Lightning is a massive electrostatic discharge between the electrically charged regions within clouds or between a cloud and the Earth's surface. The charged regions within the atmosphere temporarily equalize themselves through a lightning flash, commonly referred to as a strike if it hits an object on the ground. There are three primary types of lightning; from a cloud to itself (intra-cloud or IC); from one cloud to another cloud (CC) and between a cloud and the ground (CG). Although lightning is always accompanied by the sound of thunder, distant lightning may be seen but be too far away for the thunder to be heard.
Lightning occurs approximately 40–50 times a second worldwide, resulting in nearly 1.4 billion flashes per year.
Many factors affect the frequency, distribution, strength and physical properties of a "typical" lightning flash in a particular region of the world. These factors include ground elevation, latitude, prevailing wind currents, relative humidity, proximity to warm and cold bodies of water, etc. To a certain degree, the ratio between IC, CC and CG lightning may also vary by season in middle latitudes.
Because human beings are terrestrial and most of their possessions are on the Earth, where lightning can damage or destroy them, CG lightning is the most studied and best understood of the three types, even though IC and CC are more common types of lightning. Lightning's relative unpredictability limits a complete explanation of how or why it occurs, even after hundreds of years of scientific investigation.
A typical cloud to ground lightning flash culminates in the formation of an electrically conducting plasma channel through the air in excess of 5 kilometres (3.1 mi) tall, from within the cloud to the ground's surface. The actual discharge is the final stage of a very complex process. A typical thunderstorm has three or more strikes to the Earth per minute at its peak.
Lightning primarily occurs when warm air is mixed with colder air masses, resulting in atmospheric disturbances necessary for polarizing the atmosphere. However, it can also occur during dust storms, forest fires, tornadoes, volcanic eruptions, and even in the cold of winter, where the lightning is known as thundersnow. Hurricanes typically generate some lightning, mainly in the rainbands as much as 160 kilometres (99 mi) from the center.
The science of lightning is called fulminology, and the fear of lightning is called astraphobia.
The first process in the generation of lightning generation is the separation of positive and negative charges within a cloud. Ice crystals inside cumulonimbus clouds rub against one another due to the strong updrafts in these clouds, thus building up a strong static charge.
Positively charged crystals tend to rise to the top causing the cloud top to build up a positive static charge and negatively charged crystals and hailstones drop to the middle and bottom layers of the cloud building up a negative static charge. Cumulonimbus clouds that do not produce enough ice crystals usually fail to produce enough static electricity to cause lightning.
Lightning can also occur as a result of volcanic eruptions or violent forest fires which generate sufficient dust to create a static charge.
The second process is the build up of positive charges on the ground beneath the clouds. The Earth is normally negatively charged with respect to the atmosphere. But as the thunderstorm passes over the ground, the negative charges at the bottom of the cumulonimbus cloud cause the positive charges on the ground to gather along the surface for several miles around the storm and becomes concentrated in vertical objects including trees and tall buildings. If you feel your hair stand up on end in a lightning storm beware. The negative charges from the cloud are pulling the positive charges inside your body to the top of your head and you could be in danger of being struck.
The third process is the generation of the lightning. When sufficient negatives and positives gather in this way, an electrical discharge occurs within the clouds or between the clouds and the ground, producing the bolt.
A bolt of lightning usually begins when an invisible negatively charged stepped leader stroke is sent out from the cloud. As it does so, a positively charged streamer is sent out from the positively charged ground or cloud. When the leader and streamer meet, the electrical discharge takes place up the streamer into the cloud. This return stroke is the most luminous part of the strike, and the part that is really visible.
Most lightning strikes usually last about a quarter of a second. Sometimes several strokes will travel up and down the same leader strike, causing a flickering effect. Thunder is caused when the discharge rapidly super heats the air around the strike, causing a shock wave to be sent out.
Research published in 2002 indicates that every lighting bolt also causes a similar but weaker electrodynamic pulse in the mesosphere, located 50 to 80 km (31 to 53 miles) above the earth, and above into the thermosphere.
This type of lightning is known as negative lightning due to the discharge of negative charge from the cloud, and accounts for over 95% of all lightning.
