Lightning is her nature. Basic knowledge about lightning protection. Lightning rod as the main lightning protection

The clouds spread their wings and blocked the sun from us...

Why do we sometimes hear thunder and see lightning when it rains? Where do these outbreaks come from? Now we will tell you about this in detail.

What is lightning?

What is lightning? This is amazing and very mysterious phenomenon nature. It almost always happens during a thunderstorm. Some are amazed, some are frightened. Poets write about lightning, scientists study this phenomenon. But much remains unsolved.

One thing is certain - it is a giant spark. It's like a billion light bulbs exploded! Its length is enormous - several hundred kilometers! And she is very far from us. That is why we see it first, and only then hear it. Thunder is the “voice” of lightning. After all, light reaches us faster than sound.

And lightning also happens on other planets. For example, on Mars or Venus. Normal lightning lasts only a fraction of a second. It consists of several categories. Lightning sometimes appears quite unexpectedly.

How is lightning formed?

Lightning is usually born in a thundercloud, high above the ground. Thunderclouds appear when the air begins to become very hot. This is why there are amazing thunderstorms after a heat wave. Billions of charged particles literally flock to the place where it originates. And when there are very, very many of them, they burst into flames. That's where lightning comes from - from a thundercloud. She can hit the ground. The earth attracts her. But it can also explode in the cloud itself. It all depends on what kind of lightning it is.

What types of lightning are there?

There are different types of lightning. And you need to know about this. This is not just a “ribbon” in the sky. All these “ribbons” are different from each other.

Lightning is always a strike, it is always a discharge between something. There are more than ten of them! For now, let’s name only the most basic ones, attaching pictures of lightning to them:

• Between a thundercloud and the ground. These are the same “ribbons” that we are used to.

Between a tall tree and a cloud. The same “ribbon”, but the blow is directed in the other direction.

Ribbon zipper - when there is not one “ribbon”, but several in parallel.

• Between cloud and cloud, or simply “played out” in one cloud. This type of lightning can often be seen during a thunderstorm. You just need to be careful.

• There are also horizontal lightning that do not touch the ground at all. They are endowed with colossal strength and are considered the most dangerous

• And everyone has heard about ball lightning! Only a few have seen them. There are even fewer who would like to see them. And there are also people who do not believe in their existence. But ball lightning exists! It is difficult to photograph such lightning. It explodes quickly, although it can “take a walk”, but it’s better for the person next to it not to move - it’s dangerous. So there’s no time for a camera here.

• View of lightning with very beautiful name- "St. Elmo's Fire." But it's not exactly lightning. This is the glow that appears at the end of a thunderstorm on pointed buildings, lanterns, and ship masts. Also a spark, but not fading and not dangerous. St. Elmo's Fire is very beautiful.

• Volcanic lightning occurs when a volcano erupts. The volcano itself already has a charge. This is probably what causes lightning.

• Sprite lightning is something that you cannot see from Earth. They appear above the clouds and few people are studying them yet. These lightning bolts look like jellyfish.

• The dotted lightning has hardly been studied. It can be seen extremely rarely. Visually, it really looks like a dotted line - as if a lightning ribbon is melting.

These are the different kinds of lightning. There is only one law for them - electric discharge.

Conclusion.

Even in ancient times, lightning was considered both a sign and the wrath of the Gods. She was a mystery before and remains one now. No matter how they break it down into the smallest atoms and molecules! And it’s always incredibly beautiful!

These short articles are for those who are familiar with at least a school physics course, work in technology or construction, but have never encountered the problem of lightning protection before. Our reader should understand that after getting acquainted with these pages, he will not design lightning protection and will not avoid contacting specialists, but he will be able to formulate his task to them and distinguish proposals for truly important technical measures from thoughtful delusions aimed at increasing the volume of work and pumping out money.
The given numerical estimates are deliberately simplified to the limit. Four operations of arithmetic is all that is used in them. In any case, the result and purpose of the assessment was not a strict number, but an understanding of the essence physical phenomenon and its significance for lightning protection.
We are glad to see your questions and comments. They will not be ignored and will be used to further correct the text. We hope that the educational program that was started on this site will ultimately be almost equally useful to both readers and compilers.

