning in the tropics | journal = Atmospheric Environment | volume = 36 | issue = 9| pages = 1509–1519 | doi=10.1016/s1352-2310(01)00553-2| bibcode = 2002AtmEn..36.1509B }}Pickering, K.E., Bucsela, E., Allen, D, Cummings, K., Li, Y., MacGorman, D., Bruning, E. 2014. Estimates of Lightning NOx Production Per Flash from OMI NO2 and Lightning Observations. XV International Conference on Atmospheric Electricity, 15–20, June 2014.

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{{cite journal|title=The Re-magnetization of a Surface Outcrop by Lightning Currents|doi=10.1111/j.1365-246X.1961.tb02963.x|date=1961|last1=Graham|first1=K.W.T.|journal=Geophysical Journal International|volume=6|issue=1|page=85|bibcode = 1961GeoJ....6...85G |doi-access=free}}Cox A. (1961). [http://pubs.usgs.gov/bul/1083e/report.pdf Anomalous Remanent Magnetization of Basalt] {{webarchive|url=https://web.archive.org/web/20130529011301/http://pubs.usgs.gov/bul/1083e/report.pdf |date=May 29, 2013 }}. U.S. Geological Survey Bulletin 1038-E, pp. 131–160. but sometimes vertically, where faults, ore bodies, or ground water offers a less resistive path.Bevan B. (1995). [https://www.researchgate.net/profile/Bruce-Bevan/publication/318826400_Magnetic_surveys_and_lightning/links/59807da84585156238facc4d/Magnetic-surveys-and-lightning.pdf "Magnetic Surveys and Lightning"]. Near Surface Views (newsletter of the Near Surface Geophysics section of the Society of Exploration Geophysics). October 1995, pp. 7–8. One theory suggests that lodestones, natural magnets encountered in ancient times, were created in this manner.{{cite journal |doi=10.1029/1999GL900496 |first=Peter |last=Wasilewski |author2=Günther Kletetschka |title=Lodestone: Nature's only permanent magnet – What it is and how it gets charged |url=http://lep694.gsfc.nasa.gov/gunther/gunther/Wasilewski1999.pdf |archive-url=https://web.archive.org/web/20061003193325/http://lep694.gsfc.nasa.gov/gunther/gunther/Wasilewski1999.pdf |archive-date=October 3, 2006 |journal=Geophysical Research Letters |volume=26 |issue=15 |pages=2275–78 |date=1999 |access-date=July 13, 2009| url-status=dead |bibcode = 1999GeoRL..26.2275W | s2cid=128699936}}

Lightning-induced magnetic anomalies can be mapped in the ground,{{Cite journal |last1=Sakai |first1=H. S. |last2=Sunada |first2=S. |last3=Sakurano |first3=H. |date=1998 |title=Study of Lightning Current by Remanent Magnetization |journal=Electrical Engineering in Japan |volume=123 |issue=4 |pages=41–47 |doi=10.1002/(SICI)1520-6416(199806)123:4<41::AID-EEJ6>3.0.CO;2-O}}[http://www.archaeophysics.com/pubs/LIRM.html Archaeo-Physics, LLC | Lightning-induced magnetic anomalies on archaeological sites] {{webarchive|url=https://web.archive.org/web/20071012080847/http://www.archaeophysics.com/pubs/LIRM.html |date=October 12, 2007 }}. Archaeophysics.com. Retrieved on June 23, 2012. and analysis of magnetized materials can confirm lightning was the source of the magnetization{{Cite journal |last=Maki |first=David |date=2005 |title=Lightning strikes and prehistoric ovens: Determining the source of magnetic anomalies using techniques of environmental magnetism |journal=Geoarchaeology |volume=20 |issue=5 |pages=449–459 |doi=10.1002/gea.20059 |bibcode=2005Gearc..20..449M |url=http://www.archaeophysics.com/pubs/lightning-oven.pdf |url-status=dead |archive-url=https://web.archive.org/web/20130515025335/http://www.archaeophysics.com/pubs/lightning-oven.pdf |archive-date=May 15, 2013 |citeseerx=10.1.1.536.5980 |s2cid=52383921 |access-date=November 1, 2017 }} and provide an estimate of the peak current of the lightning discharge.{{Cite journal |last1=Verrier |first1=V. |last2=Rochette |first2=P. |date=2002 |title=Estimating Peak Currents at Ground Lightning Impacts Using Remanent Magnetization |journal=Geophysical Research Letters |volume=29 |issue=18 |page=1867 |doi=10.1029/2002GL015207|bibcode = 2002GeoRL..29.1867V |s2cid=128577288 |doi-access=free }}

Research at the University of Innsbruck has calculated that magnetic fields generated by plasma may induce hallucinations in subjects located within {{cvt|200|m}} of a severe lightning storm, like what happened in Transcranial magnetic stimulation (TMS).{{cite web | url=https://www.technologyreview.com/s/418887/magnetically-induced-hallucinations-explain-ball-lightning-say-physicists/ |title = Magnetically Induced Hallucinations Explain Ball Lightning, Say Physicists}}

{{main|Lightning detection}}

File:Museu Romàntic Can Papiol. Maig 2014 05.JPG

The earliest detector invented to warn of the approach of a thunderstorm was the lightning bell. Benjamin Franklin installed one such device in his house.The Franklin Institute. [http://sln.fi.edu/franklin/bells.html Ben Franklin's Lightning Bells] {{webarchive|url=https://web.archive.org/web/20081212052405/http://sln.fi.edu/franklin/bells.html |date=December 12, 2008 }}. Retrieved December 14, 2008.Rimstar.org [https://www.youtube.com/watch?v=fEqudsyIWzk Video demonstration of how Franklin's Bell worked] {{webarchive|url=https://web.archive.org/web/20160806121106/https://www.youtube.com/watch?v=fEqudsyIWzk |date=August 6, 2016 }} The detector was based on an electrostatic device called the 'electric chimes' invented by Andrew Gordon in 1742.