Statistics: an average bolt of negative lightning carries a current of 30 kiloamperes, transfers a charge of 5 coulombs, has a potential difference of about 100 megavolts, and lasts a few milliseconds.
Positive lightning makes up less than 5% of all lightning. It occurs when the stepped leader forms at the positively charged cloud tops, with the consequence that a positively charged streamer issues from the ground. The overall effect is a discharge of positive charges to the ground.
Research carried out after the discovery of positive lightning in the 1970s showed that positive lightning bolts are typically six to ten times more powerful than negative bolts, last around ten times longer, and can strike several miles distant from the clouds. During a positive lighting strike, huge quantities of ELF and VLF radio waves are generated.
As a result of their power, positive lightning strikes are considerably more dangerous. At the present time aircraft are not designed to withstand such strikes, since their existence was unknown at the time standards were set, and the dangers unappreciated until the destruction of a glider in 1999. It has since been suggested that it may have been positive lightning that caused the crash of Pan Am flight 214 in 1963. Positive lighting is now also thought to be responsible for many forest fires.
Positive lightning has also been shown to trigger the occurrence of upper atmospheric lightning. It tends to occur more frequently in winter storms and at the end of a thunderstorm.
Statistics (based on a small number of measurements): an average bolt of positive lightning carries a current of 300,000 amperes, transfers a charge of up to 300 coulombs, has a potential difference up to 1 gigavolt (a thousand million volts), and lasts for tens or hundreds of milliseconds.
Bipolar lightning occurs when bolts of negative and positive lightning alternately use the same channel through the air.
Some lightning strikes take on particular characteristics, and scientists and the public have given names to these various types of lightning.
Intracloud lightning is the most common type of lightning which occurs completely inside one cumulonimbus cloud, jumping between different charged regions within the cloud. Intracloud lightning is commonly known as sheet lightning because it lights up the cloud and the surrounding sky with an apparent sheet of light. One special type of intracloud lightning is commonly called an anvil crawler. Discharges of electricity in anvil crawlers travel up the sides of the cumulonimbus cloud branching out at the anvil top.
Cloud-to-ground lightning is a great lightning discharge between a cumulonimbus cloud and the ground initiated by the downward-moving leader stroke. This is the second most common type of lightning. One special type of cloud-to-ground lightning is anvil lightning, a form of positive lightning, since it emanates from the anvil top of a cumulonimbus cloud where the ice crystals are positively charged, and is a form of positive lightning. In anvil lightning, the leader stroke issues forth in a nearly horizontal direction till it veers toward the ground. These usually occur miles ahead of the main storm and will strike without warning on a sunny day. They are signs of an approaching storm.
Another special type of cloud-to-ground lightning is bead lightning. This is a regular cloud-to-ground stroke that contains a higher intensity of luminosity. When the discharge fades it leaves behind a string of beads effect for a brief moment in the leader channel. A third special type of cloud-to-ground lightning is ribbon lightning. These occur in thunderstorms where there are high cross winds and multiple return strokes. The winds will blow each successive return stroke slightly to one side of the previous return stoke, causing a ribbon effect. The last special type of cloud-to-ground lightning is staccato lightning which is nothing more than a leader stroke with only one return stroke.
Cloud-to-cloud lightning is a somewhat rare type of discharge lightning between two or more completely separate cumulonimbus clouds.
Ground-to-cloud lightning is a lightning discharge between the ground and a cumulonimbus cloud from an upward-moving leader stroke. Most ground-to-cloud lightning occurs off of tall buildings, mountains and towers.
Heat lightning is nothing more than the faint flashes of lightning on the horizon from distant thunderstorms. Heat lightning was named because it often occurs on hot summer nights. Heat lightning can be an early warning sign that thunderstorms are approaching. In Florida, heat lightning is often seen out over the water at night, the remnants of storms that formed during the day along a sea breeze front coming in from the opposite coast.
Reports by scientists of strange lightning phenomena above storms date back to at least 1886, however it is only in recent years that fuller investigations have been made.