This question is asked to specialists almost more often than others. The answer seems simple. Everyone knows that lightning is a giant electrical discharge in an electric field. thundercloud. As it moves toward the ground, the lightning channel creates a highly conductive plasma from non-conducting air. This occurs due to ionization. Under normal atmospheric conditions, an electric field of about 30,000 V/cm, or 3000 kV/m, is required to ionize air. It would seem that to find the voltage, it is enough to multiply this figure by the average length of the lightning channel between the cloud and the ground - 3000 m in our temperate latitudes. We get something disproportionate - 9,000,000 kV or, what is the same - 9 billion volts.
In reality, about 100 times less lightning is needed. The reason is that its channel is not created simultaneously along the entire length from the cloud to the ground, but sequentially. The strong field region exists only at the channel head, and in the already created plasma behind the head it is incomparably weaker. As the channel lengthens, the region of strong field moves from the cloud to the ground. A good analogy would be an excavator digging a drainage ditch. Earth layer is violated only at the location of the bucket. However, a ready-made channel remains along the entire route of the vehicle. It can stretch for at least tens of kilometers, if, of course, the soil is fixed and does not crumble.
The picture is similar with the lightning ionization zone. It moves from the cloud to the surface of the earth very quickly, at a speed of (2 - 3)´105 m/s, spending 10 - 15 ms along the entire path. But on the scale of ionization processes, a millisecond is not a short time. The plasma channel behind the head must necessarily maintain its initially high conductivity throughout the entire development period. To do this, the air in the channel must be heated to at least 5000 - 60000. Therefore, cold lightning does not happen.
100 million volts is the typical voltage that a lightning channel delivers to ground.

2. Charge of thundercloud and lightning
Answer to the question about charge Q gives knowledge of electric potential U. They are connected to each other through electrical capacitance C, Q =C.U.. In our case, we should talk about the capacity of the thundercloud and the lightning channel. Research has shown that the cloud is not uniformly charged. In its volume, individual areas with a large electrical charge clearly stand out. They are called thunderstorm cells. The characteristic radius of a thunderstorm cell is 1 km. With a known radius r the electrical capacitance of the cell is approximately equal to WITH» 4pe0 r. Here e0 = (36p´109)-1 F/m is the dielectric constant of vacuum. An approximate estimate can be made easier by remembering that the capacitance of a body in picofarads is close to its radius in centimeters. This means that the capacitance of a thunderstorm cell with a radius of 1 km (105 cm) is estimated as 105 pF or 0.1 μF. Multiplying by 100 MV we get 10 C - a completely reliable estimate for the minimum charge of a thundercloud cell.
Cells can be of different radii (up to tens of kilometers) and carry a potential significantly exceeding 100 MV. Therefore, a charge of 100 C is also quite realistic.
The lightning channel itself, like any small-radius conductor, has a capacity of about 10 picofarads per meter of length. With a length of 3000 m this gives approximately 0.03 µF for the lightning as a whole. Lightning charged to a potential of 100 MV lowers the charge to the ground Q =CU= 0.03·10-6´108 = 3 Cl. And again, the resulting figure corresponds well to reality.

This section will not please fans of non-science fiction who like the idea of ​​using lightning as a means of free electricity. There is very little energy. Its value is given by the product of the potential and the lightning charge, W=UQ» 108´3 = 3·108 J = 3·105 kJ. For a modern apartment with a load of 2 kWh, this will last about 40 hours.
It remains to remember that all this energy is not delivered by lightning to the ground, but is more or less evenly distributed along a channel several kilometers long.
Lightning is useless as a source of energy.
“Just don’t break it, lightning has enough energy for major troubles.”

When a lightning channel touches the ground or a ground structure, it acquires their zero potential. To do this, the charge of the channel must flow into the ground. The rapid process of charge neutralization is called the main stage of lightning.
Even with ideal conductivity, the channel cannot lose its charge instantly. A wave process propagates through the channel, which is characterized by wave resistance Z. Any long conductor, for example, a television cable, has a parameter of this kind. There the wave impedance is 75 Ohms. The lightning channel has a value Z about 7–10 times more, about 500 Ohms. Ohm's law gives a rough estimate of the lightning current I M = U/Z"108/500 = 200,000 A.
For extremely strong lightning, this is exactly the current. For many others, it is noticeably weaker due to the limited conductivity of the plasma channel and the partial loss of voltage by the channel when moving from the cloud to the ground. Direct measurements show that with a probability of 50% the lightning current is not less than 30 kA, in 5% of lightnings (strong lightning) it exceeds 80 kA and in the same 5% (weak lightning) it is less than 15 kA. Lightning with a current of 100 kA is recorded in less than 2%, and lightning with a current of 200 kA is so rare that their probability can only be estimated very roughly. Most likely, it is at the level of 0.1%.

It is determined by the charge that lightning delivers to the ground. For temperate latitudes, incl. and for almost the entire territory of Russia, approximately 90% of lightning is negative. The numbers presented in the previous section characterize their currents. The remaining 10% of lightning middle zone positive. Today it is not entirely clear why they are more powerful. With a probability of at least 5% their current exceeds 250 kA. The average current of positive lightning does not differ so much. A 50% probability here corresponds to a current of 35 kA, while for negative lightning this value is 30 kA.

