Every second, approximately 700 lightning, and every year about 3000 people die due to lightning strikes. The physical nature of lightning has not been fully explained, and most people have only a rough idea of what it is. Some discharges collide in the clouds, or something like that. Today we turned to our physics writers to learn more about the nature of lightning. How lightning appears, where lightning strikes, and why thunder thunders. After reading the article, you will know the answer to these and many other questions.
What is lightning
Lightning– spark electric discharge in the atmosphere.
Electric discharge is the process of current flow in a medium associated with a significant increase in its electrical conductivity relative to the normal state. There are different types electrical discharges in gas: spark, arc, smoldering.
A spark discharge occurs at atmospheric pressure and is accompanied by a characteristic spark crack. A spark discharge is a set of filamentary spark channels that disappear and replace each other. Spark channels are also called streamers. The spark channels are filled with ionized gas, that is, plasma. Lightning is a giant spark, and thunder is a very loud crack. But it's not that simple.
Physical nature of lightning
How is the origin of lightning explained? System cloud-ground or cloud-cloud It is a kind of capacitor. The air plays the role of a dielectric between the clouds. The bottom of the cloud has a negative charge. When there is a sufficient potential difference between the cloud and the ground, conditions arise in which lightning occurs in nature.
Step leader
Before the main flash of lightning, a small spot can be observed moving from the cloud to the ground. This is the so-called stepped leader. Electrons, under the influence of a potential difference, begin to move towards the ground. As they move, they collide with air molecules, ionizing them. A kind of ionized channel is laid from the cloud to the ground. Due to the ionization of air by free electrons, the electrical conductivity in the leader’s trajectory zone increases significantly. The leader, as it were, paves the way for the main discharge, moving from one electrode (cloud) to another (ground). Ionization occurs unevenly, so the leader can branch.
Backfire
The moment the leader approaches the ground, the tension at his end increases. A response streamer (channel) is thrown out from the ground or from objects protruding above the surface (trees, roofs of buildings) towards the leader. This property of lightning is used to protect against it by installing a lightning rod. Why does lightning strike a person or a tree? In fact, she doesn't care where to hit. After all, lightning seeks the shortest path between earth and sky. This is why it is dangerous to be on the plain or on the surface of the water during a thunderstorm.
When the leader reaches the ground, current begins to flow through the laid channel. It is at this moment that the main lightning flash is observed, accompanied by a sharp increase in current strength and energy release. The relevant question here is, where does the lightning come from? It is interesting that the leader spreads from the cloud to the ground, but the opposite bright flash, which we are used to seeing, spreads from the ground to the cloud. It is more correct to say that lightning does not come from heaven to earth, but occurs between them.
Why does lightning thunder?
Thunder results from a shock wave generated by the rapid expansion of ionized channels. Why do we first see lightning and then hear thunder? It's all about the difference between the speeds of sound (340.29 m/s) and light (299,792,458 m/s). By counting the seconds between thunder and lightning and multiplying them by the speed of sound, you can find out at what distance from you the lightning struck.
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Types of lightning and facts about lightning
Lightning between sky and earth is not the most common lightning. Most often, lightning occurs between clouds and does not pose a threat. In addition to ground-based and intra-cloud lightning, there is lightning that forms in the upper layers of the atmosphere. What types of lightning are there in nature?
- Intracloud lightning;
- Ball lightning;
- "Elves";
- Jets;
- Sprites.
The last three types of lightning cannot be observed without special instruments, since they are formed at an altitude of 40 kilometers and above.
Here are some facts about lightning:
- The length of the longest recorded lightning on Earth was 321 km. This lightning was spotted in Oklahoma 2007.
- The longest lightning lasted 7,74 seconds and was recorded in the Alps.
- Lightning is formed not only on Earth. We know for sure about lightning on Venus, Jupiter, Saturn And Uranus. Saturn's lightning is millions of times more powerful than Earth's.
- The current strength in lightning can reach hundreds of thousands of amperes, and the voltage can reach billions of volts.
- The temperature of the lightning channel can reach 30000 degrees Celsius is in 6 times the surface temperature of the Sun.
Ball lightning
Ball lightning – separate species lightning, the nature of which remains a mystery. Such lightning is a luminous object in the shape of a ball moving in the air. According to limited evidence, ball lightning can move along an unpredictable trajectory, split into smaller bolts, explode, or simply disappear unexpectedly. There are many hypotheses about the origin of ball lightning, but none can be considered reliable. Fact - no one knows how ball lightning appears. Some hypotheses reduce the observation of this phenomenon to hallucinations. Ball lightning has never been observed in laboratory conditions. All scientists can be content with is eyewitness accounts.