Sprites are now well documented electrical discharges that occur high above the cumulonimbus cloud of an active thunderstorm. They appear as luminous reddish-orange neon-like flashes, last longer than normal lower stratospheric discharges (typically around 17 milliseconds), and are usually spawned by discharges of positive lightning between the cloud and the ground.
Sprites usually occur in clusters of two or more simultaneous vertical discharges, typically extending from 65 to 75 km (40 to 47 miles) above the earth, with or without less intense filaments reaching above and below. Sprites are preceded by a sprite halo that forms due to heating and ionization less than 1 milisecond before the sprite.
Sprites were first photographed on July 6, 1989, by scientists from the University of Minnesota and named after the mischievous sprites in the plays of Shakespeare. They are caused by the electric field of a lighting stroke - as opposed to the electromagnetic pulse that causes a sprite.
Recent research carried out at the University of Houston in 2002 indicates that some normal (negative) lighting discharges produce a sprite halo, the precursor of a sprite, and that every lightning bolt between cloud and ground attempts to produce a sprite or a sprite halo.
Otherworldly Photos Capture Mysterious Phenomena in Upper Atmosphere Wired - July 23, 2013
In the blink of an eye, an enormous bright red light flashes above a thundercloud, spreading energetic branches that extend five times taller than Mount Everest and look like jellyfish tendrils and angel's wings. These mysterious phenomena are known as Transient Luminous Events (TLEs), and are usually invisible to the naked eye because they happen on millisecond timescales, too fast to be seen. They occur between 50 to 100 kilometers above the ground, a long-ignored area of the atmosphere that is too high for aircraft but too low for satellites to investigate. There, the thin air interacts with strong electrical fields to ionize molecules and create arcing plasmas.
Giant Red Sprite Seen From Space Station National Geographic - July 13, 2012
Orbiting above a storm recently, International Space Station astronauts captured a rarely seen type of sky show on camera: a fleeting electrical burst called a red sprite. The red sprite's exceptional size (in a word, giant), plus the resolution and sense of scale in the picture distributed by NASA this week have experts intrigued, despite the fact that red sprites have been seen from space before.
Lightning sprites are out-of-this-world PhysOrg - November 21, 2011
Only a few decades ago, scientists discovered the existence of "sprites" 30 to 55 miles above the surface of the Earth. They're offshoots of electric discharges caused by lightning storms, and a valuable window into the composition of our atmosphere. Now researchers at Tel Aviv University say that sprites are not a phenomenon specific to our planet.
Lightning Creates Particle Accelerators Above Earth National Geographic - April 21, 2010
Mysterious "Sprites" Light Shows Captured on Film National Geographic - June 19, 2007
Blink during a thunderstorm and you may miss the unusual phenomenon of "sprites" - resplendent bursts of light that, for less than a second, burn brighter than Venus. These brief explosions, which can outshine everything except for the sun and moon, are so fleeting, that scientists still don't know much about how they work.
Video Reveals 'Sprite' Lightning Secrets Live Science - June 12, 2007
Sprites dance high above thunderstorms, but they’re not furtive mythical creatures. They’re quick bursts of electricity that have left atmospheric scientists in the dark about their origins. New ultra-high-speed video shows sprites form as fast-paced balls of electricity, not streaks or tendrils as previous footage suggested. The discovery challenges current theories of how mysterious sprites form and could lead to new understanding of atmospheric chemistry.
Ice Lightning - Clouds with more ice produced more lightning Live Science - August 13, 2005
High-altitude light show in focus BBC - July 2004
Photos of red sprites, blue jets, elves and sprite halos are now flowing into the University of California, Berkeley's Space Sciences Laboratory from the first satellite instrument devoted to the study of these puzzling high-altitude lightning flashes. Blue jets differ from sprites in that they project from the top of the cumulonimbus above a thunderstorm, typically in a narrow cone, to the lowest levels of the ionosphere 40 to 50 km (25 to 30 miles) above the earth. They are also brighter than sprites and, as implied by their name, are blue in color. They were first recorded on October 21, 1989 on a video taken from the space shuttle as it passed over Australia.