The lightning channel often appears to flicker. This is not a visual defect, but a completely objective effect. Often several discharges follow the same trace at intervals of up to 0.1 s. Such long pauses are already visible to the eye. Lightning with several consecutive discharges is called multicomponent. Negative lightning has on average 3–4 components. Positive lightning has no subsequent components.
Subsequent components are observed in approximately 65% ​​of lightning strikes. The current of subsequent components is on average approximately 2 times less than that of the first, the parameters of which are given in Section 4.

The growth rate of the lightning current pulse is a very important parameter. It determines the EMF of magnetic induction in the electrical circuits of a structure struck by lightning. The duration of the lightning current pulse is no less important. It is associated with thermal and electromechanical effects. The average duration of the front of the first component of negative lightning is close to 5 μs, and the average pulse duration (at the 0.5 level) is about 75 μs. In subsequent components, the current pulse is approximately half as long, but it can increase very quickly, on average in less than 1 μs, and sometimes an order of magnitude faster.
Positive lightning has the longest current, up to 1000 - 2000 μs. They are also distinguished by the most flat fronts - up to 100 μs.

This parameter is most significant for practical lightning protection. The regulatory documents of all countries include maps of the intensity of thunderstorm activity. Using them, you can determine the annual average number of lightning strikes per unit of land surface for a given region. The only pity is that it is difficult to discern details on such maps. At best, one can estimate an area of ​​the country on average. In the polar regions of Russia, thunderstorm activity is not taken into account. In the main part of the territory there are 2 - 4 lightning strikes per year per 1 km2 of the earth's surface. In the most thunderstorm-prone areas of the Caucasus, the specific number of strikes approaches 10.
Many the developed countries covered by a system of remote direction finding of lightning discharges, which operates in on-line mode. Such a system provides commercial services; in particular, you can order samples based on the frequency of damage to a specific area of ​​the earth’s surface for the required observation period. The error in pinpointing lightning strike locations does not exceed 200–500 m. The territory of Russia is not entirely within the scope of observation of such systems.

According to operating experience, the higher the structure, the more lightning it collects. The last word It was not placed by chance. Elevated objects actually attract lightning. It goes like this. The electric charge of lightning approaching the ground increases the electric field at the surface of the earth and at the top of the ground structure. If the lightning is not too far away in the radial direction, the enhanced field is sufficient not only to ionize the air at the top of the structure, but also to develop a plasma channel from it. This is the so-called counter leader. It moves towards the lightning channel. The meeting of the channels completes the process.
The higher the object, the stronger the electric field at its top, the earlier the oncoming leader starts and the more efficiently it moves towards the lightning. This means that the meeting of channels can occur at a greater distance from the object. This is why the height of an object directly determines the radius of lightning contraction. For evaluation calculations from operating experience it is assumed that the contraction radius R supposedly approximately equal tripled height of the object.

Using the contraction radius, it is easy to estimate the expected number of lightning strikes into an object of height h. In the plan, outline the outer perimeter of the object with a line spaced from it by R say = 3 h. The line will limit the area of ​​lightning contraction. Calculate it (very approximately) in any available way and, respecting the dimension, multiply it by the specific number of lightning strikes for a given region. Obtain the average expected number of direct lightning strikes per year of operation. Let, for example, we are talking about a tower high h = 100 m. Then the contraction area is limited by a circle with radius R say = 3 h= 300 m and occupies an area S they say = p R mol2 = 282600 m2 » 0.282 km2. For an area where the density of lightning strikes is n supposedly = 2 impacts per km2 per year, to be expected N= n they say S they say » 0.56 lightning strikes per year, i.e. slightly more often than 1 blow for every 2 years of operation.
Another example. Individual residential building 6 x 10 m2 and height h = 6 m. If you do not pay attention to the roundings in the corners, the contraction area, with some overestimation, can be estimated at 42x46 = 1932 m2 » 0.02 km2. At the same density of lightning strikes n mol = 2 strikes per km2 per year, this gives 0.04 lightning strikes per year or 1 strike for 25 years of operation of the building.
Calculation by contraction area gives good results for open, flat areas. In an area of ​​continuous construction, for example in a city, the actual number of impacts may be noticeably less than the estimated number, since closely located buildings mutually shield each other (their contraction areas overlap). In contrast, in hilly or mountainous areas, when the height of the ground is added to the true height of the building, the actual number of impacts may exceed the calculated number. In such conditions, you need to contact specialists and use calculation programs.

