The nature of lightning and its types. What is lightning? Lightning in the upper atmosphere

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 belongs to the so-called electrodeless discharges, since they begin (and end) in accumulations of charged particles. This determines their some 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 toward 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 They are blue cone tubes. 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 a 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 overvoltages, electrical substations and distribution networks are equipped with various types of protective equipment such as arresters, nonlinear surge arresters, and 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 leaks 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

Notes

1. Ermakov V.I., Stozhkov Yu.I. Physics of thunderclouds // Physical Institute named after. P.N. Lebedeva, RAS, M. 2004: 37
2. Cosmic rays blamed for lightning Lenta.Ru, 09.02.2009
3. Red Elves and Blue Jets
4. ELVES, a primer: Ionospheric Heating By the Electromagnetic Pulses from Lightning
5. Fractal Models of Blue Jets, Blue Starters Show Similarity, Differences to Red Sprites
6. 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.
7. The appearance of UFOs was explained by sprites. lenta.ru (02/24/2009). Archived from the original on August 23, 2011. Retrieved January 16, 2010.
8. John E. Oliver Encyclopedia of World Climatology. - National Oceanic and Atmospheric Administration, 2005. - ISBN 978-1-4020-3264-6
9. . National Oceanic and Atmospheric Administration. Archived
10. . NASA Science. Science News. (December 5, 2001). Archived from the original on August 23, 2011. Retrieved April 15, 2011.
11. K. BOGDANOV “LIGHTNING: MORE QUESTIONS THAN ANSWERS.” “Science and Life” No. 2, 2007
12. 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.
13. N. A. Kun “Legends and Myths of Ancient Greece” LLC “AST Publishing House” 2005-538, p. ISBN 5-17-005305-3 Pages 35-36.
14. Editors: Mariko Namba Walter,Eva Jane Neumann Fridman Shamanism: an encyclopedia of world beliefs, practices, and culture. - ABC-CLIO, 2004. - T. 2. - P. 442. -

Have you ever wondered why birds sit on high-voltage wires, and a person dies when he touches the wires? Everything is very simple - they sit on a wire, but no current flows through the bird, but if the bird flaps its wing, simultaneously touching two phases, it will die. Usually large birds such as storks, eagles, and falcons die this way.

Likewise, a person can touch a phase and nothing will happen to him if no current flows through him; for this you need to wear rubberized boots and God forbid you touch a wall or metal.

Electric current can kill a person in a split second; it strikes without warning. Lightning strikes the earth one hundred times per second and over eight million times per day. This force of nature is five times hotter than the surface of the sun. The electrical discharge strikes with a force of 300,000 amperes and a million volts in a split second. In our daily lives, we think we can control the electricity that powers our homes, outdoor lights, and now our cars. But electricity in its original form cannot be controlled. And lightning is electricity on a huge scale. And yet lightning remains a big mystery. It can strike unexpectedly and its path can be unpredictable.

Lightning in the sky does no harm, but one in ten lightning strikes the surface of the earth. Lightning is divided into many branches, each of which is capable of striking a person located at the epicenter. When a person is struck by lightning, the current can pass from one person to another if they come into contact.

There is a rule of thirty and thirty: if you see lightning and hear thunder less than thirty seconds later, you must seek shelter, and then you must wait thirty minutes from the last clap of thunder before going outside. But lightning does not always follow a strict order.

There is such an atmospheric phenomenon as thunder from a clear sky. Often lightning, leaving a cloud, travels up to sixteen kilometers before striking the ground. In other words, lightning can appear out of nowhere. Lightning needs wind and water. When strong winds lift moist air, the conditions are created for destructive thunderstorms to occur.

It is impossible to decompose into components something that fits into a millionth of a second. One false belief is that we see lightning as it travels to the ground, but what we actually see is the lightning's return path into the sky. Lightning is not a unidirectional strike to the ground, but is actually a ring, a path in two directions. The flash of lightning that we see is the so-called return stroke, the final phase of the cycle. And when the return stroke of lightning heats up the air, its calling card appears - thunder. The return path of lightning is the part of lightning that we see as a flash and hear as thunder. A reverse current of thousands of amperes and millions of volts rushes from the ground to the cloud.