Elves appear as a dim, flattened expanding glow around 400 km (250 miles) in diameter that lasts for, typically, just one millisecond. They occur in the ionosphere 100 km (60 miles) above the ground over thunderstorms. Their color was a puzzle for some time, but is now believed to be a red hue.
Elves were first recorded on another shuttle mission, this time recorded off French Guiana on October 7, 1990. Elves is a frivolous acronym for Emissions of Light and Very Low Frequency Perturbations From Electromagnetic Pulse Sources. This refers to the process by which the light is generated; the excitation of nitrogen molecules due to electron collisions (the electrons having been energized by the electromagnetic pulse caused by a positive lightning bolt.
On September 14, 2001, scientists at the Arecibo Observatory photographed a huge jet double the height of those previously observed, reaching around 80 km (50 miles) into the atmosphere. The jet was located above a thunderstorm over the ocean, and lasted under a second. Lightning was initially observed traveling up at around 50,000 m per second in a similar way to a typical blue jet, but then divided in two and speeded to 250,000 m / second to the ionosphere, where they spread out in a bright burst of light.
On July 22, 2002 five gigantic jets between 60 and 70 km (35 to 45 miles) in length were observed over the South China Sea from Taiwan, reported in Nature. The jets lasted under a second, with shapes likened by the researchers to giant trees and carrots.
Researchers have speculated that such forms of upper atmospheric lightning may play a role in the formation of the ozone layer.
All lightning is streak lighting. This is nothing more than the return stroke, the visible part of the lightning stroke. Because most of these strokes occur inside a cloud, we do not see many of the individual return strokes in a thunderstorm.
Lightning has been triggered in several instances. Lightning struck the Apollo 12 soon after takeoff, and has struck soon after thermonuclear explosions. For more information, see triggered lightning.
Lightning has been observed on other planets, such as Venus and Jupiter, and electrical discharges between Jupiter and Io often occur.
Lightning on Jupiter is estimated to be 100 times as powerful, but fifteen times rarer, than that which occurs on Earth.
Lightning on Venus occurs so often that it is speculated that, were colonization to ever occur on Venus, lightning would be a primary power source.
Cassini sees lightning in Saturn's atmosphere BBC - July 2004
A bolt of lightning can reach temperatures approaching 28,000 kelvin (or about 50,000 degrees Fahrenheit) in a split second. This is many times hotter than the surface of the sun. A result of this is that lightning strikes that hit a loose soil or sandy region of the ground may fuse the soil or sand into channels called fulgurites.
These fulgurites are sometimes found under the sandy surfaces of beaches and golf courses or in desert regions. It is one evidence that lightning spreads out into branching channels when it strikes the ground.
Lightning is responsible for approximately 100 deaths a year in the United States alone. Lightning ranks second only to floods for storm related casualties in the U.S. every year. Many of these deaths could be prevented if basic precautions were taken when thunderstorms are expected in an area. Listening to a radio to keep up to date on storms in the area is the best way to prepare for safety.
One way to prepare for lightning safety is to install a device known as lightning conductor (commonly known as a lightning rod) for preventing damage by lightning to a building. A lightning conductor is a metal spike that is connected to earth by a low-resistance path. Should lightning strike a building, the current will travel through the conductor rather than through the fabric of the building, causing less damage.
Electrical equipment can be protected from lightning by a lightning arrester. This is a device that contains one or more gas-filled spark gaps between the equipment's cables and earth. Should lightning strike one of the cables, the high voltage will cause the gas in the spark gap to break down and become a conductor, providing a path for the lightning to reach the ground without passing through the equipment.
No place is truly 100% safe in a thunderstorm, but some places are more safe than others. Larger, better constructed structures are better than smaller or more open structures. Fully enclosed metal vehicles with the windows rolled up are good shelters, providing that no contact is made with any exposed metal inside or outside the vehicle.
When outside, avoid the following:
If you find yourself trapped in an open area during a storm, position yourself close to the ground by squatting with your feet close together and on the balls of your feet. Crouch in a ditch if possible. Avoid proximity to other people (minimum 5 meters or 15 feet). Since lightning spreads when it hits the ground, you want to minimize as much surface area between you and the ground. Remember, humans are good conductors of electricity, lightning tends to strike at the highest thing in an area, because electricity will always take the path of least resistance.