There is a serious mistake hidden in the title. Structures over 200 m high in flat areas do not so much absorb lightning strikes as send them into a thundercloud. These are the so-called ascending lightning. Unlike ordinary downward ones, they start from the top of a high-altitude object and move in the direction of the thundercloud. Driving force again is the electric field of the atmosphere. In thunderstorm conditions, its intensity at the surface of the earth lies within 20 kV/m. Let's say, along the Ostankino TV tower over a length of 500 m, 20x500 = 10,000 kV = 10 MV is collected. This field is forced out of the metal of the tower to its top, where rising lightning is excited. Research has shown that not very distant ordinary downward lightning acts as a fuse here. By themselves, they do not fall into a high-rise structure, but contribute to the start of an ascending discharge. Therefore, the method for counting the number of lightning strikes can not be changed and again use the concept contraction areas . In the end, it makes no difference whether the object is struck by the downward lightning itself or whether it is struck by the upward lightning provoked by it. The calculation result is quite reliable. For example, the Ostankino TV tower is h = 540 m has a contraction radius R say = 3 h = 1.62 km, which limits the contraction area S they say = p R mol2 = 8.2 km2. With the specific density of lightning discharges in Moscow n mol = 3 this gives about 25 lightning strikes per year, which is very close to the results of long-term observations (in total 27 - 28 lightning strikes per year, of which only about 10% are “real” downward).

11. Thermal effects of lightning
The temperature in the lightning channel can rise to 30,000 K. Hence its ability to set fire and burn.
Lightning is a rather specific igniter, because the combustion products are carried away by a strong shock wave. However, fire caused by lightning is possible. In multicomponent lightning, between the components and after the last of them, a current of 100 - 200 A passes through the channel within tenths of a second. Such a weak current does not create a shock wave, but it keeps the temperature in the channel within 6000 - 7000 K. In terms of ignition ability, this comparable to the arc of a welding machine.
The gigantic scale of lightning makes it possible to see some absolutely cyclopean damage due to penetrations and burns of metal surfaces. In fact, they are more than modest. When the metal tip of a flagpole that had stood there for several years was removed from the top of a television tower in Moscow, traces of molten metal were seen on it, each no more than a centimeter in diameter.

The energy released from the entire lightning channel heats the air aimlessly, and the metal is heated only by what is emitted at the point of contact of the plasma with the metal surface. As a rule, no more than 2000 J are consumed “usefully”. Tests have shown that a metal wall with a thickness of 4 mm or more cannot under any circumstances be burned through by lightning. Therefore, the rules for lightning protection in all countries do not allow the installation of lightning rods near objects with a metal shell of such thickness.
Lightning can burn through roofing iron or metal roofing. About 2 g of metal goes into the melt, and the characteristic radius of the hole in most cases does not exceed 1 cm. The lightning channel does not penetrate inside the resulting hole.
A big nuisance is the transition contacts at the junctions of current conductors through which lightning current passes. Lightning current value I M at average pulse duration D t allocates in contact resistance R con energy
W con = R con I M2D t. For powerful lightning with a current of 100 kA at D t= 100 µs in contact with R con = 0.01 Ohm (very high quality connection) 10 kJ is released. This is enough to heat a conductor weighing 0.1 kg by 2100. It remains to be noted that due to the short duration of the lightning current, practically no heat is removed from the contact.
If necessary, contacts are still used, but they must be done with the utmost care. The contact area must be large and the pressing force extremely strong. Then the contact resistance will be low, and the released heat will be distributed over a large mass of metal and will not raise the temperature to a dangerous level.

12. Electrohydraulic effect
On forest edges or clearings you can find strangely damaged trees. The impression is as if a giant beast with a wide clawed paw tore out a strip of bark several centimeters wide from the top of the head almost to the root. This is how lightning worked. Living wood is filled with moisture and is capable of conducting electricity. The largest part of the current flows along the outer part of the trunk adjacent to the bark. The energy released there rapidly evaporates moisture. Almost instantly, the generated steam sharply increases the pressure and tears the bark.
A similar phenomenon is characteristic of many gas-generating materials that are widely used in technology. For example, the destruction of underground cables is often associated with the evaporation of their plastic sheath or bitumen impregnation. The effect is no less from the evaporation of materials containing epoxy compound. Composite and cellular fiberglass materials also suffer from electrohydraulic effects. A shock wave also occurs in the air. It is generated by a very rapid expansion of a plasma channel with a strong current (hence the thunder). A sharp pressure drop occurs in any cavity, including in an aircraft engine. When lightning is very close, the shock wave can disrupt the flame and stop the jet engine. This phenomenon in aviation is known as engine surge. Fortunately, this is rare, and very rare in a multi-engine passenger airliner. In addition, a stopped engine can be started right in the air.

13. Mechanical effect of lightning current
The direct mechanical impact of lightning current rarely leads to serious damage. Flowing through a hollow tube, lightning current can compress it, change the angle of inclination of the conductors, deform the antenna, etc. Usually we are talking about some relatively weak technological elements on the external structures of the facility. Lightning cannot damage the structures responsible for the mechanical strength of the building. Measures of protection against mechanical influences are usually used only when the damaged part is a sensor of any measuring system and therefore maintaining its geometry is important to ensure the required hardware error.