Finally, we invite you to watch the video and remind you: if a coursework or test falls on your head like lightning on a sunny day, there is no need to despair. Student service specialists have been helping students since 2000. Seek qualified help at any time. 24 hours a day, 7 days a week we are ready to help you.
Everyone knows what a thunderstorm is - the flash of lightning and the roar of thunder. Many people (especially children) are even very afraid of her. But where do thunder and lightning come from? And in general, what kind of phenomenon is this?
A thunderstorm is indeed a rather unpleasant and even eerie natural phenomenon, when dark, heavy clouds cover the sun, lightning flashes, thunder rumbles, and rain pours from the sky in torrents...
And the sound that arises is nothing more than a wave caused by strong air vibrations. In most cases, the volume increases towards the end of the roll. This occurs due to the reflection of sound from clouds. This is thunder.
Lightning is a very powerful electrical discharge of energy. It occurs as a result of strong electrification of clouds or the earth's surface. Electrical discharges occur either in the clouds themselves, or between two adjacent clouds, or between a cloud and the ground. The process of lightning occurrence is divided into the first strike and all subsequent strikes. The reason is that the very first lightning strike creates a path for electrical discharge. A negative electrical discharge accumulates at the bottom of the cloud. And the earth's surface has a positive charge. Therefore, electrons (negatively charged particles, one of the basic units of matter) located in a cloud are attracted to the ground like a magnet and rush down. As soon as the first electrons reach the surface of the earth, a channel (a kind of passage) free for the passage of electrical discharges is created, through which the remaining electrons rush down. Electrons near the ground are the first to leave the channel. Others are rushing to take their place. As a result, a condition is created in which all the negative energy discharge comes out of the cloud, creating a powerful flow of electricity directed into the ground.
It is at such a moment that a flash of lightning occurs, which is accompanied by peals of thunder. Electrified clouds create lightning. But not every cloud contains enough power to penetrate the atmospheric layer. Certain circumstances are necessary for the manifestation of force and elements.
A cloud whose height reaches several thousand meters can be considered a thunderstorm. The bottom of the cloud is located near the earth's surface, the temperature regime there is higher than in the upper part of the cloud, where water droplets can freeze. Air masses are in constant motion. Warm air goes up, and cold air goes down. When particles move, they become electrified, that is, they are saturated with electricity. Different parts of the cloud accumulate different amounts of energy. When there is too much of it, a flash occurs, accompanied by peals of thunder. This is a thunderstorm. What types of lightning are there? Someone might think that lightning is all the same, that a thunderstorm is a thunderstorm. However, there are several types of lightning that are very different from each other. Linear lightning is the most common type. It looks like an overgrown tree upside down. Several thinner and shorter “shoots” extend from the main canal (trunk).
The length of such lightning can reach up to 20 kilometers, and the current strength can be 20,000 amperes. Its speed is 150 kilometers per second. The temperature of the plasma filling the lightning channel reaches 10,000 degrees. Intracloud lightning - the occurrence of this type is accompanied by changes in electric and magnetic fields, and the emission of radio waves. Such lightning is most likely to be found closer to the equator. In temperate climates it appears extremely rarely. If there is lightning in the cloud, then a foreign object that violates the integrity of the shell, for example, an electrified aircraft, can force it to come out. Its length can vary from 1 to 150 kilometers. Ground lightning - This is the longest-lasting type of lightning, so its consequences can be devastating.
Since there are obstacles on its way, in order to get around them, the lightning is forced to change its direction. Therefore, it reaches the ground in the form of a small staircase. Its speed is approximately 50 thousand kilometers per second. After the lightning has completed its path, it stops moving for several tens of microseconds, and its light weakens. Then the next stage begins: repeating the traversed path.
The most recent discharge exceeds all previous ones in brightness, and the current strength in it can reach hundreds of thousands of amperes. The temperature inside the lightning fluctuates around 25,000 degrees. Sprite lightning. This variety was discovered by scientists relatively recently - in 1989. This lightning is very rare and was discovered completely by accident. Moreover, it lasts only some tenths of 1 second. What distinguishes Sprite from other electrical discharges is the height at which it appears - approximately 50-130 kilometers, while other types do not overcome the 15-kilometer mark. In addition, sprite lightning is distinguished by its huge diameter, which can reach 100 km. Such lightning looks like a vertical column of light and flashes not individually, but in groups. Its color can be different and depends on the composition of the air: closer to the ground, where there is more oxygen, it is green, yellow or white. And under the influence of nitrogen, at an altitude of more than 70 km, it acquires a bright red hue.