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

|title = Lightning Detection Systems

|url = http://www.nwstc.noaa.gov/METEOR/Lightning/detection.htm

|access-date = July 27, 2007

|url-status = dead

|archive-url = https://web.archive.org/web/20080917190959/http://www.nwstc.noaa.gov/METEOR/Lightning/detection.htm

|archive-date = September 17, 2008

|df = mdy-all

}} NOAA page on how the U.S. national lightning detection system operates{{cite web | title = Vaisala Thunderstorm Online Application Portal

| url = https://thunderstorm.vaisala.com/tux/jsp/explorer/explorer.jsp

| archive-url = https://web.archive.org/web/20070928033058/https://thunderstorm.vaisala.com/tux/jsp/explorer/explorer.jsp

| archive-date = September 28, 2007

| access-date = July 27, 2007 }} Real-time map of lightning discharges in U.S.

In addition, Blitzortung (a private global detection system that consists of over 500 detection stations owned and operated by hobbyists/volunteers) provides near real-time lightning maps at [https://archive.today/20161216132732/http://en.blitzortung.org/].

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 locating lightning strikes up to distances of 10,000 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.Volland, H. (ed) (1995) Handbook of Atmospheric Electrodynamics, CRC Press, Boca Raton, {{ISBN|0849386470}}.

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.{{cite web| url=http://thunder.msfc.nasa.gov/data/| title=NASA Dataset Information| access-date=September 11, 2007| publisher=NASA| date=2007| url-status=dead| archive-url=https://web.archive.org/web/20070915074014/http://thunder.msfc.nasa.gov/data/| archive-date=September 15, 2007| df=mdy-all}}{{cite web|url=http://thunder.msfc.nasa.gov/data/lisbrowse.html|title=NASA LIS Images|access-date=September 11, 2007|publisher=NASA|date=2007|url-status=dead|archive-url=https://web.archive.org/web/20071012171040/http://thunder.msfc.nasa.gov/data/lisbrowse.html|archive-date=October 12, 2007}}{{cite web| url=http://thunder.msfc.nasa.gov/data/otdbrowse.html| title=NASA OTD Images| access-date=September 11, 2007| publisher=NASA| date=2007| url-status=dead| archive-url=https://web.archive.org/web/20071012171045/http://thunder.msfc.nasa.gov/data/otdbrowse.html| archive-date=October 12, 2007| df=mdy-all}}

Starting in 2016, the National Oceanic and Atmospheric Administration launched Geostationary Operational Environmental Satellite–R Series (GOES-R) weather satellites outfitted with Geostationary Lightning Mapper (GLM) instruments which are near-infrared optical transient detectors that can detect the momentary changes in an optical scene, indicating the presence of lightning.{{cite web |title=GLM │ GOES-R Series |url=https://www.goes-r.gov/spacesegment/glm.html |website=www.goes-r.gov}}{{cite news |last1=Sima |first1=Richard |title=Mapping Lightning Strikes from Space |url=https://eos.org/articles/mapping-lightning-strikes-from-space |work=Eos |date=March 13, 2020}} The lightning detection data can be converted into a real-time map of lightning activity across the Western Hemisphere; this mapping technique has been implemented by the United States National Weather Service.{{cite journal |last1=Bruning |first1=Eric C. |last2=Tillier |first2=Clemens E. |last3=Edgington |first3=Samantha F. |last4=Rudlosky |first4=Scott D. |last5=Zajic |first5=Joe |last6=Gravelle |first6=Chad |last7=Foster |first7=Matt |last8=Calhoun |first8=Kristin M. |last9=Campbell |first9=P. Adrian |last10=Stano |first10=Geoffrey T. |last11=Schultz |first11=Christopher J. |last12=Meyer |first12=Tiffany C. |title=Meteorological Imagery for the Geostationary Lightning Mapper |journal=Journal of Geophysical Research: Atmospheres |date=2019 |volume=124 |issue=24 |pages=14285–14309 |doi=10.1029/2019JD030874 |bibcode=2019JGRD..12414285B |doi-access=free |hdl=2346/95772 |hdl-access=free }}

In 2022 EUMETSAT plan to launch the Lightning Imager (MTG-I LI) on board Meteosat Third Generation. This will complement NOAA's GLM. MTG-I LI will cover Europe and Africa and will include products on events, groups and flashes.{{Cite web |title=Lightning Imager |url=https://www.eumetsat.int/mtg-lightning-imager |access-date=July 27, 2022 |website=EUMETSAT |date=May 21, 2020 |archive-date=July 14, 2022 |archive-url=https://web.archive.org/web/20220714105714/https://www.eumetsat.int/mtg-lightning-imager |url-status=dead }}