14. Lightning strikes people and animals
A current of 0.1 A passing through the human body for 1 second is certainly fatal. The lightning current is 4–5 orders of magnitude greater. And although the time of its impact is measured in tens of microseconds, a person has little chance of surviving a direct lightning strike. Fortunately, a direct hit is a very rare event. A person 2 m tall in an open area pulls lightning onto himself from an area limited by a radius of only 6 m. The contraction area is close to 100 m2. With a specific lightning density of 3 strikes per year per square kilometer, you need to count on approximately 0.0003 lightning strikes per year, which is equivalent to one strike per 3300 years of life. If direct lightning strikes to a person do occur, it is due to the extremely large population of the Earth.
Indirect lightning exposure is much more likely. Whatever structure it hits, its current will eventually enter the ground and spread there. Then everything depends on the soil resistivity r. It varies within very wide limits. U fresh water r = 20 – 40 Ohm m, for chernozem r » 100 Ohm m, for wet sands and loams 200 – 400 Ohm m, for rocks 1000 – 10000 Ohm m (and sometimes much more). Resistance and current determine the electric field in the soil. Its tension is E= r J, and the current density J can be estimated from the assumption that the lightning current I the pier spreads symmetrically from the point of impact in a hemispherical volume. On distance r the current density will be equal
,
and the tension accordingly

At stride length D d the field creates a step voltage
,
which affects a person. If, for example, I mol = 100 kA, then in soil of moderate conductivity (r = 200 Ohm m) at a distance of 20 m from the point of impact at a step length of 0.7 m, approximately 5500 V is collected, which cannot in any way be considered safe.
This is why it is not recommended to be near a thunderstorm. tall trees, especially isolated ones or at the edge of the forest. The height of a tree is 10 times greater than that of a person, and therefore lightning strikes it 100 times more often. The spread of current through the root system and further along the ground causes dangerous step voltages.
Since the effective stress is proportional to the length of the step, or rather, the distance between the points of contact of the body with the ground, it is more dangerous to sit or lie down in a thunderstorm than to stand with your legs clenched (at attention). For the same reason, step stresses are more dangerous for large quadrupeds than for humans.
Lightning can also affect a person with its electromagnetic field. You can read about this in the corresponding section below.

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Many people are afraid terrible phenomenon nature - thunderstorms. This usually happens when the sun is covered by dark clouds, terrible thunder is booming and heavy rain is falling.

Of course, you should be afraid of lightning, because it can even kill or cause death. This has been known for a long time, which is why they came up with various means for protection from lightning and thunder (for example, metal poles).

What's going on up there and where does the thunder come from? And how does lightning occur?

Storm clouds

Usually huge. They reach several kilometers in height. It is not visually visible how everything is seething and boiling inside these thunderous clouds. These are turbulent currents of air, including droplets of water, with high speed move from bottom to top and vice versa.

The uppermost part of these clouds reaches -40 degrees in temperature, and drops of water falling into this part of the cloud freeze.

On the origin of thunderclouds

Before we learn where thunder comes from and how lightning occurs, let's briefly describe how thunderclouds form.

Most of these phenomena occur not over the water surface of the planet, but over the continents. In addition, thunderclouds intensively form over the continents of tropical latitudes, where the air near the earth's surface (as opposed to the air above the water surface) warms up strongly and rises quickly.

Usually, on the slopes of various elevations, a similar upward flow of heated air is formed, which draws in moist air from vast areas of the earth's surface and lifts it upward.

This is how the so-called cumulus clouds are formed, which turn into thunderclouds, described just above.

Now let’s clarify what lightning is, where does it come from?

Lightning and thunder

From those same frozen drops, pieces of ice are formed, which also move in the clouds at great speed, colliding, collapsing and charging with electricity. Those pieces of ice that are lighter and smaller remain at the top, and those that are larger melt, going down, again turning into droplets of water.

Thus, two electric charges arise in a thundercloud. At the top it is negative, at the bottom it is positive. When different charges meet, a powerful electrical discharge occurs and lightning occurs. It became clear where it comes from. What happens next? A flash of lightning instantly heats up and expands the air around it. The latter heats up so much that an explosion occurs. This is thunder, frightening all living things on earth.

It turns out that all these are manifestations. Then the next question arises about where the latter comes from, and in such large quantities. And where does it go?

Ionosphere

We found out what lightning is and where it comes from. Now a little about the processes that maintain the Earth's charge.

Scientists have found that the Earth's charge is generally small and amounts to only 500,000 coulombs (the same as 2 car batteries). Then where does that negative charge disappear, which is transferred by lightning closer to the surface of the Earth?