Pearl lightning. This lightning, like the previous one, is a rare natural phenomenon. Most often, it appears after the linear one and completely repeats its trajectory. It consists of balls located at a distance from each other and resembling beads. Ball lightning. This is a special variety. Natural phenomenon when lightning is in the shape of a ball, shining and floating across the sky. In this case, its flight path becomes unpredictable, which makes it even more dangerous for humans.
In most cases, ball lightning occurs in combination with other types. However, there are cases when it appeared even in sunny weather. The size of the ball can be from ten to twenty centimeters.
Its color can be blue, orange or white. And the temperature is so high that if the ball suddenly ruptures, the liquid surrounding it evaporates, and metal or glass objects melt. A ball of such lightning can exist for quite a long time. When moving, it can unexpectedly change its direction, hover in the air for several seconds, or sharply deviate to one side. It appears in one copy, but always unexpectedly. The ball may descend from the clouds, or suddenly appear in the air from behind a pole or tree. And if ordinary lightning can only strike something - a house, a tree, etc., then ball lightning can penetrate into a closed space (for example, a room) through an outlet, or switched on household appliances- TV, etc.
Which lightning is considered the most dangerous?
Usually the first strike of thunder and lightning is followed by a second. This is due to the fact that the electrons in the first flash create the opportunity for a second passage of electrons. Therefore, subsequent outbreaks occur one after another with almost no time intervals, striking the same place.
Lightning emerging from a cloud with its electric discharge can cause serious harm to a person and even kill. And even if her blow does not hit a person directly, but falls nearby, the health consequences can be very bad. To protect yourself, you must follow some rules: So, during a thunderstorm, you should never swim in the river or sea! You must always be on dry land.
In this case, it is necessary to be as close to the surface of the earth as possible. That is, there is no need to climb a tree, much less stand under it, especially if there is one in the middle of an open place. In addition, you should not use any mobile devices (phones, tablets, etc.) because they can attract lightning.
Among the many atmospheric phenomena, lightning undoubtedly occupies a special place. She is extremely beautiful and spectacular, and the incredible power of her blows still terrifies many people today.
And this despite the fact that they all studied at school and have an idea of what electricity is.
Ancient ideas about lightning
In ancient times, lightning evoked equally strong feelings in people. She was admired and feared, considering her a weapon of the gods. It is not for nothing that the most formidable and warlike deities of almost all nations were armed with lightning: Zeus among the ancient Greeks, Jupiter among the Romans, Perun among the Slavs.
In the ancient Indian pantheon of gods, Shiva the Destroyer and Indra the Warrior were armed with lightning, who even had a special weapon for throwing lightning - a vajra.
At the same time, lightning was often considered a symbol of the awakening of vitality and energy. Thus, according to the beliefs of the ancient Chinese, the weather was controlled by a special heavenly council of four gods.
Lightning was in charge of the goddess Dian-mu, who brought the heavenly mirrors closer and apart, beginning with a flash of lightning the steady movement of life in the fields and in the hearts of people. In Christianity, lightning symbolizes Divine revelation and Divine judgment.
How is lightning formed?
Today everyone knows that lightning is a powerful electrical discharge that occurs between clouds. But not everyone knows how exactly it is formed. 
A thundercloud is a cloud of water vapor, sometimes measuring tens of kilometers in size. Its upper part can be located at an altitude of 6-7 km, while the lower part is only half a kilometer from the ground.
At an altitude of 4 km, negative temperatures always reign, so droplets of steam there turn into pieces of ice. Moving chaotically, they constantly rub against each other, due to which most of them acquire an electric charge: small ones are positive, large ones are negative.
Under the influence of gravity, large pieces of ice fall into the lower layers of the cloud, accumulating there, while small pieces remain at the top. Gradually, the total value of the charges becomes large enough for the field that arises between them to acquire a gigantic intensity.
When differently charged parts of the cloud come closer, individual ions and electrons, torn from their places by mutual attraction, rush towards each other, dragging their neighbors along with them. A plasma discharge channel appears, spreading through sections of the cloud at a speed of hundredths of a second. 
Sometimes the lower edge of a cloud hangs low enough above the ground for an electrical breakdown to occur between the cloud and the surface of the earth. Particularly “lucky” in this regard are isolated hillocks or trees, poles and towers of power lines, which become catalysts for the discharge. This is why it is dangerous to stay under a lone tree on a hill or an electric pole during a thunderstorm.
The temperature inside the lightning channel reaches ten thousand degrees, and the electrical voltage reaches several hundred million volts. At the same time, the capacity of the cloud “capacitor” is very small - only about 0.15 microfarads. The hot plasma burns the air around the channel, which then collapses, causing a shock wave that we perceive as thunder.
