The nature and causes of lightning

A thunderstorm is a complex atmospheric process, and its occurrence is due to the formation of cumulonimbus clouds. Strong cloudiness is a consequence of the significant instability of the atmosphere. Thunderstorms are characterized by strong winds, often heavy rain (snow), sometimes with hail. Before a thunderstorm (an hour or two before a thunderstorm), atmospheric pressure begins to drop rapidly until the wind suddenly picks up, and then begins to rise.

Thunderstorms can be divided into local, frontal, night, in the mountains. Most often, a person encounters local or thermal thunderstorms. These thunderstorms occur only in hot weather with high atmospheric humidity. As a rule, they occur in the summer at noon or afternoon (12-16 hours). The water vapor in the ascending stream of warm air condenses at a height, while a lot of heat is released and the ascending air streams are heated. The rising air is warmer than the surrounding air and expands until it becomes a thundercloud. Large storm clouds are constantly filled with ice crystals and water droplets. As a result of their crushing and friction between themselves and against the air, positive and negative charges are formed, under the influence of which a strong electrostatic field arises (the strength of the electrostatic field can reach 100,000 V / m). And the potential difference between the individual parts of the cloud, the clouds or the cloud and the earth reaches enormous values. When the critical tension of the electric air is reached, an avalanche-like air ionization occurs - a spark discharge of lightning.

A frontal thunderstorm occurs when masses of cold air enter an area dominated by warm weather. Cold air displaces warm air, while the latter rises to a height of 5-7 km. Warm layers of air invade inside vortices of various directions, a squall is formed, strong friction between the layers of air, which contributes to the accumulation of electric charges. The length of a frontal thunderstorm can reach 100 km. Unlike local thunderstorms, it usually gets colder after frontal thunderstorms. A night thunderstorm is associated with the cooling of the earth at night and the formation of eddy currents of the ascending air. The thunderstorm in the mountains is explained by the difference in solar radiation to which the southern and northern slopes of the mountains are exposed. Night and mountain thunderstorms are not strong and short.

Thunderstorm activity in different regions of our planet is different. World centers of thunderstorms: Java Island - 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.

By type of lightning are divided into linear, pearl and ball. Pearl and ball lightning is quite rare.

The lightning discharge develops in a few thousandths of a second; at such high currents, the air in the zone of the lightning channel almost instantly heats up to a temperature of 30,000-33,000 ° C. As a result, the pressure rises sharply, the air expands - a shock wave occurs, accompanied by a sound impulse - thunder. Due to the fact that on high pointed objects the electric field strength created by the static electric charge of the cloud is especially high, a glow occurs; as a result, air ionization begins, a glow discharge occurs and reddish glow tongues appear, sometimes shortening and again lengthening. Do not attempt to extinguish these fires, as there is no combustion. At a high electric field strength, a beam of luminous filaments may appear - a corona discharge, which is accompanied by a hiss. Linear lightning can also occasionally occur in the absence of thunderclouds. It is no coincidence that the saying arose - "thunder from a clear sky."

Lightning - gas discharge in natural conditions

Introduction3

1.Historical views on lightning 4

2. Lightning 6

Types of lightning9

Physics of linear lightning9

Riddle of ball lightning ……………………………………………...13

3. Ranks 26

Types of discharges26

spark discharge2 6

4. Lightning protection 33

Conclusion3 7

List of usesovannoyliterature39

Introduction

The choice of the topic of my essay is due not only to personal interest, but also to relevance. The nature of lightning is fraught with many mysteries. When describing this rare phenomenon, scientists are forced to rely only on scattered eyewitness accounts. These meager stories, and a handful of photographs - that's all that science has. As one scientist stated, we know no more about lightning than the ancient Egyptians knew about the nature of stars.

Lightning is of great interest not only as a peculiar phenomenon of nature. It makes it possible to observe an electric discharge in a gaseous medium at a voltage of several hundred million volts and a distance between the electrodes of several kilometers. The purpose of this essay is to consider the causes of lightning, the study of various types of electric charges. The issue of lightning protection is also considered in the abstract. People have long understood the harm that a lightning strike can bring, and have come up with protection from it.