• Rocket-triggered
• : Lightning can be "triggered" by launching specially designed rockets trailing spools of wire into thunderstorms. The wire unwinds as the rocket ascends, creating an elevated ground that can attract descending leaders. If a leader attaches, the wire provides a low-resistance pathway for a lightning flash to occur. The wire is vaporized by the return current flow, creating a straight lightning plasma channel in its place. This method allows for scientific research of lightning to occur under a more controlled and predictable manner.{{cite web|url=http://skydiary.com/gallery/chase2002/2002lightmovie.html|title=Triggered lightning video|access-date=September 24, 2007|publisher=Chris Kridler's Sky Diary|date=July 25, 2002|author=Kridler, Chris|work=requires QuickTime|format=video|url-status=dead|archive-url=https://web.archive.org/web/20070915074527/http://skydiary.com/gallery/chase2002/2002lightmovie.html|archive-date=September 15, 2007}} The International Center for Lightning Research and Testing (ICLRT) at Camp Blanding, Florida typically uses rocket triggered lightning in their research studies.
• 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.{{cite web | title = UNM researchers use lasers to guide lightning| publisher = Campus News, The University of New Mexico| date = January 29, 2001| url = http://panda.unm.edu/AcadAdv/lightning.html | archive-url = https://web.archive.org/web/20120709023513/http://panda.unm.edu/AcadAdv/lightning.html | archive-date = July 9, 2012 | access-date = July 28, 2007}}{{Cite journal | doi = 10.1088/1367-2630/4/1/361| title = Laser-triggered lightning discharge| journal = New Journal of Physics| volume = 4| issue = 1| page = 61| year = 2002| last1 = Khan | first1 = N. | last2 = Mariun | first2 = N. | last3 = Aris | first3 = I. | last4 = Yeak | first4 = J. |bibcode = 2002NJPh....4...61K | doi-access = free }}{{Cite journal |doi=10.1364/JOT.66.000194 |title=Laboratory tests of laser-induced lightning discharge |journal=Journal of Optical Technology |volume=66 |issue=3 |pages=194–198 |date=1999 |first1=P. |last1=Rambo |first2=J. |last2=Biegert |first3=V. |last3=Kubecek |first4=J. |last4=Schwarz |first5=A. |last5=Bernstein |first6=J.-C. |last6=Diels |first7=R. |last7=Bernstein |name-list-style=amp |first8=K. |last8=Stahlkopf |bibcode=1999JOptT..66..194R }}{{Cite journal | doi = 10.1063/1.1829165| title = Triggering and guiding of megavolt discharges by laser-induced filaments under rain conditions| journal = Applied Physics Letters| volume = 85| issue = 23| page = 5781| year = 2004| last1 = Ackermann | first1 = R.| last2 = Stelmaszczyk | first2 = K.| last3 = Rohwetter | first3 = P.| last4 = MéJean | first4 = G.| last5 = Salmon | first5 = E.| last6 = Yu | first6 = J.| last7 = Kasparian | first7 = J.| last8 = MéChain | first8 = G.| last9 = Bergmann | first9 = V.| last10 = Schaper | first10 = S.| last11 = Weise | first11 = B.| last12 = Kumm | first12 = T.| last13 = Rethmeier | first13 = K.| last14 = Kalkner | first14 = W.| last15 = WöSte | first15 = L.| last16 = Wolf | first16 = J. P.|bibcode = 2004ApPhL..85.5781A }}{{Cite journal | doi = 10.1016/0021-9169(94)00073-W| title = A possible way to trigger lightning using a laser| journal = Journal of Atmospheric and Terrestrial Physics| volume = 57| issue = 5| page = 459| year = 1995| last1 = Wang | first1 = D.| last2 = Ushio | first2 = T.| last3 = Kawasaki | first3 = Z. -I. | last4 = Matsuura | first4 = K.| last5 = Shimada | first5 = Y.| last6 = Uchida | first6 = S.| last7 = Yamanaka | first7 = C.| last8 = Izawa | first8 = Y.| last9 = Sonoi | first9 = Y.| last10 = Simokura | first10 = N.|bibcode = 1995JATP...57..459W }}
• : 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 a period too short 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.{{cite web |url=http://infoniac.com/science/terawatt-laser-beam-shot-clouds-provokes-lightning-strike.html |title=Terawatt Laser Beam Shot in the Clouds Provokes Lightning Strike |url-status=dead |archive-url=https://web.archive.org/web/20080420130439/http://infoniac.com/science/terawatt-laser-beam-shot-clouds-provokes-lightning-strike.html |archive-date=April 20, 2008 |access-date=April 17, 2008 }} News report based on: {{Cite journal | doi = 10.1364/OE.16.005757 | pmid = 18542684 | title = Electric events synchronized with laser filaments in thunderclouds | journal = Optics Express | volume = 16 | issue = 8 | pages = 5757–63 | year = 2008 | last1 = Kasparian | first1 = J. | last2 = Ackermann | first2 = R. | last3 = André | first3 = Y. B. | last4 = Méchain | first4 = G. G. | last5 = Méjean | first5 = G. | last6 = Prade | first6 = B. | last7 = Rohwetter | first7 = P. | last8 = Salmon | first8 = E. | last9 = Stelmaszczyk | first9 = K. | last10 = Yu | first10 = J. | last11 = Mysyrowicz | first11 = A. | last12 = Sauerbrey | first12 = R. | last13 = Woeste | first13 = L. | last14 = Wolf | first14 = J. P. | bibcode = 2008OExpr..16.5757K | url = https://www.osapublishing.org/oe/abstract.cfm?uri=oe-16-8-5757 | doi-access = free }} 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.{{cite web |url=http://newswise.com/articles/view/539709/ |title=Laser Triggers Electrical Activity in Thunderstorm for the First Time |work=Newswise |access-date=August 6, 2008 |url-status=dead |archive-url=https://web.archive.org/web/20081220100906/http://newswise.com/articles/view/539709/ |archive-date=December 20, 2008 }} News report based on {{Harvard citation no brackets|Kasparian|Ackermann|André|Méchain|Méjean|Prade|Rohwetter|Salmon|Stelmaszczyk|Yu|Mysyrowicz|Sauerbrey|Woeste|Wolf|2008|pp=5757–5763}}