Usually, in clear weather, the Earth slowly discharges (a weak current constantly passes between the ionosphere and the Earth's surface through the entire atmosphere). Although air is considered an insulator, it contains a small proportion of ions, which allows current to exist throughout the entire atmosphere. Thanks to this, although slowly, the negative charge is transferred from the earth's surface to height. Therefore, the volume of the total charge of the Earth always remains unchanged.

Today, the most common opinion is that ball lightning is a special type of charge in the shape of a ball, which exists for quite a long time and moves along an unpredictable trajectory.

Today there is no single theory of the origin of this phenomenon. There are many hypotheses, but so far none has received recognition among scientists.

Usually, as eyewitnesses testify, it occurs during a thunderstorm or storm. But there are also cases of its occurrence in sunny weather. More often it is generated by ordinary lightning, sometimes it appears and descends from the clouds, and less often it appears unexpectedly in the air or can even come out of some object (pillar, tree).

Some interesting facts

We found out where thunder and lightning come from. Now a little about interesting facts regarding the above-described natural phenomena.

1. The Earth experiences approximately 25 million lightning flashes each year.

2. Lightning has an average length of approximately 2.5 km. There are also discharges that extend 20 km in the atmosphere.

3. There is a belief that lightning cannot strike twice in the same place. In reality this is not the case. Analysis results (by geographical map) locations of lightning strikes over the previous few years show that lightning can strike the same place several times.

So we found out what lightning is and where it comes from.

Thunderstorms are formed as a consequence of complex atmospheric phenomena on a planetary scale.

Every second, approximately 50 lightning flashes occur on planet Earth.

Doctor of Biological Sciences, Candidate of Physical and Mathematical Sciences K. BOGDANOV.

At any given time, more than 2,000 thunderstorms flash lightning in different parts of the Earth. Every second, about 50 lightning strikes the surface of the earth, and on average, every square kilometer of it is struck by lightning six times a year. B. Franklin also showed that lightning striking the ground from thunderclouds is electrical discharges that transfer to it a negative charge of several tens of coulombs, and the amplitude of the current during a lightning strike ranges from 20 to 100 kA. High-speed photography showed that the lightning discharge lasts several tenths of a second and consists of several even shorter discharges. Lightning has long been of interest to scientists, but even today we know only a little more about their nature than 250 years ago, although we were able to detect them even on other planets.

The ability to electrify by friction of various materials. The material from the rubbing pair, located higher in the table, is charged positively, and lower - negatively.

The negatively charged bottom of the cloud polarizes the surface of the Earth below it so that it becomes positively charged, and when conditions for electrical breakdown appear, a lightning discharge occurs.

Distribution of thunderstorm frequency over land and ocean surfaces. The darkest places on the map correspond to frequencies of no more than 0.1 thunderstorms per year per square kilometer, and the lightest - more than 50.

Umbrella with lightning rod. The model was sold in the 19th century and was in demand.

Shooting a liquid or laser at a thundercloud hanging over the stadium diverts the lightning bolt to the side.

Several lightning strikes caused by launching a rocket into a thundercloud. The left vertical line is the trail of the rocket.

A large “branched” fulgurite weighing 7.3 kg, found by the author on the outskirts of Moscow.

Hollow cylindrical fragments of fulgurite formed from melted sand.

White fulgurite from Texas.

Lightning is an eternal source of recharging the Earth's electric field. At the beginning of the 20th century, the Earth's electric field was measured using atmospheric probes. Its intensity at the surface turned out to be approximately 100 V/m, which corresponds to a total charge of the planet of about 400,000 C. The carrier of charges in the Earth's atmosphere are ions, the concentration of which increases with altitude and reaches a maximum at an altitude of 50 km, where under the influence of cosmic radiation an electrically conductive layer has formed - the ionosphere. Therefore, the Earth's electric field is the field of a spherical capacitor with an applied voltage of about 400 kV. Under the influence of this voltage from upper layers a current of 2-4 kA flows all the time into the lower ones, the density of which is 1-2. 10 -12 A/m 2, and energy is released up to 1.5 GW. And this electric field would disappear if there were no lightning! Therefore, in good weather The electrical capacitor - the Earth - is discharged and charged during a thunderstorm.

A person does not feel the Earth's electric field, since his body is a good conductor. Therefore, the Earth's charge is also on the surface of the human body, locally distorting the electric field. Under a thundercloud, the density of positive charges induced on the ground can increase significantly, and the electric field strength can exceed 100 kV/m, 1000 times its value in good weather. As a result, the positive charge of each hair on the head of a person standing under a thundercloud increases by the same amount, and they, pushing away from each other, stand on end.