Lightning regularly electrocutes people indoors. It can enter a structure in different ways, through drainpipes and water pipes. Lightning can penetrate electrical wiring, the current strength of which in an ordinary house does not reach two hundred amperes and overloads the electrical wiring in jumps from twenty thousand to two hundred thousand amperes. Perhaps the most dangerous path in your home leads directly to your hand through the phone. Nearly two-thirds of indoor electric shocks occur when people pick up a landline telephone during a lightning strike. Cordless phones are safer during thunderstorms, but lightning can electrocute someone standing near the phone's base. Even a lightning rod cannot protect you from all lightning, since it is not capable of catching lightning in the sky.

About the nature of lightning

There are several different theories explaining the origin of lightning.

Typically, the lower part of the cloud carries a negative charge, and the upper part carries a positive charge, making the cloud-earth system like a giant capacitor.

When the electrical potential difference becomes large enough, a discharge known as lightning occurs between the ground and the cloud, or between two parts of the cloud.

Is it dangerous to be in a car during lightning?

In one of these experiments, a meter-long artificial lethal lightning was directed at the steel roof of a car in which a person was sitting. Lightning passed through the casing without harming a person. How did this happen? Since charges on a charged object repel each other, they tend to move as far apart as possible.

In the case of a hollow mechanical ball pi cylinder, the charges are distributed over the outer surface of the object. Similarly, if lightning strikes the metal roof of a car, then the repelling electrons will spread extremely quickly over the surface of the car and go through its body into the ground. Therefore, lightning along the surface of a metal car goes into the ground and does not get inside the car. For the same reason, a metal cage is perfect protection against lightning. As a result of artificial lightning striking a car with a voltage of 3 million volts, the potential of the car and the body of the person in it increases to almost 200 thousand volts. At the same time, a person does not experience the slightest sign of an electric shock, since there is no potential difference between any points of his body.

This means that staying in a well-grounded building with a metal frame, of which there are many in modern cities, almost completely protects against lightning.

How can we explain that birds sit on the wires completely calmly and with impunity?

The body of a sitting bird is like a branch of a chain (parallel connection). The resistance of this branch with the bird is much greater than the resistance of the wire between the bird's legs. Therefore, the current strength in the bird’s body is negligible. If a bird, sitting on a wire, touched the pole with its wing or tail, or otherwise connected with the ground, it would be instantly killed by the current that would rush through it into the ground.

Interesting facts about lightning

The average length of lightning is 2.5 km. Some discharges extend up to 20 km in the atmosphere.

Lightning is beneficial: they manage to snatch millions of tons of nitrogen from the air, bind it and send it into the ground, fertilizing the soil.

Saturn's lightning is a million times stronger than Earth's.

A lightning discharge usually consists of three or more repeated discharges - pulses following the same path. The intervals between successive pulses are very short, from 1/100 to 1/10 s (this is what causes lightning to flicker).

About 700 lightning flashes on Earth every second. World centers of thunderstorms: the island of Java - 220, equatorial Africa - 150, southern Mexico - 142, Panama - 132, central Brazil - 106 thunderstorm days a year. Russia: Murmansk - 5, Arkhangelsk - 10, St. Petersburg - 15, Moscow - 20 thunderstorm days a year.

The air in the zone of the lightning channel almost instantly heats up to a temperature of 30,000-33,000 ° C. On average, about 3,000 people die from lightning strikes in the world every year

Statistics show that every 5,000-10,000 flight hours there is one lightning strike on an aircraft; fortunately, almost all damaged aircraft continue to fly.

Despite the crushing power of lightning, protecting yourself from it is quite simple. During a thunderstorm, you should immediately leave open areas, under no circumstances should you hide under isolated trees, or be near high masts and power lines. You should not hold steel objects in your hands. Also, during thunderstorms, you cannot use radio communications or mobile phones. Televisions, radios and electrical appliances must be turned off indoors.

Lightning discharges ( lightning) is the most common source of naturally occurring powerful electromagnetic fields. Lightning is a type of gas discharge with a very long spark length. The total length of the lightning channel reaches several kilometers, and a significant part of this channel is located inside a thundercloud. Lightning The cause of lightning is the formation of a large volumetric electric charge.