It is difficult to accurately predict changes in lightning due to climate change because it is challenging to simulate cloud physics variables that predict lightning (such as convection and cloud ice) in climate models.{{Cite journal |last1=Clark |first1=Spencer K. |last2=Ward |first2=Daniel S. |last3=Mahowald |first3=Natalie M. |date=2017 |title=Parameterization-based uncertainty in future lightning flash density |url=https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017GL073017 |journal=Geophysical Research Letters |language=en |volume=44 |issue=6 |pages=2893–2901 |doi=10.1002/2017GL073017 |bibcode=2017GeoRL..44.2893C |issn=1944-8007}}{{Cite journal |last1=Charn |first1=Alexander B. |last2=Parishani |first2=Hossein |date=2021 |title=Predictive Proxies of Present and Future Lightning in a Superparameterized Model |url=https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2021JD035461 |journal=Journal of Geophysical Research: Atmospheres |language=en |volume=126 |issue=17 |pages=e2021JD035461 |doi=10.1029/2021JD035461 |bibcode=2021JGRD..12635461C |issn=2169-8996}}

A large share of the world's lightning occurs over Africa.{{Cite journal |last1=Albrecht |first1=Rachel I. |last2=Goodman |first2=Steven J. |last3=Buechler |first3=Dennis E. |last4=Blakeslee |first4=Richard J. |last5=Christian |first5=Hugh J. |date=2016-11-01 |title=Where Are the Lightning Hotspots on Earth? |url=https://journals.ametsoc.org/view/journals/bams/97/11/bams-d-14-00193.1.xml |journal=Bulletin of the American Meteorological Society |language=EN |volume=97 |issue=11 |pages=2051–2068 |doi=10.1175/BAMS-D-14-00193.1 |bibcode=2016BAMS...97.2051A |issn=0003-0007}} While there are regional variations in how climate change affects lightning across the continent, one study predicts a small increase in the total amount of lightning across the continent with warming. More specifically, the total number of lightning days per year is predicted to decrease, while more cloud ice and stronger convection leads to more lightning strikes occurring on days when lightning does occur.{{Cite journal |last1=Finney |first1=D. L. |last2=Marsham |first2=J. H. |last3=Wilkinson |first3=J. M. |last4=Field |first4=P. R. |last5=Blyth |first5=A. M. |last6=Jackson |first6=L. S. |last7=Kendon |first7=E. J. |last8=Tucker |first8=S. O. |last9=Stratton |first9=R. A. |date=2020 |title=African Lightning and its Relation to Rainfall and Climate Change in a Convection-Permitting Model |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020GL088163 |journal=Geophysical Research Letters |language=en |volume=47 |issue=23 |pages=e2020GL088163 |doi=10.1029/2020GL088163 |bibcode=2020GeoRL..4788163F |issn=1944-8007}}

Lightning is much less common near the North and South Poles than in other regions.{{Cite journal |last1=Kaplan |first1=Jed O. |last2=Lau |first2=Katie Hong-Kiu |date=2021-07-06 |title=The WGLC global gridded lightning climatology and time series |url=https://essd.copernicus.org/articles/13/3219/2021/ |journal=Earth System Science Data |language=English |volume=13 |issue=7 |pages=3219–3237 |doi=10.5194/essd-13-3219-2021 |doi-access=free |bibcode=2021ESSD...13.3219K |issn=1866-3508}}{{Cite journal |last1=Virts |first1=Katrina S. |last2=Wallace |first2=John M. |last3=Hutchins |first3=Michael L. |last4=Holzworth |first4=Robert H. |date=2013-09-01 |title=Highlights of a New Ground-Based, Hourly Global Lightning Climatology |url=https://journals.ametsoc.org/view/journals/bams/94/9/bams-d-12-00082.1.xml |journal=Bulletin of the American Meteorological Society |language=EN |volume=94 |issue=9 |pages=1381–1391 |doi=10.1175/BAMS-D-12-00082.1|bibcode=2013BAMS...94.1381V }} However, climate models increasingly agree that lightning in the Arctic has increased due to climate change.{{Cite journal |last1=Chen |first1=Yang |last2=Romps |first2=David M. |last3=Seeley |first3=Jacob T. |last4=Veraverbeke |first4=Sander |last5=Riley |first5=William J. |last6=Mekonnen |first6=Zelalem A. |last7=Randerson |first7=James T. |date=5 April 2021 |title=Future increases in Arctic lightning and fire risk for permafrost carbon |url=https://www.nature.com/articles/s41558-021-01011-y |journal=Nature Climate Change |language=en |volume=11 |issue=5 |pages=404–410 |doi=10.1038/s41558-021-01011-y |bibcode=2021NatCC..11..404C |hdl=1871.1/5d9d7857-98f5-4339-bb11-a05d9d321fac |issn=1758-6798}}{{Cite journal |last=Finney |first=Declan L. |date=5 April 2021 |title=Lightning threatens permafrost |url=https://www.nature.com/articles/s41558-021-01016-7 |journal=Nature Climate Change |language=en |volume=11 |issue=5 |pages=379–380 |doi=10.1038/s41558-021-01016-7 |bibcode=2021NatCC..11..379F |issn=1758-6798}} and will continue to increase in future.{{Cite web |last=Ramirez |first=Rachel |date=2022-01-05 |title=Another sign things are getting weird: Lightning around the North Pole increased dramatically in 2021 |url=https://edition.cnn.com/2022/01/05/world/lightning-increased-north-pole-arctic-2021-climate/index.html |access-date=2025-02-25 |website=CNN |language=en}}{{Cite journal |last1=Holzworth |first1=Robert H. |last2=Brundell |first2=James B. |last3=McCarthy |first3=Michael P. |last4=Jacobson |first4=Abram R. |last5=Rodger |first5=Craig J. |last6=Anderson |first6=Todd S. |date=2021 |title=Lightning in the Arctic |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020GL091366 |journal=Geophysical Research Letters |language=en |volume=48 |issue=7 |pages=e2020GL091366 |doi=10.1029/2020GL091366 |bibcode=2021GeoRL..4891366H |issn=1944-8007}} The ratio of Arctic summertime lightning strikes has increased from 2010 to 2020 compared to the total lightning strikes in the world, indicating that the region is becoming more influenced by lightning.{{Cite journal |last1=Holzworth |first1=Robert H. |last2=Brundell |first2=James B. |last3=McCarthy |first3=Michael P. |last4=Jacobson |first4=Abram R. |last5=Rodger |first5=Craig J. |last6=Anderson |first6=Todd S. |date=2021 |title=Lightning in the Arctic |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020GL091366 |journal=Geophysical Research Letters |language=en |volume=48 |issue=7 |pages=e2020GL091366 |doi=10.1029/2020GL091366 |bibcode=2021GeoRL..4891366H |issn=1944-8007}}