Lightning has long been of interest to scientists, but in our time we know only a little more about their nature than 250 years ago, although we were able to detect them even on other planets.

2. Historical views on lightning

Lightning and thunder were originally perceived by people as an expression of the will of the gods and, in particular, as a manifestation of God's wrath. At the same time, the inquisitive human mind has long tried to comprehend the nature of lightning and thunder, to understand their natural causes. In ancient times, Aristotle thought about this. Lucretius thought about the nature of lightning. His attempts to explain the thunder as a consequence of the fact that "the clouds collide there under the pressure of the winds" seem very naive.

For many centuries, including the Middle Ages, it was believed that lightning is a fiery vapor trapped in the water vapor of clouds. Expanding, it breaks through them in the weakest place and quickly rushes down to the surface of the earth.

In 1752, Benjamin Franklin (Fig. 1) experimentally proved that lightning is a strong electrical discharge. The scientist performed the famous experiment with a kite, which was launched into the air when a thunderstorm approached.

Experiment: A pointed wire was fastened to the cross of the snake, a key and a silk ribbon were tied to the end of the rope, which he held with his hand. As soon as the thundercloud was above the kite, the pointed wire began to extract an electric charge from it, and the kite, along with the towline, became electrified. After the rain wets the kite and string, thus making them free to conduct an electric charge, one can observe how the electric charge will "drain" when the finger approaches.

Simultaneously with Franklin, M.V. Lomonosov and G.V. Richman.

Thanks to their research in the middle of the 18th century, the electrical nature of lightning was proved. Since that time, it has become clear that lightning is a powerful electrical discharge that occurs when the clouds are sufficiently electrified.

Lightning

Lightning is an eternal source of recharging the Earth's electric field. At the beginning of the 20th century, atmospheric probes were used to measure the electric field of the Earth. Its strength at the surface turned out to be about 100 V/m, which corresponds to the total charge of the planet about 400,000 C. Ions serve as charge carriers in the Earth's atmosphere, the concentration of which increases with height and reaches a maximum at an altitude of 50 km, where an electrically conductive layer, the ionosphere, was formed under the action of cosmic radiation. Therefore, the electric field of the Earth is the field of a spherical capacitor with an applied voltage of about 400 kV. Under the action of this voltage, a current of 2-4 kA flows from the upper layers to the lower ones, the density of which is 1-12 A/m2, and energy up to 1.5 GW is released. And this electric field would disappear if there were no lightning! Therefore, in good weather, the electric capacitor - Earth - is discharged, and during a thunderstorm it is charged.

Lightning is a natural discharge of large accumulations of electric charge in the lower atmosphere. One of the first to establish this was the American statesman and scientist B. Franklin. In 1752, he experimented with a kite, to the cord of which a metal key was attached, and received sparks from the key during a thunderstorm. Since then, lightning has been intensively studied as an interesting natural phenomenon, and also because of the severe damage to power lines, houses and other structures caused by direct lightning strikes or induced voltages.

How to trigger a lightning bolt? It is very difficult to study what will happen in an incomprehensible place and when. Namely, this is how scientists studying the nature of lightning have worked for many years. It is believed that the storm in the sky is led by Elijah the prophet and we are not given to know his plans. However, scientists have long tried to replace Elijah the prophet by creating a conductive channel between a thundercloud and the earth. For this, B. Franklin launched a kite during a thunderstorm, ending in a wire and a bunch of metal keys. By doing this, he caused weak discharges flowing down the wire, and was the first to prove that lightning is a negative electrical discharge flowing from clouds to the ground. Franklin's experiments were extremely dangerous, and one of those who tried to repeat them, the Russian academician G. V. Richman, died in 1753 from a lightning strike.