Ordinary source of lightning are thunderstorm cumulonimbus clouds that carry an accumulation of positive and negative electrical charges in the upper and lower parts of the cloud and form electric fields of increasing intensity around this cloud. The formation of such space charges of different polarities in the cloud (cloud polarization) is associated with condensation due to the cooling of water vapor of rising warm air flows on positive and negative ions (condensation centers) and the separation of charged moisture droplets in the cloud under the influence of intense ascending thermal air flows. Due to the fact that several charge clusters isolated from each other are formed in the cloud (mainly charges of negative polarity accumulate in the lower part of the cloud).

Lightning discharges can be divided into several types based on external signs. Regular type - linear lightning, with varieties: ribbon, rocket, zigzag and branched. The rarest type of discharge is ball lightning. There are known discharges called “St. Elmo’s Fire” and “Glow of the Andes.” Lightning usually occurs multiple times, i.e. consists of several single discharges developing along the same path, and each discharge, just like the discharge obtained in laboratory conditions, begins with a leader and ends with a reverse (main) discharge. The descent speed of the leader of the first single discharge is approximately 1500 km/s, the speed of the leaders of subsequent discharges reaches 2000 km/s, and the speed of the reverse discharge varies within 15000 -150000 km/s, i.e. from 0.05 to 0.5 speed Sveta. The leader channel, like the channel of any streamer, is filled with plasma and therefore has a certain conductivity.

The upper end of the leader channel is connected to one of the charged centers in the cloud, so part of the charges of this center flows into the leader channel. The charge distribution in the channel should be uneven, increasing towards its end. However, some indirect measurements suggest that the absolute value of the charge on the leader head is small and, to a first approximation, the channel can be considered uniformly charged with a linear charge density S. The total charge in the leader channel in this case is equal to Q = S*l, where l is the channel length , and its value is usually about 10% of the value of the charge flowing into the ground during a single lightning discharge. In 70-80% of all cases, this charge has a negative polarity. As the leader channel moves, under the influence of the electric field it creates in the ground, charges shift, and charges opposite in sign to the leader charges (usually positive charges) tend to be located as close as possible to the head of the leader channel. In the case of homogeneous soil, these charges accumulate directly under the leader channel.

If the soil is heterogeneous and its main part has a high resistivity, charges are concentrated in areas with high conductivity (rivers, groundwater). In the presence of grounded, towering objects (lightning rods, chimneys, tall buildings, rain-drenched trees), the charges are drawn to the top of the object, creating significant field strength there. At the first stages of development of the leader channel, the electric field strength at its head is determined by the leader’s own charges and clusters of space charges located under the cloud. The leader's trajectory is not connected with earthly objects. As the leader descends, accumulations of charges on the ground and elevated objects begin to have an increasing influence. Starting from a certain height of the leader's head (orientation height), the field strength in one of the directions turns out to be the greatest, and the leader is oriented towards one of the ground objects. Naturally, in this case, elevated objects and areas of land with increased conductivity are predominantly affected (selective susceptibility). From very high objects, counter leaders develop towards the leader, the presence of which helps to orient the lightning towards a given object.

After the leader channel reaches the ground or the counter leader, the reverse discharge begins, during which the leader channel acquires a potential almost equal to the ground potential. At the head of the upwardly developing reverse discharge there is an area of ​​​​increased electric field strength, under the influence of which a restructuring of the channel occurs, accompanied by an increase in the plasma charge density from 10^13 - 10^14 to 10^16 - 10^19 1/m3, due to which the channel conductivity increases at least 100 times. During the development of a reverse discharge, a current iM = v passes through the impact site, where v is the speed of the reverse discharge. The process that occurs during the transition of the leader discharge to the reverse discharge is in many ways similar to the process of a vertical charged wire shorting to ground.