What's It Feel Like to Be Struck by Lightning, and How Can You Avoid It? ABC - July 18, 2004
When inside avoid the following:
Lightning is often considered a divine or supernatural phenomenon. In many mythologies, it plays a role, and often have an affiliation with a certain god.
In Greek mythology lightning and thunder are weapons of Zeus, given from Cyclopes.
In Mayan mythology Huracan is sometimes represented as three lightning bolts.
In Norse mythology Odin's spear Gungnir is an embodiment of lightning. In addition, his son, Thor is specifically the God of Thunder and Lightning
In Native American mythology, the Ani Hyuntikwalaski ("Thunder Beings") are beings that cause lightning fire in a hollow sycamore tree.
In movies and comics of the contemporary U.S. and many other countries, the lightning is often employed as an omnious, dramatic sign. It may herald a waking of a great evil or emergence of a crisis. Various novels and role playing games with fantasy tint involves wizardry of lightning bolt, weapon embodying the power of lightning, etc. The comic book character Billy Batson changed into the superhero Captain Marvel by saying the word, "Shazam!" which called down a bolt of magic lightning to strike to change.
Incredible Technology: How to Map a Lightning Strike Live Science - October 14, 2013
Some scientists literally spend their time waiting for lightning to strike. Lightning is the second highest cause of annual weather-related deaths in the United States, according to the National Weather Association. It starts fires, causes power outages and wreaks havoc on electronics systems. The science of lightning detection has improved dramatically since Ben Franklin flew his kite in a thunderstorm in 1752. Researchers can now predict conditions that precede a bolt from the blue, and track the location and strength of a strike while it's occurring. There is no more iconic storm image than the brilliant white forks of lightning snaking their way across a menacing sky. But most of it happens too fast for the human eye to glimpse, so researchers use high-speed cameras to spy how the lightning races between sky and Earth.
When lightning first develops, it generally sends a bolt called a step leader down toward the ground, branching in seemingly random directions. When the bolt gets close to the ground, it creates an intense electric field, which causes upward streamers that meet it midair. After the streamers attach to the main bolt, the lightning charges down again in a dart leader, which is the bright part observers on the ground actually see.
Sakurajima Volcano with Lightning NASA - March 11, 2013
Why does a volcanic eruption sometimes create lightning? Pictured above, the Sakurajima volcano in southern Japan was caught erupting in early January. Magma bubbles so hot they glow shoot away as liquid rock bursts through the Earth's surface from below. The above image is particularly notable, however, for the lightning bolts caught near the volcano's summit. Why lightning occurs even in common thunderstorms remains a topic of research, and the cause of volcanic lightning is even less clear. Surely, lightning bolts help quench areas of opposite but separated electric charges. One hypothesis holds that catapulting magma bubbles or volcanic ash are themselves electrically charged, and by their motion create these separated areas. Other volcanic lightning episodes may be facilitated by charge-inducing collisions in volcanic dust. Lightning is usually occurring somewhere on Earth, typically over 40 times each second.
Earth's Tallest Lightning Seen in Unprecedented Detail Live Science - July 28, 2011
Mysterious and gigantic jets of lightning that shoot up to near the edge of space have now been observed in unprecedented detail, revealing just how much charge they pack and how they form. More than 50 miles (80 kilometers) above Earth's surface, extreme ultraviolet radiation from the sun reacts with air molecules to produce highly charged particles, generating an energetic region known as the ionosphere.In 2001, scientists discovered gigantic jets of lightning arcing up from clouds in the lowest portion of the atmosphere, the troposphere, to the ionosphere. These rarities apparently are caused by the profound difference in electric charge between the ionosphere and the rest of the atmosphere, but much else about them remained unclear.
Giant natural particle accelerator discovered above thunderclouds PhysOrg - April 14, 2010
A lightning researcher at the University of Bath has discovered that during thunderstorms, giant natural particle accelerators can form 40 km above the surface of the Earth.