In the 1990s, researchers learned how to summon lightning without endangering their lives. One way to cause lightning is to launch a small rocket from the ground directly into a thundercloud. Along the entire trajectory, the rocket ionizes the air and thus creates a conductive channel between the cloud and the ground. And if the negative charge of the bottom of the cloud is large enough, then a lightning discharge occurs along the created channel, all parameters of which are recorded by devices located near the rocket launch pad. To create even better conditions for a lightning discharge, a metal wire is attached to the rocket, connecting it to the ground.

The cloud is a factory for the production of electric charges. However, different "charged" dust can appear on the bodies, even if they are made of the same material - it is enough that the surface microstructure is different. For example, when a smooth body rubs against a rough one, both will be electrified.

A thundercloud is a huge amount of steam, some of which has condensed into tiny droplets or ice floes. The top of a thundercloud can be at a height of 6-7 km, and the bottom hangs above the ground at a height of 0.5-1 km. Above 3-4 km, the clouds consist of ice floes of different sizes, since the temperature there is always below zero. These ice floes are in constant motion, caused by ascending currents of warm air from the heated surface of the earth. Small pieces of ice are easier than large ones to be carried away by ascending air currents. Therefore, "nimble" small ice floes, moving to the upper part of the cloud, all the time collide with large ones. With each such collision, electrification occurs, in which large pieces of ice are charged negatively, and small ones are positively charged. Over time, positively charged small pieces of ice are at the top of the cloud, and negatively charged large ones at the bottom. In other words, the top of a thunderstorm is positively charged, while the bottom is negatively charged. Everything is ready for a lightning discharge, in which a breakdown of air occurs and a negative charge from the bottom of the thundercloud flows to the Earth.

Lightning is a "hello" from space and a source of x-rays. However, the cloud itself is not able to electrify itself so as to cause a discharge between its lower part and the earth. The electric field strength in a thundercloud never exceeds 400 kV/m, and electrical breakdown in air occurs at a strength greater than 2500 kV/m. Therefore, for lightning to occur, something else is needed besides an electric field. In 1992, the Russian scientist A. Gurevich from the Physical Institute. P. N. Lebedeva of the Russian Academy of Sciences (FIAN) suggested that cosmic rays, high-energy particles that fall on the Earth from space at near-light speeds, can be a kind of ignition for lightning. Thousands of such particles bombard every square meter of the earth's atmosphere every second.

According to Gurevich's theory, a particle of cosmic radiation, colliding with an air molecule, ionizes it, resulting in the formation of a huge number of high-energy electrons. Once in the electric field between the cloud and the earth, the electrons are accelerated to near-light speeds, ionizing the path of their movement and, thus, causing an avalanche of electrons moving with them to the earth. The ionized channel created by this avalanche of electrons is used by lightning to discharge.

Recent studies have shown that lightning is a fairly powerful source of x-rays, the intensity of which can be up to 250,000 electron volts, which is about twice that used in chest x-rays.

Types of lightning

a) Most lightning occurs between clouds and the ground, however, there are lightnings that occur between clouds. All these lightnings are called linear. The length of an individual linear lightning can be measured in kilometers.

b) Another type of lightning is tape lightning (Fig. 2). In this case, the following picture, as if there were several almost identical linear lightning shifted relative to each other.

c) It was noticed that in some cases the flash of lightning breaks up into separate luminous sections several tens of meters long. This phenomenon is called bead lightning. According to Malan (1961), this type of lightning is explained on the basis of a protracted discharge, after which the glow would seem to be brighter in the place where the channel bends in the direction of the observer, observing it with its end towards itself. And Youman (1962) believed that this phenomenon should be considered as an example of the "ping effect", which consists in a periodic change in the radius of the discharge column with a period of several microseconds.

d) Ball lightning, which is the most mysterious natural phenomenon.

Physics of linear lightning

Linear lightning is a series of pulses rapidly following each other. Each impulse is a breakdown of the air gap between the cloud and the ground, which occurs in the form of a spark discharge. Let's look at the first impulse first. There are two stages in its development: first, a discharge channel is formed between the cloud and the ground, and then a main current pulse quickly passes through the formed channel.