If a charged wire is connected to ground through a resistance r, then the current at the grounding point is equal to: where z = characteristic impedance of the wire. Thus, even during a lightning discharge, the current at the strike site will be equal to v only if the grounding resistance is zero. When grounding resistances are different from zero, the current at the point of impact decreases. It is quite difficult to quantify this decrease, since the wave impedance of the lightning channel can only be roughly estimated. There is reason to believe that the characteristic impedance of the lightning channel decreases with increasing current, with the average value being approximately 200 - 300 Ohms. In this case, when the grounding resistance of an object changes from 0 to 30 Ohms, the current in the object changes by only 10%. In what follows, we will call such objects well grounded and assume that the full lightning current iM = v passes through them. Basic parameters of lightning and intensity of thunderstorm activity Lightning with high currents occurs extremely rarely. Thus, lightning with currents of 200 kA occurs in 0.7...1.0% of cases of the total number of observed discharges.

The number of cases of lightning strikes with a current value of 20 kA is about 50%. Therefore, it is customary to present the amplitude values ​​of lightning currents in the form of probability curves (distribution functions), for which the probability of the occurrence of lightning currents with the maximum value is plotted along the ordinate axis. The main quantitative characteristic of lightning is the current flowing through the affected object, which is characterized by the maximum value iM, the average steepness of the front and the pulse duration ti, which is equal to the time the current decreases to half the maximum value. Currently, the largest amount of data is available on the maximum values ​​of lightning current, the measurement of which is carried out by the simplest measuring instruments - magnetic recorders, which are cylindrical rods made of steel filings or wires pressed into plastic. Magnetic recorders are mounted near towering objects (lightning rods, transmission line supports) and are located along the magnetic field lines that arise when lightning current passes through the object. Since materials with high coercive force are used for the manufacture of recorders, they retain a large residual magnetization.

By measuring this magnetization, it is possible to determine the maximum value of the magnetizing current using calibration curves. Measurements with magnetic recorders do not provide great accuracy, but this disadvantage is partially compensated by the huge number of measurements, which currently number in the tens of thousands. By placing a frame closed to an inductive coil near the affected object, you can measure the slope of the lightning current using a magnetic recorder placed inside the coil. Measurements have shown that lightning currents vary widely from several kiloamperes to hundreds of kiloamperes, therefore the measurement results are presented in the form of probability curves (distribution functions) of lightning currents, on which the probability of lightning currents with a maximum value exceeding the value indicated is plotted on the abscissa axis. ordinate.

In Ukraine, when calculating lightning protection, the curve is used. For mountainous areas, the ordinates of the curve are reduced by 2 times, since at short distances from the ground to the clouds, lightning occurs at a lower density of charges in clusters, i.e., the probability of large currents decreases. It is much more difficult to experimentally determine the steepness and duration of a lightning current pulse, therefore the amount of experimental data on these parameters is relatively small. The duration of the lightning current pulse is mainly determined by the time of propagation of the reverse discharge from the ground to the cloud and, therefore, varies within a relatively narrow range from 20 to 80-100 μs. The average duration of a lightning current pulse is close to 50 μs, which determined the choice of the standard pulse.

The most important from the point of view of assessing the lightning resistance of RES are: the amount of charge transferred by lightning, the current in the lightning channel, the number of repeated strikes along one channel and the intensity of lightning activity. All these parameters are not determined unambiguously and are probabilistic in nature. The charge transferred by lightning fluctuates during the discharge process in the range from fractions of a coulomb to several tens of coulombs. The average charge dropped into the ground by repeated lightning is 15 - 25 C. Considering that on average a lightning discharge contains three components, therefore, during one component, about 5 - 8 C are transferred to the ground. Of these, about 60% of the entire given accumulation of charges flows into the leader channel, which amounts to 3 - 5 C. A lightning strike into flat areas of the earth's surface carries a charge of 10 - 50 C (on average 25 C), with lightning strikes in the mountains - a charge of 30 - 100 C (on average 60 C), with discharges into television towers the charge reaches 160 C.

When lightning strikes into the ground, the overwhelming majority (85 - 90%) transfer a negative charge to the ground. The charge flowing into the ground during multiple lightning varies from fractions of a coulomb to 100 C or more. The average value of this charge is close to 20 C. The charge released into the ground during thunderstorms appears to play a significant role in maintaining the negative charge of the ground. The intensity of thunderstorm activity in different climatic regions varies greatly. As a rule, the number of thunderstorms throughout the year is minimal in the northern regions and gradually increases to the south, where increased air humidity and high temperatures contribute to the formation of thunderclouds. However, this trend is not always followed. There are centers of thunderstorm activity in mid-latitudes (for example, in the Kyiv region), where favorable conditions are created for the formation of local thunderstorms.