Lightning really does make mushrooms multiply PhysOrg - April 13, 2010
Japanese farming folklore has it that lightning makes mushrooms multiply, and new research supports the idea. Mushrooms form a staple part of the diet in Japan, and the fungi are in such high demand that around 50,000 tons are imported annually, so scientists have been experimenting with artificial lightning to see if it could increase the crop.
One Mystery of Sandstorm Lighting Explained Live Science - April 13, 2010
Sandstorms can generate spectacular lightning displays, but how they do so is a mystery. By unlocking the secrets of how sparks come to fly in these storms as researchers are now doing, scientists could help grapple with all kinds of problems, from charged particle clouds that can cause devastating explosions in the food, drug and coal industries to charged dust that could obscure vital solar panels on missions to the moon or Mars. Sand is an insulator, so seeing sandstorms generate lightning would be somewhat like watching electricity emerge from a storm full of rubber balls. It has been an enigma for more than 150 years as to how sand grains can transfer the huge amounts of electrical charge needed for lightning to happen.
Lightning's mirror image... only much bigger PhysOrg - August 23, 2009
With a very lucky shot, scientists have captured a one-second image and the electrical fingerprint of huge lightning that flowed 40 miles upward from the top of a storm.
Gigantic Lightning Jets Shoot from Clouds to Space Live Science - August 23, 2009
Strokes of lightning flashing down towards the ground are a familiar sight during summer thunderstorms, but scientists have capture an image of a rare lightning bolt shooting out upwards from a cloud, almost to the edge of the Earth's atmosphere. These bolts of upwards lightning, one type among a variety of electrical discharges now known to occur above thunderstaorms, are called gigantic jets, and were only first discovered in 2001. Since then, only about 10 gigantic jets have been observed, said Steven Cummer, who was part of the team that photographed this most recent jet. Gigantic jets are essentially the same as cloud-to-ground lightning, only they go the opposite way.
Lightning Remains Huge Mystery Live Science - July 18, 2008
As common as lightning is, it still sparks considerable confusion among scientists. Many of the basics are understood, but researchers admit they don't really understand how lightning gets from there to here. And they're totally baffled by lightning's link to X-rays, a discovery made back in 2001. "Nobody understands how lightning makes X-rays," says Martin Uman, a professor of electrical and computer engineering at the University of Florida. "Despite reaching temperatures five times hotter than the surface of the sun, the temperature of lightning is still thousands of times too cold to account for the X-rays observed."
Lightning Strikes Deadliest In Summer Science Daily - June 29, 2007
Lightning strikes were responsible for 47 confirmed deaths and 246 confirmed injuries last year, according to the National Oceanic and Atmospheric Administration, and summer is the peak season for lightning-related injuries.
Noxious Lightning NASA - April 27, 2007
Lightning is more than light and noise: It's an intense chemical factory that affects both local air quality and global climate. But how big is the effect? Researchers aren't sure. To answer the question they're developing a new technique to estimate the factory's output. Atmospheric chemists are very interested in trace gases produced by lightning, particularly nitrogen oxides ('NOx' for short).
Arkansas Lightning Daily Mail - July 2006
When a rainbow formed in the sky people stopped and stared at the natural wonder. But then lightning sparked across the evening panorama as two of nature's most spectacular phenomenon created an unusual alliance. The clash of weather was seen above Fort Smith, Arkansas. The intracloud lightning, known as an anvil crawler, is the most common form of lightning, with the electrical charge contained within a single cumulonimbus cloud. Lightning often occurs during heavy storms while rainbows are generally formed after the rain has stopped, making an appearance of both simultaneously relatively rare. The actual electric charge in a flash of lightning comes from particles from the sun sent out in the solar wind which gather in the outer atmospheric layers before creating a strike. Scientists are still divided by what actually causes lightning, with one theory suggesting falling droplets of ice and rain become electrically polarized as they fall through the natural electric field in the Earth's atmosphere. This would explain why lightning often accompanies storms and heavy rain. The same droplets also cause the rainbow, when light from the sun is refracted by the water to cause a spectrum.
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