Zarnitsa
Lightning does not only occur in ordinary clouds made of water vapor. For their formation, it is necessary that there be a finely dispersed suspension of any substance in the air, the particles of which will rub against each other and acquire an electrical charge.
So, in a dry summer you can sometimes see a “dry thunderstorm” - lightning formed in huge clouds of wind-raised dust. These lightning bolts are called lightning.
Ball lightning
Sometimes during a thunderstorm, ball lightning is formed - a small spherical clot of energy. This is one of the most poorly studied atmospheric phenomena, which, unlike ordinary lightning, has not yet been replicated in laboratory conditions. 
Ball-shaped lightning can cause harm to the person it touches, but there are many cases when contact with it did not bring any unpleasant sensations.
The electrical nature of lightning was revealed in the research of the American physicist B. Franklin, on whose initiative an experiment was carried out to extract electricity from a thundercloud. Franklin's experience in elucidating the electrical nature of lightning is widely known. In 1750 he published a work in which he described an experiment using kite launched into a thunderstorm. Franklin's experience was described in the work of Joseph Priestley.
The average length of lightning is 2.5 km, some discharges extend up to 20 km in the atmosphere.
How does lightning form? Most often, lightning occurs in cumulonimbus clouds, then they are called thunderstorms. Lightning sometimes forms in nimbostratus clouds, as well as during volcanic eruptions, tornadoes and dust storms.
Scheme of lightning occurrence: a - formation; b - category.
For lightning to occur, it is necessary that in a relatively small (but not less than a certain critical) volume of the cloud, an electric field with a strength sufficient to initiate an electrical discharge (~ 1 MV/m) is formed, and in a significant part of the cloud there is a field with an average strength sufficient to maintain the started discharge (~ 0.1-0.2 MV/m). In the lightning electrical energy clouds turns into heat and light.
Linear lightning is usually observed, which belongs to the so-called electrodeless discharges, since they begin (and end) in accumulations of charged particles. This determines some of their still unexplained properties that distinguish lightning from discharges between electrodes.
Thus, lightning does not occur shorter than several hundred meters; they arise in electric fields much weaker than the fields during interelectrode discharges; The collection of charges carried by lightning occurs in thousandths of a second from billions of small particles, well isolated from each other, located in a volume of several square kilometers.
The most studied process of lightning development in thunderclouds, while lightning can pass in the clouds themselves (intracloud lightning), or can strike the ground (ground lightning).
Ground lightning
Development diagram of ground lightning: a, b - two leader stages; 1 - cloud; 2 - streamers; 3 - step leader channel; 4 - channel crown; 5 - pulse corona on the channel head; c - formation of the main lightning channel (K).
The development process of ground lightning consists of several stages. At the first stage, in the zone where the electric field reaches a critical value, impact ionization begins, created initially by free electrons, always present in small quantities in the air, which, under the influence of electric field acquire significant speeds towards the ground and, colliding with the molecules that make up the air, ionize them.
According to more modern concepts, the discharge is initiated by high-energy cosmic rays, which trigger a process called runaway breakdown. Thus, electron avalanches arise, turning into threads of electrical discharges - streamers, which are well-conducting channels, which, merging, give rise to a bright thermally ionized channel with high conductivity - a stepped lightning leader.
The movement of the leader towards the earth's surface occurs in steps of several tens of meters at a speed of ~ 50,000 kilometers per second, after which its movement stops for several tens of microseconds, and the glow greatly weakens; then, in the subsequent stage, the leader again advances several tens of meters.
A bright glow covers all the steps passed, followed by a stop and weakening of the glow again. These processes are repeated when the leader moves to the surface of the earth from average speed 200,000 meters per second. As the leader moves toward the ground, the field intensity at its end increases, and under its action, a response streamer is ejected from objects protruding on the surface of the Earth, connecting to the leader. This feature of lightning is used to create a lightning rod.
In the final stage, a reverse (from bottom to top), or main, lightning discharge follows along the channel ionized by the leader, characterized by currents from tens to hundreds of thousands of amperes, a brightness noticeably exceeding the brightness of the leader, and a high speed of progress, initially reaching ~ 100,000 kilometers per second , and at the end decreasing to ~ 10,000 kilometers per second.
The channel temperature during the main discharge can exceed 25,000 °C. The length of the lightning channel can be from 1 to 10 km, the diameter can be several centimeters. After the passage of the current pulse, the ionization of the channel and its glow weaken. In the final stage, the lightning current can last hundredths and even tenths of a second, reaching hundreds and thousands of amperes. Such lightning is called prolonged lightning and most often causes fires.