The intensity of thunderstorm activity is usually characterized by the number of thunderstorm days per year or the total annual duration of thunderstorms in hours. The last characteristic is more correct, since the number of lightning strikes into the ground does not depend on the number of thunderstorms, but on their total duration. The number of thunderstorm days or hours per year is determined on the basis of long-term observations of meteorological stations, the generalization of which makes it possible to draw maps of thunderstorm activity, on which lines of equal duration of thunderstorms are plotted - isokeranic lines. The average duration of thunderstorms per thunderstorm day for the territory of the European part of Russia and Ukraine is 1.5-2 hours.

Just recently the clear, clear sky was covered with clouds. The first drops of rain fell. And soon the elements demonstrated their power to the earth. Thunder and lightning pierced the stormy sky. Where do such phenomena come from? For many centuries, humanity has seen in them a manifestation of divine power. Today we know about the occurrence of such phenomena.

Origin of thunderclouds

Clouds appear in the sky from condensation rising high above the ground and float in the sky. The clouds are heavier and larger. They bring with them all the “special effects” that come with bad weather.

Thunderclouds differ from ordinary clouds in that they are charged with electricity. Moreover, there are clouds with a positive charge, and there are clouds with a negative one.

To understand where thunder and lightning come from, you need to rise higher above the ground. In the sky, where there are no obstacles to free flight, the winds blow stronger than on the ground. They are the ones who provoke the charge in the clouds.

The origin of thunder and lightning can be explained by just one drop of water. It has a positive charge of electricity in the center and a negative charge on the outside. The wind breaks it into pieces. One of them remains with a negative charge and has less weight. Heavier positively charged drops form the same clouds.

Rain and electricity

Before thunder and lightning appear in a stormy sky, the wind separates the clouds into positively and negatively charged ones. Rain falling on the ground takes some of this electricity with it. An attraction forms between the cloud and the surface of the earth.

The negative charge of the cloud will attract the positive one on the ground. This attraction will be located evenly on all surfaces that are elevated and conduct current.

And now the rain creates all the conditions for the appearance of thunder and lightning. The higher the object is to the cloud, the easier it is for lightning to break through to it.

Origin of lightning

The weather has prepared all the conditions that will help all its effects appear. She created the clouds from which thunder and lightning come.

A roof charged with negative electricity attracts the positive charge of the most exalted object. Its negative electricity will go into the ground.

Both of these opposites tend to attract each other. The more electricity there is in a cloud, the more it is in the most elevated object.

Accumulating in a cloud, electricity can break through the layer of air located between it and the object, and sparkling lightning will appear and thunder will thunder.

How lightning develops

When a thunderstorm rages, lightning and thunder accompany it incessantly. Most often, the spark comes from a negatively charged cloud. It develops gradually.

First, a small stream of electrons flows from the cloud through a channel directed toward the ground. In this place of the cloud, electrons moving at high speed accumulate. Due to this, electrons collide with air atoms and break them up. Individual nuclei are obtained, as well as electrons. The latter also rush to the ground. While they move along the channel, all primary and secondary electrons again split the air atoms standing in their way into nuclei and electrons.

The whole process is like an avalanche. It is moving upward. The air heats up and its conductivity increases.

More and more electricity from the cloud flows to the ground at a speed of 100 km/s. At this moment, lightning makes its way to the ground. Along this road laid by the leader, electricity begins to flow even faster. A discharge of enormous force occurs. Reaching its peak, the discharge decreases. The channel, heated by such a powerful current, glows. And lightning becomes visible in the sky. Such a discharge does not last long.

After the first discharge, a second one often follows along a laid channel.

How does thunder appear?

Thunder, lightning, and rain are inseparable during a thunderstorm.

Thunder occurs for the following reason. The current in the lightning channel is generated very quickly. The air becomes very hot. This makes it expand.

It happens so quickly that it resembles an explosion. Such a shock shakes the air violently. These vibrations lead to the appearance of a loud sound. This is where lightning and thunder come from.