Lightning activity is increased by particulate emissions (a form of air pollution).{{Cite journal |last1=Bentley |first1=Mace |last2=Gerken |first2=Tobias |last3=Duan |first3=Zhuojun |last4=Bonsal |first4=Dudley |last5=Way |first5=Henry |last6=Szakal |first6=Endre |last7=Pham |first7=Mia |last8=Donaldson |first8=Hunter |last9=Griffith |first9=Lucie |date=2024-07-01 |title=Toward untangling thunderstorm-aerosol relationships: An observational study of regions centered on Washington, DC and Kansas City, MO |url=https://www.sciencedirect.com/science/article/pii/S0169809524001844 |journal=Atmospheric Research |volume=304 |pages=107402 |doi=10.1016/j.atmosres.2024.107402 |bibcode=2024AtmRe.30407402B |issn=0169-8095}}{{cite web |last=Ogasa |first=Nik |date=25 May 2021 |title=Air pollution helps wildfires create their own lightning |url=https://www.science.org/content/article/air-pollution-helps-wildfires-create-their-own-lightning |website=Science}}{{Cite web |last=Cartwright |first=Jon |date=2018-02-13 |title=Pollution boosts risk of lightning |url=https://physicsworld.com/a/pollution-boosts-risk-of-lightning/ |access-date=2025-02-25 |website=Physics World |language=en-GB}}{{cite web |last=Baranuik |first=Chris |date=15 November 2017 |title=A Bolt from the Brown: Why Pollution May Increase Lightning Strikes |url=https://www.scientificamerican.com/article/a-bolt-from-the-brown-why-pollution-may-increase-lightning-strikes/ |website=Scientific American}} However, this only occurs up to a point (aerosol optical depth = 0.3). Once this threshold is crossed, lightning is then suppressed by further increases in particulates.{{Cite journal |last1=Altaratz |first1=Orit |last2=Koren |first2=Ilan |last3=Yair |first3=Yoav |last4=Price |first4=Colin |date=2010 |title=Lightning response to smoke from Amazonian fires |url=https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2010GL042679 |journal=Geophysical Research Letters |language=en |volume=37 |issue=7 |doi=10.1029/2010GL042679 |bibcode=2010GeoRL..37.7801A |issn=1944-8007}}{{Cite journal |last1=Sun |first1=Mengyu |last2=Qie |first2=Xiushu |last3=Mansell |first3=Edward R. |last4=Liu |first4=Dongxia |last5=Yair |first5=Yoav |last6=Fierro |first6=Alexandre O. |last7=Yuan |first7=Shanfeng |last8=Lu |first8=Jingyu |date=2023 |title=Aerosol Impacts on Storm Electrification and Lightning Discharges Under Different Thermodynamic Environments |url=https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2022JD037450 |journal=Journal of Geophysical Research: Atmospheres |language=en |volume=128 |issue=8 |pages=e2022JD037450 |doi=10.1029/2022JD037450 |bibcode=2023JGRD..12837450S |issn=2169-8996}}