The main discharge often discharges only part of the cloud. Charges located at high altitudes can give rise to a new (swept) leader moving continuously at speeds of thousands of kilometers per second. The brightness of its glow is close to the brightness of the stepped leader. When the swept leader reaches the surface of the earth, a second main blow follows, similar to the first.
Typically, lightning includes several repeated discharges, but their number can reach several dozen. The duration of multiple lightning can exceed 1 second. The displacement of the channel of multiple lightning by the wind creates the so-called ribbon lightning - a luminous strip.
Intracloud lightning
Intracloud lightning usually includes only leader stages; their length ranges from 1 to 150 km. The proportion of intracloud lightning increases as it moves toward the equator, changing from 0.5 in temperate latitudes to 0.9 in the equatorial zone. The passage of lightning is accompanied by changes in electric and magnetic fields and radio emissions, the so-called atmospherics.
The probability of a ground object being struck by lightning increases as its height increases and with an increase in the electrical conductivity of the soil on the surface or at some depth (the action of a lightning rod is based on these factors). If there is an electric field in the cloud that is sufficient to maintain a discharge, but not sufficient to cause it to occur, a long metal cable or an airplane can act as the lightning initiator, especially if it is highly electrically charged. In this way, lightning is sometimes “provoked” in nimbostratus and powerful cumulus clouds.
Every second, about 50 lightning strikes the surface of the earth, and on average, every square kilometer is struck by lightning six times a year.
People and lightning
Lightning is a serious threat to human life. A person or animal being struck by lightning often occurs in open spaces, because... The electric current follows the shortest path "thundercloud-ground". Often lightning strikes trees and transformer installations on railway, causing them to ignite.
It is impossible to be struck by ordinary linear lightning inside a building, but there is an opinion that so-called ball lightning can penetrate through cracks and open windows. Normal lightning is dangerous for television and radio antennas located on the roofs of high-rise buildings, as well as for network equipment.
In the body of lightning victims, the same pathological changes are observed as in case of electric shock. The victim loses consciousness, falls, may experience convulsions, and often stops breathing and heartbeat. You can usually find “current marks” on your body—the places where electricity enters and exits.
These are tree-like light pink or red stripes that disappear when pressed with fingers (they persist for 1-2 days after death). They are the result of the expansion of capillaries in the area of lightning contact with the body. In case of death, the cause of cessation of basic vital functions is the sudden stop of breathing and heartbeat from the direct effect of lightning on the respiratory and vasomotor centers of the medulla oblongata.
When struck by lightning, the first medical care must be urgent. In severe cases (stopping breathing and heartbeat), resuscitation is necessary; it should be provided by any witness to the misfortune without waiting for medical workers. Resuscitation is effective only in the first minutes after a lightning strike; after 10-15 minutes it is, as a rule, no longer effective. Emergency hospitalization is necessary in all cases.
Victims of lightning
In mythology and literature:
- Asclepius (Aesculapius), son of Apollo, the god of doctors and medical art, not only healed, but also revived the dead. To restore the broken world order, Zeus struck him with his lightning;
- Phaeton, the son of the sun god Helios, once undertook to drive his father’s solar chariot, but could not restrain the fire-breathing horses and almost destroyed the Earth in a terrible flame. An angry Zeus pierced Phaeton with lightning.
Historical figures:
- Russian academician G.V. Richman - died from a lightning strike in 1753;
- People's Deputy of Ukraine, ex-governor of the Rivne region V. Chervoniy died from a lightning strike on July 4, 2009.
- Roy Sally Wang survived after being struck by lightning seven times;
- American Major Summerford died after a long illness (the result of being struck by the third lightning). The fourth lightning completely destroyed his monument in the cemetery;
- Among the Andean Indians, a lightning strike is considered necessary to achieve the highest levels of shamanic initiation.
Trees and lightning
Tall trees are frequent targets for lightning. You can easily find multiple lightning scars on long-lived relict trees. A single standing tree is thought to be more likely to be struck by lightning, although in some forested areas lightning scars can be seen on almost every tree. Dry trees catch fire when struck by lightning. Most often, lightning strikes are directed at oak, least often at beech, which apparently depends on the different amounts of fatty oils in them, which represent great resistance to electricity.
Lightning travels through a tree trunk along the path of least electrical resistance, releasing large quantities heat, turning water into steam, which splits the tree trunk or, more often, tears off sections of bark from it, showing the path of lightning.
In subsequent seasons, the trees usually repair the damaged tissue and may close the entire wound, leaving only a vertical scar. If the damage is too severe, wind and pests will eventually kill the tree. Trees are natural lightning conductors and are known to provide protection from lightning strikes to nearby buildings. Tall trees planted near a building catch lightning, and the high biomass of the root system helps ground the lightning strike.