Electrification - removal of “charged” dust. To understand how a cloud separates electrical charges, let’s remember what electrification is. The easiest way to charge a body is by rubbing it against another. Electrification by friction is the oldest method of producing electrical charges. The word “electron” itself, translated from Greek into Russian, means amber, since amber has always been negatively charged when rubbed against wool or silk. The magnitude of the charge and its sign depend on the materials of the rubbing bodies.

It is believed that a body, before it began to be rubbed against another, is electrically neutral. Indeed, if you leave a charged body in the air, then oppositely charged dust particles and ions will begin to stick to it. Thus, on the surface of any body there is a layer of “charged” dust that neutralizes the charge of the body. Therefore, electrification by friction is the process of partial removal of “charged” dust from both bodies. In this case, the result will depend on how much better or worse the “charged” dust is removed from rubbing bodies.

The cloud is a factory for the production of electrical charges. It's hard to imagine that a couple of the materials listed in the table are in the cloud. However, different “charged” dust can appear on bodies, even if they are made of the same material - it is enough for the surface microstructure to differ. For example, when a smooth body rubs against a rough one, both will become electrified.

A thundercloud is a huge amount of steam, some of which has condensed into tiny droplets or floes of ice. The top of a thundercloud can be at an altitude of 6-7 km, and the bottom can hang above the ground at an altitude 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 pieces of ice are in constant motion, caused by rising currents of warm air from the heated surface of the earth. Small pieces of ice are more easily carried away by rising air currents than large ones. Therefore, “nimble” small pieces of ice, moving to the top of the cloud, constantly collide with large ones. With each such collision, electrification occurs, in which large pieces of ice are charged negatively, and small ones - positively. Over time, positively charged small pieces of ice end up at the top of the cloud, and negatively charged large ones end up at the bottom. In other words, the top of a thunderstorm is positively charged and the bottom is negatively charged. Everything is ready for a lightning discharge, in which air breakdown occurs and the negative charge from the bottom of the thundercloud flows to the Earth.

Lightning is a greeting from space and a source of X-ray radiation. However, the cloud itself is not able to electrify itself enough to cause a discharge between its lower part and the ground. The electric field strength in a thundercloud never exceeds 400 kV/m, and electrical breakdown in the air occurs at a voltage greater than 2500 kV/m. Therefore, for lightning to occur, something other than an electric field is needed. In 1992, Russian scientist A. Gurevich from the Physical Institute named after. P. N. Lebedev RAS (FIAN) suggested that a kind of ignition for lightning could be cosmic rays- high-energy particles falling on the Earth from space at near-light speeds. 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 ground, the electrons are accelerated to near light speeds, ionizing their path and thus causing an avalanche of electrons moving with them towards the ground. The ionized channel created by this avalanche of electrons is used by lightning for discharge (see "Science and Life" No. 7, 1993).

Everyone who has seen lightning has noticed that it is not a brightly glowing straight line connecting the cloud and the ground, but a broken line. Therefore, the process of forming a conductive channel for a lightning discharge is called its “step leader”. Each of these “steps” is a place where electrons, accelerated to near-light speeds, stopped due to collisions with air molecules and changed the direction of movement. Evidence for this interpretation of the stepwise nature of lightning is flashes of X-ray radiation, coinciding with the moments when lightning, as if stumbling, changes its trajectory. Recent studies have shown that lightning is a fairly powerful source of X-ray radiation, the intensity of which can be up to 250,000 electron volts, which is about twice that used in chest X-rays.

How to trigger a lightning strike? It is very difficult to study what will happen in an unknown place and when. And this is exactly how scientists studying the nature of lightning have worked for many years. It is believed that the thunderstorm 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. To do this, B. Franklin flew a kite during a thunderstorm, ending with 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 the clouds to the ground. Franklin's experiments were extremely dangerous, and one of those who tried to repeat them, Russian academician G.V. Richman, died from a lightning strike in 1753.

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

Lightning: the giver of life and the engine of evolution. In 1953, biochemists S. Miller (Stanley Miller) and G. Urey (Harold Urey) showed that one of the "building blocks" of life - amino acids - can be obtained by passing an electric discharge through water in which the gases of the "primordial" atmosphere of the Earth are dissolved ( methane, ammonia and hydrogen). 50 years later, other researchers repeated these experiments and obtained the same results. Thus, the scientific theory of the origin of life on Earth assigns a fundamental role to lightning strikes.

When short current pulses are passed through bacteria, pores appear in their shell (membrane), through which DNA fragments of other bacteria can pass in, triggering one of the mechanisms of evolution.

Why are thunderstorms very rare in winter? F.I. Tyutchev, writing “I love thunderstorms in early May, when the first thunder of spring…”, knew that there are almost no thunderstorms in winter. For a thundercloud to form, rising currents of moist air are necessary. The concentration of saturated vapors increases with increasing temperature and is maximum in summer. The temperature difference on which the ascending air currents depend is greater, the higher its temperature at the surface of the earth, since at an altitude of several kilometers its temperature does not depend on the time of year. This means that the intensity of the ascending currents is also maximum in summer. That’s why we most often have thunderstorms in the summer, but in the north, where it’s cold even in the summer, thunderstorms are quite rare.