When lightning occurs, it generates rapid heating and cooling that causes gases that cause nitrogen and oxygen molecules in the atmosphere to break apart. This process leads to the formation of nitrogen oxides (NOₓ), which can subsequently result in the production of ozone, a greenhouse gas when occurring in the troposphere.{{Cite web |title=Frequently Asked Questions (FAQs) - U.S. Energy Information Administration (EIA) |url=https://www.eia.gov/tools/faqs/faq.php?id=84&t=11#:~:text=Ozone%20is%20technically%20a%20greenhouse,under%20the%20Clean%20Air%20Act. |archive-url=http://web.archive.org/web/20250222124734/https://www.eia.gov/tools/faqs/faq.php?id=84&t=11 |archive-date=2025-02-22 |access-date=2025-02-25 |website=www.eia.gov}} However, lightning NOx also leads to increased amounts of hydroxyl (OH) and hydroperoxyl (HO₂) radicals. These reactive molecules initiate chemical reactions that break down greenhouse gases like methane, effectively cleaning the atmosphere.{{Cite journal |last1=Brune |first1=W. H. |last2=McFarland |first2=P. J. |last3=Bruning |first3=E. |last4=Waugh |first4=S. |last5=MacGorman |first5=D. |last6=Miller |first6=D. O. |last7=Jenkins |first7=J. M. |last8=Ren |first8=X. |last9=Mao |first9=J. |last10=Peischl |first10=J. |date=2021-05-14 |title=Extreme oxidant amounts produced by lightning in storm clouds |url=https://www.science.org/doi/10.1126/science.abg0492 |journal=Science |volume=372 |issue=6543 |pages=711–715 |doi=10.1126/science.abg0492|pmid=33927054 |bibcode=2021Sci...372..711B }}{{Cite journal |last1=Jenkins |first1=Jena M. |last2=Brune |first2=William H. |last3=Miller |first3=David O. |date=2021 |title=Electrical Discharges Produce Prodigious Amounts of Hydroxyl and Hydroperoxyl Radicals |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2021JD034557 |journal=Journal of Geophysical Research: Atmospheres |language=en |volume=126 |issue=9 |pages=e2021JD034557 |doi=10.1029/2021JD034557 |bibcode=2021JGRD..12634557J |issn=2169-8996}}

As lightning is influenced by climate change, there is a corresponding change to the lightning’s influence on climate. These changes can lead to further climate change, thus creating a climate change feedback.{{Cite web |last1=Harris |first1=Nancy |last2=Munroe |first2=Thailynn |last3=Levin |first3=Kelly |date=16 September 2020 |title=6 Graphics Explain the Climate Feedback Loop Fueling US Fires |url=https://www.wri.org/insights/6-graphics-explain-climate-feedback-loop-fueling-us-fires |website=World Resources Institute}}

Lightning leads to the production of tropospheric ozone and destruction of methane, both greenhouse gases and air pollutants. Therefore, the net impact of lightning on climate depends on the balance between this warming and cooling effect of the gases' effects on atmospheric chemistry. Predictions of this feedback can vary, resulting in either no change (net zero feedback), or a warming effect (positive feedback), depending on the method used to predict lightning.{{Cite journal |last1=Finney |first1=Declan L. |last2=Doherty |first2=Ruth M. |last3=Wild |first3=Oliver |last4=Stevenson |first4=David S. |last5=MacKenzie |first5=Ian A. |last6=Blyth |first6=Alan M. |date=12 February 2018 |title=A projected decrease in lightning under climate change |url=https://www.nature.com/articles/s41558-018-0072-6 |journal=Nature Climate Change |language=en |volume=8 |issue=3 |pages=210–213 |doi=10.1038/s41558-018-0072-6 |bibcode=2018NatCC...8..210F |issn=1758-6798}}

Lightning is the major natural cause of wildfire,{{Cite journal |last1=Song |first1=Yang |last2=Xu |first2=Cangsu |last3=Li |first3=Xiaolu |last4=Oppong |first4=Francis |date=2 March 2024 |title=Lightning-Induced Wildfires: An Overview |journal=Fire |language=en |volume=7 |issue=3 |pages=79 |doi=10.3390/fire7030079 |doi-access=free |bibcode=2024Fire....7...79S |issn=2571-6255}} estimated to cause 10% of forest fires worldwide.{{Cite journal |last1=Malamud |first1=Bruce D. |last2=Millington |first2=James D. A. |last3=Perry |first3=George L. W. |date=2005-03-21 |title=Characterizing wildfire regimes in the United States |journal=Proceedings of the National Academy of Sciences |volume=102 |issue=13 |pages=4694–4699 |doi=10.1073/pnas.0500880102 |doi-access=free |pmid=15781868 |pmc=555719 |bibcode=2005PNAS..102.4694M |issn=0027-8424}} Wildfire can contribute to climate change.{{cite web |url=https://www.epa.gov/climate-indicators/climate-change-indicators-wildfires |title=Climate Change Indicators: Wildfires, US EPA |date=July 2016 |accessdate=July 6, 2023}} Because wildfires emit greenhouse gases, and also affect vegetation cover (which affects how much sunlight is reflected), a lightning wildfire feedback is possible. Multiple studies suggest there could be an increase in Boreal and Arctic lightning-ignited fires in response to climate change.{{Cite journal |last1=Janssen |first1=Thomas A. J. |last2=Jones |first2=Matthew W. |last3=Finney |first3=Declan |last4=van der Werf |first4=Guido R. |last5=van Wees |first5=Dave |last6=Xu |first6=Wenxuan |last7=Veraverbeke |first7=Sander |date=9 November 2023 |title=Extratropical forests increasingly at risk due to lightning fires |url=https://www.nature.com/articles/s41561-023-01322-z |journal=Nature Geoscience |language=en |volume=16 |issue=12 |pages=1136–1144 |doi=10.1038/s41561-023-01322-z |bibcode=2023NatGe..16.1136J |issn=1752-0908}} There is evidence that arctic lightning wildfire feedback may also influence vegetation and permafrost cover. The impact of lightning on fires in the tropics remains uncertain.