Musical instruments are made from trees struck by lightning, attributing unique properties to them.
Lightning 1882
(c) Photographer: William N. Jennings, c. 1882
The electrical nature of lightning was revealed in the research of the American physicist B. Franklin, on whose idea an experiment was carried out to extract electricity from a thundercloud. Franklin's experience in elucidating the electrical nature of lightning is widely known. In 1750, he published a work that described an experiment using a kite launched into a thunderstorm. Franklin's experience was described in the work of Joseph Priestley.
Physical properties of lightning
The average length of lightning is 2.5 km, some discharges extend up to 20 km in the atmosphere.
Lightning Formation
Most often, lightning occurs in cumulonimbus clouds, then they are called thunderstorms; Lightning sometimes forms in nimbostratus clouds, as well as during volcanic eruptions, tornadoes and dust storms.
Typically observed are linear lightning, which belong to the so-called electrodeless discharges, since they begin (and end) in accumulations of charged particles. This determines some of their still unexplained properties that distinguish lightning from discharges between electrodes. Thus, lightning does not occur shorter than several hundred meters; they arise in electric fields much weaker than the fields during interelectrode discharges; The collection of charges carried by lightning occurs in thousandths of a second from billions of small particles, well isolated from each other, located in a volume of several km³. The most studied process of lightning development in thunderclouds, while lightning can occur in the clouds themselves - intracloud lightning, or they can hit the ground - ground lightning. For lightning to occur, it is necessary that in a relatively small (but not less than a certain critical) volume of the cloud an electric field (see atmospheric electricity) with a strength sufficient to initiate an electrical discharge (~ 1 MV/m) must be formed, and in a significant part of the cloud there would be field with an average strength sufficient to maintain the started discharge (~ 0.1-0.2 MV/m). In lightning, the electrical energy of the cloud is converted into heat, light and sound.
Ground lightning
The development process of ground lightning consists of several stages. At the first stage, in the zone where the electric field reaches a critical value, impact ionization begins, created initially by free charges, always present in small quantities in the air, which, under the influence of the electric field, acquire significant speeds towards the ground and, colliding with the molecules that make up air, ionize them.
According to more modern concepts, ionization of the atmosphere for the passage of a discharge occurs under the influence of high-energy cosmic radiation - particles with energies of 10 12 -10 15 eV, forming a wide air shower (EAS) with a decrease in the breakdown voltage of the air by an order of magnitude from that under normal conditions.
According to one hypothesis, the particles trigger a process called runaway breakdown. Thus, electron avalanches arise, turning into threads of electrical discharges - streamers, which are highly conductive channels that, merging, give rise to a bright thermally ionized channel with high conductivity - stepped lightning leader.
The movement of the leader to the earth's surface occurs steps several tens of meters at a speed of ~ 50,000 kilometers per second, after which its movement stops for several tens of microseconds, and the glow greatly weakens; then, in the subsequent stage, the leader again advances several tens of meters. A bright glow covers all the steps passed; then a stop and weakening of the glow follows again. These processes are repeated as the leader moves to the surface of the earth at an average speed of 200,000 meters per second.
As the leader moves towards the ground, the field strength at its end increases and, under its action, objects are thrown out from objects protruding on the surface of the Earth. response streamer connecting to the leader. This feature of lightning is used to create a lightning conductor.
In the final stage, the channel ionized by the leader follows back(from bottom to top), or main, lightning discharge, characterized by currents from tens to hundreds of thousands of amperes, brightness, noticeably exceeding the brightness of the leader, and a high speed of advancement, initially reaching up to ~ 100,000 kilometers per second, and at the end decreasing to ~ 10,000 kilometers per second. The channel temperature during the main discharge can exceed 2000-3000 °C. The length of the lightning channel can be from 1 to 10 km, the diameter can be several centimeters. After the passage of the current pulse, the ionization of the channel and its glow weaken. In the final stage, the lightning current can last hundredths and even tenths of a second, reaching hundreds and thousands of amperes. Such lightning is called prolonged lightning and most often causes fires. But the ground is not charged, so it is generally accepted that a lightning discharge occurs from the cloud towards the ground (from top to bottom).
The main discharge often discharges only part of the cloud. Charges located at high altitudes can give rise to a new (swept) leader moving continuously at speeds of thousands of kilometers per second. The brightness of its glow is close to the brightness of the stepped leader. When the swept leader reaches the surface of the earth, a second main blow follows, similar to the first. Typically, lightning includes several repeated discharges, but their number can reach several dozen. The duration of multiple lightning can exceed 1 second. The displacement of the channel of multiple lightning by the wind creates the so-called ribbon lightning - a luminous strip.