The first stage is the formation of a discharge channel. It all starts with the fact that an electric field of very high intensity is formed in the lower part of the cloud - 105 ... 106 V / m.

Free electrons receive huge accelerations in such a field. These accelerations are directed downwards, since the lower part of the cloud is negatively charged, while the surface of the earth is positively charged. On the way from the first collision to the next, the electrons acquire significant kinetic energy. Therefore, colliding with atoms or molecules, they ionize them. As a result, new (secondary) electrons are born, which, in turn, are accelerated in the cloud field and then ionize new atoms and molecules in collisions. Entire avalanches of fast electrons arise, forming clouds at the very "bottom", plasma "threads" - a streamer.

Merging with each other, the streamers give rise to a plasma channel, through which the main current pulse subsequently passes.

This plasma channel, which develops from the "bottom" of the cloud to the surface of the earth, is filled with free electrons and ions, and therefore can conduct electric current well. He is called leader or more precisely step leader. The fact is that the channel is not formed smoothly, but in jumps - “steps”.

Why there are pauses in the leader's movement and, moreover, relatively regular ones, is not exactly known. There are several theories of step leaders.

In 1938 Schonlund put forward two possible explanations for the delay that causes the stepping nature of the leader. According to one of them, there should be a movement of electrons down the channel lead streamer (drankaboutthat). However, some of the electrons are captured by atoms and positively charged ions, so that it takes some time for new advancing electrons to enter before a potential gradient is created sufficient for the current to continue. According to another point of view, it takes time for positively charged ions to accumulate under the head of the leader channel and thus create a sufficient potential gradient across it. But the physical processes occurring near the head of the leader are quite understandable. The field strength under the cloud is quite large - it is<
b/m; in the region of space directly in front of the leader's head, it is even greater. In a strong electric field near the leader head, intense ionization of air atoms and molecules occurs. It occurs due, firstly, to the bombardment of atoms and molecules by fast electrons emitted from the leader (the so-called impact ionization), and, secondly, the absorption by atoms and molecules of photons of ultraviolet radiation emitted by the leader (photoionization). Due to the intense ionization of the air atoms and molecules encountered on the leader's path, the plasma channel grows, and the leader moves towards the earth's surface.>

Taking into account the stops along the way, it took the leader 10…20 ms to reach the ground at a distance of 1 km between the cloud and the ground surface. Now the cloud is connected to the ground by a plasma channel, which perfectly conducts current. The channel of ionized gas, as it were, short-circuited the cloud with the earth. This completes the first stage of development of the initial impulse.

Second stage runs fast and powerful. The main current rushes along the path laid by the leader. The current pulse lasts approximately 0.1ms. The current strength reaches values ​​of the order<
A. A significant amount of energy is released (up to
J). The gas temperature in the channel reaches
. It is at this moment that the extraordinarily bright light that we observe in a lightning discharge is born, and thunder occurs, caused by the sudden expansion of a suddenly heated gas.>

It is essential that both the glow and the heating of the plasma channel develop in the direction from the ground to the cloud, i.e. upwards. To explain this phenomenon, we conditionally divide the entire channel into several parts. As soon as the channel is formed (the head of the leader has reached the ground), first of all, the electrons that were in its lowest part jump down; therefore, the lower part of the channel is the first to glow and warm up. Then electrons from the next (higher up part of the channel) rush to the ground; the glow and heating of this part begin. And so gradually - from the bottom to the top - more and more electrons are included in the movement to the ground; as a result, the glow and heating of the channel propagate in the upward direction.

After the main current pulse has passed, there is a pause

duration from 10 to 50ms. During this time, the channel practically goes out, its temperature drops to approximately<
, the degree of channel ionization decreases significantly.>

If more time than usual passes between subsequent lightning strikes, the degree of ionization can be so low, especially in the lower part of the channel, that a new pilot is needed to re-ionize the air. This explains individual cases of the formation of steps at the lower ends of the leaders, preceding not the first but subsequent main lightning strikes.