As soon as the electricity from the cloud reaches the ground and disappears from the channel, it cools very quickly. Compressing air also causes thunder to sound.

The more lightning that passes through the channel (there can be up to 50 of them), the longer the air tremors. This sound is reflected from objects and clouds, and an echo occurs.

Why is there an interval between lightning and thunder?

In a thunderstorm, lightning is followed by thunder. Its delay from lightning occurs due to the different speeds of their movement. Sound moves at a relatively low speed (330 m/s). This is only 1.5 times faster than the movement of a modern Boeing. The speed of light is much greater than the speed of sound.

Thanks to this interval, it is possible to determine how far flashing lightning and thunder are from the observer.

For example, if 5 s passed between lightning and thunder, this means that the sound traveled 330 m 5 times. By multiplying, it is easy to calculate that the lightning from the observer was at a distance of 1650 m. If a thunderstorm passes closer than 3 km from a person, it is considered close. If the distance, in accordance with the appearance of lightning and thunder, is further, then the thunderstorm is distant.

Lightning in numbers

Thunder and lightning have been modified by scientists, and the results of their research are presented to the public.

It has been found that the potential difference preceding lightning reaches billions of volts. The current strength at the moment of discharge reaches 100 thousand A.

The temperature in the channel heats up to 30 thousand degrees and exceeds the temperature on the surface of the Sun. From the clouds to the ground, lightning travels at a speed of 1000 km/s (in 0.002 s).

The internal channel through which the current flows does not exceed 1 cm, although the visible one reaches 1 m.

There are approximately 1,800 thunderstorms occurring continuously around the world. The chance of being killed by lightning is 1:2000000 (the same as dying from falling out of bed). The chance of seeing ball lightning is 1 in 10,000.

Ball lightning

On the path to studying where thunder and lightning come from in nature, the most mysterious phenomenon is ball lightning. These round fiery discharges have not yet been fully studied.

Most often, the shape of such lightning resembles a pear or watermelon. It lasts up to several minutes. Appears at the end of a thunderstorm in the form of red clumps from 10 to 20 cm in diameter. The largest ball lightning ever photographed was about 10 m in diameter. It makes a buzzing, hissing sound.

It may disappear quietly or with a slight crash, leaving a burning smell and smoke.

The movement of lightning does not depend on the wind. They are drawn into closed spaces through windows, doors and even cracks. If they come into contact with a person, they leave severe burns and can be fatal.

Until now, the reasons for the appearance of ball lightning were unknown. However, this is not evidence of its mystical origin. Research is being conducted in this area that can explain the essence of this phenomenon.

By becoming familiar with phenomena such as thunder and lightning, you can understand the mechanism of their occurrence. This is a consistent and rather complex physical and chemical process. It is one of the most interesting natural phenomena that occurs everywhere and therefore affects almost every person on the planet. Scientists have solved the mysteries of almost all types of lightning and even measured them. Ball lightning today is the only unsolved mystery of nature in the field of formation of such natural phenomena.

Origin of thunderclouds

Fog that rises high above the ground consists of water particles and forms clouds. Larger and heavier clouds are called clouds. Some clouds are simple - they do not cause lightning or thunder. Others are called thunderstorms, since they are the ones who create a thunderstorm, form lightning and thunder. Thunderclouds differ from simple rain clouds in that they are charged with electricity: some are positive, others are negative.

How do thunderclouds form? Everyone knows how strong the wind can be during a thunderstorm. But even stronger air vortices form higher above the ground, where forests and mountains do not interfere with air movement. This wind mainly creates positive and negative electricity in the clouds.

At the center of each drop there is positive electricity, and equal negative electricity is located on the surface of the drop. Falling raindrops are picked up by the wind and fall into air currents. The wind hitting the drop with force breaks it into pieces. In this case, the breakaway outer particles of the drop become charged with negative electricity.

The remaining larger and heavier part of the drop is charged with positive electricity. That part of the cloud in which heavy droplet particles accumulate is charged with positive electricity. Rain falling from a cloud carries some of the cloud's electricity to the ground and, thus, an electrical attraction is created between the cloud and the ground.