The first known photograph of lightning is from 1847, by Thomas Martin Easterly.{{Cite web |url=https://hyperallergic.com/301157/the-first-photographs-of-lightning-crackle-with-electric-chaos/ |title=The First Photographs of Lightning Crackle with Electric Chaos |date=May 25, 2016 |website=Hyperallergic |access-date=May 12, 2019}} The first surviving photograph is from 1882, by William Nicholson Jennings.{{Cite web |title=These are the World's First Photos of Lightning |url=https://petapixel.com/2020/08/05/these-are-the-worlds-first-photos-of-lightning/|date=August 5, 2020|website=PetaPixel}}

{{further|Lightning in religion}}

File:Mikalojus Konstantinas Ciurlionis - LIGHTNING - 1909.jpg (1909)]]

In many cultures, lightning has been viewed as a sign or part of a deity or a deity in and of itself. These include the Greek god Zeus, the Aztec god Tlaloc, the Mayan God K, Slavic mythology's Perun, the Baltic Pērkons/Perkūnas, Thor in Norse mythology, Ukko in Finnish mythology, the Hindu god Indra, the Yoruba god Sango, Illapa in Inca mythology and the Shinto god Raijin.{{cite book|pages=1909–1918|doi=10.1109/ICLP.2014.6973441|chapter=Lightning; Gods and sciences|year=2014|last1=Gomes|first1=Chandima|last2=Gomes|first2=Ashen|title=2014 International Conference on Lightning Protection (ICLP)|isbn=978-1-4799-3544-4|s2cid=21598095}} The ancient Etruscans produced guides to divining the future based on the omens supposedly displayed by thunder or lightning.{{citation |last=Turfa |first=Jean MacIntosh |title=Divining the Etruscan World: The Brontoscopic Calendar and Religious Practice |location=Cambridge |publisher=Cambridge University Press |date=2012 }}.{{citation |last=Pallottino |first=Massimo |author-link=Massimo Pallottino |translator=Cremina, J. |editor-last=Ridgway |editor-first=David |title=The Etruscans |location=Bloomington |publisher=Indiana University Press |year=1975 |isbn=0-253-32080-1 |url=https://archive.org/details/etruscans0000pall |page=154 |display-editors=0 }}. Such use of thunder and lightning in divination is also known as ceraunoscopy,{{cite web|url=http://wordinfo.info/unit/418 |title=cerauno-, kerauno- + (Greek: thunderbolt, thunder, lightning) |work=WordInfo.com|accessdate=June 11, 2010}} a kind of aeromancy. In the traditional religion of the African Bantu tribes, lightning is a sign of the ire of the gods. Scriptures in Judaism, Islam and Christianity also ascribe supernatural importance to lightning.

Although sometimes used figuratively, the idea that lightning never strikes the same place twice is a common myth. In fact, lightning can, and often does, strike the same place more than once. Lightning in a thunderstorm is more likely to strike objects and spots that are more prominent or conductive. For instance, lightning strikes the Empire State Building in New York City on average 23 times per year.{{cite web |url=https://www.weather.gov/safety/lightning-myths |title=Lightning Myths |publisher=National Weather Service |access-date=August 9, 2023}}

{{cite web|url=http://www.sti.nasa.gov/tto/Spinoff2005/ps_3.html|title=Lightning Often Strikes Twice|publisher=Office of the Chief Technologist, NASA |work=Spinoff|date=March 25, 2010|access-date=June 23, 2010|archive-url=https://web.archive.org/web/20120325015918/http://www.sti.nasa.gov/tto/Spinoff2005/ps_3.html|archive-date=March 25, 2012|url-status=dead}}{{cite web |url=https://www.theweathernetwork.com/ca/news/article/can-lightning-strike-the-same-place-twice |title=Can lightning strike the same place twice? |work=The Weather Network |last=Simpson |first=Tristan |date=April 29, 2022 |access-date=August 9, 2023}}

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".

File:Yli-ii.vaakuna.svg municipality]]

The bolt of lightning in heraldry is called a thunderbolt. This symbol usually represents power and speed.

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.[http://mauryk2.com/2010/11/06/john-kasper-the-national-states-rights-party-and-the-demise-of-the-old-south/ 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)] {{webarchive|url=https://web.archive.org/web/20130203185623/http://mauryk2.com/2010/11/06/john-kasper-the-national-states-rights-party-and-the-demise-of-the-old-south/ |date=February 3, 2013}}. Mauryk2.com (November 6, 2010). Retrieved on April 9, 2013. The Schutzstaffel, the paramilitary wing of the Nazi Party, used the Sig rune in their logo which symbolizes lightning. The German word Blitzkrieg, which means "lightning war", was a major offensive strategy of the German army during World War II.

The lightning bolt is a common insignia for military communications units. A lightning bolt is also the NATO symbol for a signal asset.

{{Portal|Environment|Weather}}

{{Div col|colwidth=20em}}

• Lightning strike
• Volcanic lightning
• Paleolightning
• Harvesting lightning energy
• Keraunography
• Keraunomedicine – medical study of lightning casualties
• Lichtenberg figure
• Lightning injury
• Lightning-prediction system
• Roy Sullivan - Sullivan is recognized by Guinness World Records as the person struck by lightning more recorded times than any other human
• St. Elmo's fire
• Upper-atmospheric lightning
• Vela satellites – satellites which could record lightning superbolts