Intracloud lightning
Intracloud lightning over Toulouse, France. 2006
Intracloud lightning usually includes only leader stages; their length ranges from 1 to 150 km. The proportion of intracloud lightning increases as it moves toward the equator, changing from 0.5 in temperate latitudes to 0.9 in the equatorial zone. The passage of lightning is accompanied by changes in electric and magnetic fields and radio emissions, the so-called atmospherics.
Flight from Kolkata to Mumbai.
The probability of a ground object being struck by lightning increases as its height increases and with an increase in the electrical conductivity of the soil on the surface or at some depth (the action of a lightning rod is based on these factors). If there is an electric field in the cloud that is sufficient to maintain a discharge, but not sufficient to cause it to occur, a long metal cable or an airplane can act as the lightning initiator - especially if it is highly electrically charged. In this way, lightning is sometimes “provoked” in nimbostratus and powerful cumulus clouds.
Lightning in the upper atmosphere
In 1989, a special type of lightning was discovered - elves, lightning in the upper atmosphere. In 1995, another type of lightning in the upper atmosphere was discovered - jets.
Elves
Jets
Jets are cone tubes blue. The height of the jets can reach 40-70 km (the lower limit of the ionosphere); jets live relatively longer than elves.
Sprites
Sprites difficult to distinguish, but they appear in almost any thunderstorm at an altitude of 55 to 130 kilometers (the altitude of formation of “ordinary” lightning is no more than 16 kilometers). This is a kind of lightning striking upward from a cloud. This phenomenon was first recorded in 1989 by accident. Currently, very little is known about the physical nature of sprites.
Interaction of lightning with the surface of the earth and objects located on it
Global lightning strike frequency (scale shows number of strikes per year per square kilometer)
Early estimates put the frequency of lightning strikes on Earth at 100 times per second. Current data from satellites, which can detect lightning in areas where there is no ground observation, puts the frequency at an average of 44 ± 5 times per second, which equates to approximately 1.4 billion lightning strikes per year. 75% of this lightning strikes between or within clouds, and 25% strikes the ground.
The most powerful lightning strikes cause the birth of fulgurites.
Shock wave from lightning
A lightning discharge is an electrical explosion and is similar in some aspects to detonation. It causes a shock wave that is dangerous in the immediate vicinity. A shock wave from a sufficiently powerful lightning discharge at distances of up to several meters can cause destruction, break trees, injure and concuss people even without direct electric shock. For example, with a current rise rate of 30 thousand amperes per 0.1 millisecond and a channel diameter of 10 cm, the following shock wave pressures can be observed:
- at a distance from the center of 5 cm (border of the luminous lightning channel) - 0.93 MPa,
- at a distance of 0.5 m - 0.025 MPa (destruction of fragile building structures and human injuries),
- at a distance of 5 m - 0.002 MPa (breaking glass and temporarily stunning a person).
At greater distances the shock wave degenerates into sound wave- thunder.
People and lightning
Lightning is a serious threat to human life. A person or animal being struck by lightning often occurs in open spaces, since the electric current travels along the shortest path “thundercloud-ground”. Often lightning strikes trees and transformer installations on the railway, causing them to catch fire. It is impossible to be struck by ordinary linear lightning inside a building, but there is an opinion that so-called ball lightning can penetrate through cracks and open windows. Normal lightning is dangerous for television and radio antennas located on the roofs of high-rise buildings, as well as for network equipment.
The same pathological changes are observed in the body of victims as in case of electric shock. The victim loses consciousness, falls, convulsions may occur, and breathing and heartbeat often stop. It is common to find “current marks” on the body, where electricity enters and exits. In case of death, the cause of cessation of basic vital functions is a sudden stop of breathing and heartbeat, from the direct effect of lightning on the respiratory and vasomotor centers of the medulla oblongata. So-called lightning marks, tree-like light pink or red stripes often remain on the skin, disappearing when pressed with fingers (they persist for 1 - 2 days after death). They are the result of the expansion of capillaries in the area of lightning contact with the body.
Lightning travels through a tree trunk along the path of least electrical resistance, releasing a large amount of heat, turning water into steam, which splits the tree trunk or, more often, tears off sections of bark from it, showing the lightning path. In subsequent seasons, the trees usually repair the damaged tissue and may close the entire wound, leaving only a vertical scar. If the damage is too severe, wind and pests will eventually kill the tree. Trees are natural lightning rods, and are known to provide protection from lightning strikes to nearby buildings. When planted near a building, tall trees catch lightning, and the high biomass of the root system helps ground the lightning strike.
For this reason, you should not hide from the rain under trees during a thunderstorm, especially under tall or solitary trees in open areas.