As discussed above, the new leader follows the path that was blazed by the original leader. It runs all the way from top to bottom without stopping (1ms). And again follows a powerful pulse of the main current. After another pause, everything repeats. As a result, several powerful pulses are emitted, which we naturally perceive as a single lightning discharge, as a single bright flash (Fig. 3).

Ball Lightning Mystery

Ball lightning is absolutely different from ordinary (linear) lightning, neither in its appearance nor in the way it behaves. Ordinary lightning is short-lived; ball lives tens of seconds, minutes. Ordinary lightning is accompanied by thunder; ball is almost silent, its behavior has a lot of unpredictability (Fig. 4).

Ball lightning asks us a lot of mysteries, questions to which there is no clear answer. At present, one can only speculate and make hypotheses.

The only method for studying ball lightning is the systematization and analysis of random observations.

Observation Processing Results

Here is the most reliable information about ball lightning (BL)

CMM is a spherical object with a diameter of 5 ... 30 cm. The shape of the CMM changes slightly, taking pear-shaped or flattened spherical outlines. Very rarely, BL was observed in the form of a torus.

CMM glows usually orange, cases of violet color are noted. The brightness and nature of the glow are similar to the glow of red-hot charcoal, sometimes the intensity of the glow is compared with a weak electric light bulb. Against the background of homogeneous radiation, more brightly luminous regions (glare) appear and move.

The lifetime of BL is from a few seconds to ten minutes. The existence of CMM ends with its disappearance, sometimes accompanied by an explosion or a bright flash that can cause a fire.

CMM is usually observed during a thunderstorm with rain, but there is anecdotal evidence of the observation of CMM during a thunderstorm without rain. There have been cases of observations of CMM over water bodies at a considerable distance from the coast or any objects.

CMM floats in the air and moves along with air currents, but at the same time it can make “strange” active movements that clearly do not coincide with the movement of air.

When colliding with surrounding objects, the BL bounces off like a poorly inflated balloon or ends its existence.

Upon contact with steel objects, the CMM is destroyed, and a bright flash lasting several seconds is observed, accompanied by flying luminous fragments resembling metal welding. Steel objects upon subsequent inspection are slightly melted.

CMM sometimes enters the premises through closed windows. Most of the witnesses describe the process of penetration as pouring through a small hole, a very small part of the witnesses claim that CMM penetrates through intact window glass, while practically not changing its shape.

With a brief touch of the CMM on human skin, minor burns are recorded. Severe burns and even death were recorded at contacts that ended in a flash or explosion.

Significant changes in the size of the BL and the brightness of the glow during the observation period are not observed.

There is evidence of observation of the process of the emergence of CMM from electrical outlets or operating electrical appliances. In this case, a luminous point first appears, which within a few seconds increases to a size of about 10 cm. In all such cases, the BL exists for several seconds and is destroyed with a characteristic pop without significant harm to the objects present and surroundings.

The channel heats up to nearly 30,000 degrees Celsius, five times the temperature of the Sun, producing a bright light (the flash typically lasts only three-quarters of a second). After the formation of the channel, the thundercloud begins to discharge: the first discharge is followed by two, three, four or more sparks.

A lightning strike resembles an explosion and causes the formation of a shock wave, which is extremely dangerous for any living creature that finds itself near the channel. The shock wave of the strongest electric discharge a few meters away from itself is quite capable of breaking trees, injuring or concussing even without a direct electric shock:

• At a distance of up to 0.5 m to the channel, lightning can destroy weak structures and injure a person;
• At a distance of up to 5 meters, the buildings remain intact, but can knock out windows and stun a person;
• At long distances, the shock wave does not carry negative consequences and turns into a sound wave, known as thunder peals.

Thunder rolls

A few seconds after a lightning strike was recorded, due to a sharp increase in pressure along the channel, the atmosphere heats up to 30 thousand degrees Celsius. As a result of this, explosive vibrations of the air arise and thunder occurs. Thunder and lightning are closely interconnected with each other: the length of the discharge is often about eight kilometers, so the sound from different parts of it reaches at different times, forming thunder peals.