In Fig. Figure 1 shows the distribution of electricity in a cloud and on the surface of the earth. If a cloud is charged with negative electricity, then, trying to be attracted to it, the positive electricity of the earth will be distributed on the surface of all elevated objects that conduct electric current. The higher the object standing on the ground, the smaller the distance between its top and the bottom of the cloud and the smaller the layer of air remaining here that separates opposite electricity. Obviously, in such places it is easier for lightning to reach the ground. We will talk about this in more detail later.

Rice. 1. Distribution of electricity in a thundercloud and ground objects

Why does lightning happen?

When approaching a tall tree or house, a thundercloud charged with electricity affects it. In Fig. 1 cloud charged with negative electricity attracts positive electricity to the roof, and the negative electricity of the house goes into the ground.

Both electricity - in the cloud and in the roof of the house - tend to attract each other. If there is a lot of electricity in the cloud, then a lot of electricity is generated in the house through the influence.

Just as rising water can wash away a dam and rush in a stormy stream, flooding a valley in its uncontrollable movement, so electricity, accumulating in increasing quantities in a cloud, can eventually break through the layer of air separating it from the surface of the earth and rush down towards the earth, towards the opposite electricity. A strong discharge will occur - an electric spark will jump between the cloud and the house.

This is lightning striking the house. Lightning discharges can occur not only between a cloud and the ground, but also between two clouds charged with different types of electricity.

The stronger the wind, the sooner the cloud becomes charged with electricity. The wind expends a certain amount of work, which goes into separating positive and negative electricity.

How does lightning develop?

Most often, lightning striking the ground comes from clouds charged with negative electricity. Lightning striking from such a cloud develops like this.

First, electrons begin to flow from the cloud towards the ground in small quantities, in a narrow channel, forming something like a stream in the air.

In Fig. Figure 2 shows this beginning of lightning formation. In the part of the cloud where the formation of the channel begins, electrons have accumulated and have a high speed of movement, due to which they, when colliding with air atoms, break them into nuclei and electrons.

Rice. 2. Lightning begins to form in the cloud

The electrons released in this case also rush towards the ground and, again colliding with air atoms, split them. This is similar to the fall of snow in the mountains, when at first a small lump, rolling down, becomes overgrown with snowflakes sticking to it, and, accelerating its run, turns into a formidable avalanche.

And here the electron avalanche captures more and more volumes of air, splitting its atoms into pieces. At the same time, the air heats up, and as the temperature rises, its conductivity increases. It turns from an insulator into a conductor. Through the resulting conductive channel of air, electricity begins to flow out of the cloud in increasing quantities. Electricity is approaching the earth at enormous speeds, reaching 100 kilometers per second.

After hundredths of a second, the electron avalanche reaches the ground. This ends only the first, so to speak, “preparatory” part of the lightning: the lightning has made its way to the ground. The second, main part of the development of lightning is still ahead. The considered part of the lightning formation is called the leader. This foreign word means “leading” in Russian. The leader paved the way for the second, more powerful part of the lightning; this part is called the main part. As soon as the channel reaches the ground, electricity begins to flow through it much more violently and quickly.

Now there is a connection between the negative electricity accumulated in the channel and the positive electricity that entered the ground with raindrops and through electrical influence - a discharge of electricity occurs between the cloud and the ground. Such a discharge represents an electric current of enormous force - this force is much greater than the current in a conventional electrical network.

The current flowing in the channel increases very quickly, and having reached its greatest strength, it begins to gradually decrease. The lightning channel through which such a strong current flows becomes very hot and therefore glows brightly. But the time of current flow in a lightning discharge is very short. The discharge lasts for very small fractions of a second, and therefore the electrical energy that is obtained during the discharge is relatively small.

In Fig. Figure 3 shows the gradual movement of the lightning leader towards the ground (the first three figures on the left).

Rice. 3. Gradual development of the leader of the lightning (the first three pictures) and its main part (the last three pictures).

The last three pictures show individual moments of the formation of the second (main) part of the lightning. A person looking at lightning, of course, will not be able to distinguish its leader from the main part, since they follow each other extremely quickly, along the same path.

After connecting two different types of electricity, the current is interrupted. However, the lightning usually doesn't end there. Often, a new leader immediately rushes along the path laid by the first discharge, and behind him, along the same path, the eye part of the discharge again follows. This completes the second category.