Musical instruments are made from trees struck by lightning, attributing unique properties to them.
Lightning and electrical installations
Lightning strikes pose a major hazard to electrical and electronic equipment. When lightning directly hits the wires in the line, an overvoltage occurs, causing destruction of the insulation of electrical equipment, and large currents cause thermal damage to the conductors. To protect against lightning surges, electrical substations and distribution networks are equipped with various types protective equipment such as arresters, non-linear surge arresters, long-spark arresters. To protect against direct lightning strikes, lightning rods and lightning protection cables are used. Electromagnetic pulses created by lightning are also dangerous for electronic devices.
Lightning and aviation
Atmospheric electricity in general and lightning in particular pose a significant threat to aviation. A lightning strike on an aircraft causes a large current to spread through its structural elements, which can cause their destruction, fire in fuel tanks, equipment failures, and loss of life. To reduce risk, the metal elements of the outer skin of aircraft are carefully electrically connected to each other, and non-metallic elements are metallized. This ensures low electrical resistance of the housing. To drain lightning current and other atmospheric electricity from the body, aircraft are equipped with arresters.
Due to the fact that the electrical capacity of an aircraft in the air is small, the “cloud-to-aircraft” discharge has significantly less energy compared to the “cloud-to-ground” discharge. Lightning is most dangerous for a low-flying airplane or helicopter, since in this case the aircraft can play the role of a conductor of lightning current from the cloud to the ground. It is known that aircraft at high altitudes are relatively often struck by lightning, and yet, cases of accidents for this reason are rare. At the same time, there are many known cases of aircraft being struck by lightning during takeoff and landing, as well as while parked, which resulted in disasters or destruction of the aircraft.
Lightning and surface ships
Lightning also poses a very big threat to surface ships due to the fact that the latter are elevated above the sea surface and have many sharp elements (masts, antennas) that are concentrators of electric field strength. In the days of wooden sailing ships with a high specific resistance of the hull, a lightning strike almost always ended tragically for the ship: the ship burned down or was destroyed, and people died from electric shock. Riveted steel ships were also vulnerable to lightning. The high resistivity of the rivet seams caused significant local heat generation, which led to the occurrence of an electric arc, fires, destruction of the rivets and the appearance of water leakage in the body.
The welded hull of modern ships has low resistivity and ensures safe spreading of lightning current. The protruding elements of the superstructure of modern ships are reliably electrically connected to the hull and also ensure the safe spread of lightning current.
Human activities that cause lightning
During a ground-based nuclear explosion, a fraction of a second before the arrival of the boundary of the fiery hemisphere, several hundred meters (~400-700 m when compared with an explosion of 10.4 Mt) from the center, the gamma radiation that reaches it produces an electromagnetic pulse with a intensity of ~100-1000 kV/ m, causing lightning discharges striking from the ground upward before the arrival of the border of the fiery hemisphere.
See also
| lightning in Wiktionary | |
| Category:Lightning on Wikimedia Commons |
Notes
- Ermakov V.I., Stozhkov Yu.I. Physics of thunderclouds // Physical Institute named after. P.N. Lebedeva, RAS, M. 2004: 37
- Cosmic rays blamed for lightning Lenta.Ru, 09.02.2009
- Red Elves and Blue Jets
- ELVES, a primer: Ionospheric Heating By the Electromagnetic Pulses from Lightning
- Fractal Models of Blue Jets, Blue Starters Show Similarity, Differences to Red Sprites
- V.P. Pasko, M.A. Stanley, J.D. Matthews, U.S. Inan, and T.G. Wood (March 14, 2002) "Electrical discharge from a thundercloud top to the lower ionosphere," Nature, vol. 416, pages 152-154.
- The appearance of UFOs was explained by sprites. lenta.ru (24.02.2009). Archived from the original on August 23, 2011. Retrieved January 16, 2010.
- John E. Oliver Encyclopedia of World Climatology. - National Oceanic and Atmospheric Administration, 2005. - ISBN 978-1-4020-3264-6
- . National Oceanic and Atmospheric Administration. Archived
- . NASA Science. Science News. (December 5, 2001). Archived from the original on August 23, 2011. Retrieved April 15, 2011.
- K. BOGDANOV “LIGHTNING: MORE QUESTIONS THAN ANSWERS.” “Science and Life” No. 2, 2007
- Zhivlyuk Yu.N., Mandelstam S.L. On the temperature of lightning and the force of thunder // JETP. 1961. T. 40, issue. 2. pp. 483-487.
- N. A. Kun “Legends and Myths” Ancient Greece» LLC "AST Publishing House" 2005-538, p. ISBN 5-17-005305-3 Pages 35-36.