{{div col end}}

{{Reflist|30em|refs=

• {{Cite journal |first1=David W. |last1=Koopman |name-list-style=amp |first2=T. D. |last2=Wilkerson |date=1971 |title=Channeling of an Ionizing Electrical Streamer by a Laser Beam |journal=Journal of Applied Physics |volume=42 |issue=5 |pages=1883–1886 |doi=10.1063/1.1660462|bibcode = 1971JAP....42.1883K }}
• {{Cite journal |first1=K. A. |last1=Saum |name-list-style=amp |first2=David W. |last2=Koopman |date=November 1972 |title=Discharges Guided by Laser-Induced Rarefaction Channels |journal=Physics of Fluids |volume=15 |issue=11 |pages=2077–2079 |doi=10.1063/1.1693833 |bibcode = 1972PhFl...15.2077S }}
• {{Cite journal |first=C. W. |last=Schubert |date=1977 |title=The laser lightning rod: A feasibility study |journal=Technical Report AFFDL-TR-78-60, ADA063847, [U.S.] Air Force Flight Dynamics Laboratory, Wright-Patterson AFB [Air Force Base] Ohio |url=http://oai.dtic.mil/oai/oai?verb=getRecord&metadataPrefix=html&identifier=ADA063847 |url-status=dead |archive-url=https://web.archive.org/web/20081224085244/http://oai.dtic.mil/oai/oai?verb=getRecord&metadataPrefix=html&identifier=ADA063847 |archive-date=December 24, 2008 |access-date=December 13, 2018 }}
• {{Cite book |first1=Charles W. |last1=Schubert |name-list-style=amp |first2=Jack R. |last2=Lippert |date=1979 |chapter=Investigation into triggering lightning with a pulsed laser |editor1-first=A. H. |editor1-last=Guenther |editor2-first=M. |editor2-last=Kristiansen |title=Proceedings of the 2nd IEEE International Pulse Power Conference, Lubbock, Texas, 1979 |location=Piscataway, New Jersey |publisher=IEEE |pages=132–135 |url=https://inis.iaea.org/collection/NCLCollectionStore/_Public/16/076/16076157.pdf }}
• {{cite journal|bibcode=1978affd.rept.....L|title=A laser-induced lightning concept experiment|date=1977|author=Lippert, J. R.|journal=Final Report}}
• Rakov and Uman, pp. 296–299.

}}

• {{Cite book |author1=Rakov, Vladimir A. |author2=Uman, Martin A. |title=Lightning: Physics and effects |location=Cambridge, England |publisher=Cambridge University Press |date=2003|url=https://books.google.com/books?id=NviMsvVOHJ4C&pg=PA296|isbn=978-0521583275|ref=Rakov}}
• {{cite book | author= Uman, Martin A. | title= All About Lightning | publisher= Dover Publications, Inc. | date= 1986 | pages= [https://archive.org/details/allaboutlightnin0000uman/page/103 103–110] | isbn= 978-0-486-25237-7 | author-link= Martin A. Uman | ref= Uman | url-access= registration | url= https://archive.org/details/allaboutlightnin0000uman/page/103 }}
• {{Include-NOAA|article=Understanding Lightning: Thunderstorm Electrification|url=http://www.lightningsafety.noaa.gov/science/science_electrication.htm}}

• {{cite journal |last=Anders |first=André |title=Tracking Down the Origin of Arc Plasma Science I. Early Pulsed and Oscillating Discharges| journal=IEEE Transactions on Plasma Science|date=2003|volume=31|issue=4|pages=1052–1059|doi=10.1109/TPS.2003.815476 |bibcode= 2003ITPS...31.1052A |s2cid=46204216 |url=https://digital.library.unt.edu/ark:/67531/metadc785933/}} This is also available at {{cite journal|url=http://www.osti.gov/energycitations/servlets/purl/823201-oEL59M/native/823201.pdf |title=Energy Citations Database (ECD)|journal=IEEE Transactions on Plasma Science|volume=31|issue=5|pages=1052–1059|access-date=September 5, 2008|doi=10.1109/TPS.2003.815476|year=2003|last1=Anders|first1=A.|bibcode=2003ITPS...31.1052A|s2cid=46204216 }}
• {{cite book |last1=Cooray |first1=Vernon |title=An Introduction to Lightning|date=2014|publisher=Springer Verlag|isbn=978-94-017-8937-0|doi=10.1007/978-94-017-8938-7|s2cid=127691542 }}
• {{cite web |author1=Field, P. R. |author2=W. H. Hand |author3=G. Cappelluti |display-authors=etal |url=http://www.easa.europa.eu/safety-and-research/research-projects/docs/large-aeroplanes/EASA.2008_5.pdf |date=November 2010 |title=Hail Threat Standardisation |publisher=European Aviation Safety Agency |url-status=dead |archive-url=https://web.archive.org/web/20131207052634/http://www.easa.europa.eu/safety-and-research/research-projects/docs/large-aeroplanes/EASA.2008_5.pdf |archive-date=December 7, 2013 |id=Research Project EASA.2008/5}}
• {{cite journal |last=Gosline |first=Anna |title=Thunderbolts from space|journal=New Scientist|date=May 2005|url=https://www.newscientist.com/article/mg18624981.200 |volume=186|issue=2498|pages=30–34}} [http://assets.cambridge.org/052158/3276/sample/0521583276WS.pdf Sample], in .PDF form, consisting of the book through page 20.
• {{Cite news |title=Effects of Lightning |url=http://www.gutenberg.org/ebooks/12873 |work=The Mirror of Literature, Amusement, and Instruction |location=Columbia College, New York |volume=12 |issue=323 |date=July 19, 1828 |via=Project Gutenberg}} Early lightning research.

{{Wikiquote}}

{{commons and category|Lightning}}

{{Wiktionary}}

• {{cite EB1911|wstitle=Lightning |volume=16 |page=673 |short=x}}
• [https://wwlln.net World Wide Lightning Location Network]
• [https://feynmanlectures.caltech.edu/II_09.html#Ch9-S6 Feynman's lecture on lightning]

{{Meteorological variables}}

{{Atmospheric electricity}}

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