The time between the formation of individual discharges is very short. It does not exceed hundredths of a second. If the number of discharges is very large, then the duration of lightning can reach a whole second or even several seconds.

We looked at only one type of lightning, which is the most common. This lightning is called linear lightning because to the naked eye it appears as a line - a narrow bright stripe of white, light blue or bright pink.

Linear lightning has a length from hundreds of meters to many kilometers. The path of lightning is usually zigzag. Lightning often has many branches. As already mentioned, linear lightning discharges can occur not only between a cloud and the ground, but also between clouds.

Ball lightning

In addition to linear, there are, although much less frequently, lightning of other types. Of these, we will consider one, the most interesting - ball lightning.

Sometimes lightning discharges are observed, which are fireballs. How ball lightning is formed has not yet been studied, but existing observations of this interesting type of lightning discharge allow us to draw some conclusions.

Most often, ball lightning has the shape of a watermelon or pear. It lasts for a relatively long time - from a small fraction of a second to several minutes.

The most common duration of ball lightning is from 3 to 5 seconds. Ball lightning most often appears at the end of a thunderstorm in the form of red luminous balls with a diameter of 10 to 20 centimeters. In more rare cases, it also has larger sizes. For example, a lightning bolt with a diameter of about 10 meters was photographed.

The ball can sometimes be dazzling white and have a very sharp outline. Typically, ball lightning makes a whistling, buzzing or hissing sound.

Ball lightning may disappear quietly, but may also produce a faint crackling sound or even a deafening explosion. When it disappears, it often leaves a pungent-smelling haze. Near the ground or in enclosed spaces, ball lightning moves at the speed of a running person - approximately two meters per second. It can remain at rest for some time, and such a “settled” ball hisses and throws out sparks until it disappears. Sometimes it seems that ball lightning is driven by the wind, but usually its movement does not depend on the wind.

Ball lightning is attracted to enclosed spaces, into which they enter through open windows or doors, and sometimes even through small cracks. The pipes represent a good path for them; Therefore, ball lightning often appears from ovens in kitchens. After circling around the room, ball lightning leaves the room, often leaving along the very path along which it entered.

Sometimes lightning rises and falls two or three times over distances from several centimeters to several meters. Simultaneously with these ascents and descents, the fireball sometimes moves in a horizontal direction, and then it seems that the ball lightning is making leaps.

Often, ball lightning “settles” on conductors, preferring the highest points, or rolls along conductors, for example, along drainpipes. Moving over people's bodies, sometimes under clothes, ball lightning causes severe burns and even death. There are many descriptions of cases of fatal damage to people and animals by ball lightning. Ball lightning can cause very severe damage to buildings.

Where does lightning strike?

Since lightning is an electrical discharge through the thickness of an insulator - air, it occurs most often where the layer of air between the cloud and any object on the surface of the earth is smaller. Direct observations show this: lightning tends to strike high bell towers, masts, trees and other tall objects.

However, lightning does not only rush towards tall objects. From two adjacent masts of the same height, one made of wood and the other of metal, and standing not far from one another, lightning will rush to the metal one. This will happen for two reasons. Firstly, metal conducts electricity much better than wood, even if it is damp. Secondly, the metal mast is well connected to the ground, and electricity from the ground can flow more freely to the mast during the development of the leader.

The latter circumstance is widely used to protect various buildings from lightning strikes. The greater the surface of the metal of the mast in contact with the ground, the easier it is for electricity to pass from the cloud to the ground.

This can be compared to how a stream of liquid pours through a funnel into a bottle. If the hole in the funnel is large enough, the stream will immediately go into the bottle. If the hole in the funnel is small, then the liquid will begin to overflow over the edge of the funnel and spill out onto the floor.

Lightning can also strike a flat surface of the earth, but at the same time it also rushes to where the electrical conductivity of the soil is greater. For example, damp clay or marshy ground is more likely to be struck by lightning than dry sand or rocky, dry soil. For the same reason, lightning strikes the banks of rivers and streams, preferring them to tall but dry trees towering nearby.

This feature of lightning - rushing towards bodies that are well connected to the ground and well conducting - is widely used to implement various protective devices.