Interestingly, by measuring the time that has passed between thunder and lightning, you can find out how far the epicenter of the thunderstorm is from the observer.

To do this, you need to multiply the time between lightning and thunder by the speed of sound, which is from 300 to 360 m / s (for example, if the time interval is two seconds, the epicenter of the thunderstorm is a little more than 600 meters from the observer, and if three - at a distance kilometers). This will help determine if the storm is moving away or approaching.

Amazing fireball

One of the least studied, and therefore the most mysterious phenomena of nature, is ball lightning - a luminous plasma ball moving through the air. It is mysterious because the principle of the formation of ball lightning is still unknown: despite the fact that there are a large number of hypotheses explaining the reasons for the appearance of this amazing natural phenomenon, there were objections to each of them. Scientists have not been able to experimentally achieve the formation of ball lightning.

Spherical lightning is able to exist for a long time and move along an unpredictable trajectory. For example, it is quite capable of hanging in the air for several seconds, and then rushing to the side.

Unlike a simple discharge, there is always one plasma ball: until two or more fire lightnings were simultaneously recorded. The size of ball lightning varies from 10 to 20 cm. Ball lightning is characterized by white, orange or blue tones, although other colors are often found, up to black.

Scientists have not yet determined the temperature indicators of ball lightning: despite the fact that, according to their calculations, it should fluctuate from one hundred to a thousand degrees Celsius, people who were close to this phenomenon did not feel the warmth emanating from ball lightning.

The main difficulty in studying this phenomenon is that scientists rarely manage to fix its appearance, and the testimony of eyewitnesses often casts doubt on the fact that the phenomenon they observed was really ball lightning. First of all, testimony differs as to the conditions in which it appeared: basically it was seen during a thunderstorm.

There are also indications that ball lightning can also appear on a fine day: descend from the clouds, appear in the air, or appear due to some object (tree or pole).

Another characteristic feature of ball lightning is its penetration into closed rooms, it has even been seen in cockpits (a fireball can penetrate windows, descend through ventilation ducts, and even fly out of sockets or a TV). Situations were also repeatedly documented when the plasma ball was fixed in one place and constantly appeared there.

Often, the appearance of ball lightning does not cause trouble (it moves quietly in air currents and flies away or disappears after a while). But, the sad consequences were also noticed when it exploded, instantly evaporating the nearby liquid, melting glass and metal.

Possible dangers

Since the appearance of ball lightning is always unexpected, when you see this unique phenomenon near you, the main thing is not to panic, do not move sharply and do not run anywhere: fire lightning is very susceptible to air vibrations. It is necessary to quietly leave the trajectory of the ball and try to stay as far away from it as possible. If a person is indoors, you need to slowly walk to the window opening and open the window: there are many stories when a dangerous ball left the apartment.

Nothing can be thrown into a plasma ball: it is quite capable of exploding, and this is fraught not only with burns or loss of consciousness, but with cardiac arrest. If it happened that the electric ball caught a person, you need to transfer him to a ventilated room, wrap him up warmer, do a heart massage, artificial respiration and immediately call a doctor.

What to do in a thunderstorm

When a thunderstorm starts and you see lightning approaching, you need to find shelter and hide from the weather: a lightning strike is often fatal, and if people survive, they often remain disabled.

If there are no buildings nearby, and a person is in the field at that time, he must take into account that it is better to hide from a thunderstorm in a cave. But it is advisable to avoid tall trees: lightning usually aims at the largest plant, and if the trees are of the same height, it falls into something that conducts electricity better.

To protect a detached building or structure from lightning, they usually install a high mast near them, on top of which a pointed metal rod is fixed, securely connected to a thick wire, at the other end there is a metal object buried deep in the ground. The operation scheme is simple: a rod from a thundercloud is always charged with a charge opposite to the cloud, which, flowing down the wire underground, neutralizes the charge of the cloud. This device is called a lightning rod and is installed on all buildings of cities and other human settlements.