Why are thunderstorms more common over land than over sea? For a cloud to discharge, there must be a sufficient number of ions in the air below it. Air, consisting only of nitrogen and oxygen molecules, contains no ions and is very difficult to ionize even in an electric field. But if there are a lot of foreign particles in the air, for example dust, then there are also a lot of ions. Ions are formed by the movement of particles in the air in the same way as various materials are electrified by friction against each other. Obviously, there is much more dust in the air over land than over oceans. That's why thunderstorms thunder over land more often. It has also been noticed that, first of all, lightning strikes those places where the concentration of aerosols in the air is especially high - smoke and emissions from oil refining industry enterprises.

How Franklin deflected lightning. Fortunately, most lightning strikes occur between clouds and therefore pose no threat. However, it is believed that lightning kills more than a thousand people around the world every year. At least in the United States, where such statistics are kept, about 1,000 people suffer from lightning strikes every year and more than a hundred of them die. Scientists have long tried to protect people from this “punishment of God.” For example, the inventor of the first electric capacitor (Leyden jar), Pieter van Muschenbrouck (1692-1761), in an article on electricity written for the famous French Encyclopedia, defended traditional methods of preventing lightning - bell ringing and firing cannons, which he believed were quite effective.

Benjamin Franklin, trying to protect the Capitol of the capital of the state of Maryland, in 1775 attached a thick iron rod to the building, which rose several meters above the dome and was connected to the ground. The scientist refused to patent his invention, wanting it to begin serving people as soon as possible.

The news of Franklin's lightning rod quickly spread throughout Europe, and he was elected to all academies, including the Russian one. However, in some countries the devout population greeted this invention with indignation. The very idea that a person could so easily and simply tame the main weapon of “God’s wrath” seemed blasphemous. Therefore, in different places people, for pious reasons, broke lightning rods. A curious incident occurred in 1780 in the small town of Saint-Omer in northern France, where the townspeople demanded that the iron lightning rod mast be demolished, and the matter came to trial. The young lawyer, who defended the lightning rod from the attacks of obscurantists, based his defense on the fact that both the human mind and his ability to conquer the forces of nature are of divine origin. Everything that helps save a life is for the good, the young lawyer argued. He won the case and gained great fame. The lawyer's name was Maximilian Robespierre. Well, now the portrait of the inventor of the lightning rod is the most desirable reproduction in the world, because it adorns the well-known hundred dollar bill.

How to protect yourself from lightning using a water jet and a laser. Recently, a fundamentally new method of combating lightning was proposed. A lightning rod will be created from... a jet of liquid that will be shot from the ground directly into thunderclouds. Lightning liquid is a saline solution to which liquid polymers are added: the salt is intended to increase electrical conductivity, and the polymer prevents the jet from “breaking up” into individual droplets. The diameter of the jet will be about a centimeter, and the maximum height will be 300 meters. When the liquid lightning rod is finalized, it will be equipped with sports and children's playgrounds, where the fountain will turn on automatically when the electric field strength becomes high enough and the probability of a lightning strike is maximum. A charge will flow down a stream of liquid from a thundercloud, making lightning safe for others. Similar protection against lightning discharge can be done using a laser, the beam of which, ionizing the air, will create a channel for an electrical discharge away from crowds of people.

Can lightning lead us astray? Yes, if you use a compass. In the famous novel by G. Melville "Moby Dick" exactly such a case is described when a lightning discharge, which created a strong magnetic field, remagnetized the compass needle. However, the captain of the ship took a sewing needle, hit it to magnetize it, and replaced it with the damaged compass needle.

Can you be struck by lightning inside a house or airplane? Unfortunately yes! Lightning current can enter a house through a telephone wire from a nearby pole. Therefore, during a thunderstorm, try not to use a regular phone. It is believed that talking on a radiotelephone or mobile phone is safer. During a thunderstorm, you should not touch the central heating and water pipes that connect the house to the ground. For the same reasons, experts advise turning off all electrical appliances during a thunderstorm, including computers and televisions.

As for airplanes, generally speaking, they try to fly around areas with thunderstorm activity. And yet, on average, one of the planes is struck by lightning once a year. Its current cannot affect passengers; it flows down the outer surface of the aircraft, but it can damage radio communications, navigation equipment and electronics.

Fulgurite is fossilized lightning. During a lightning discharge, 10 9 -10 10 joules of energy are released. Most of it is spent creating a shock wave (thunder), heating the air, flashing light and other electromagnetic waves, and only a small part is released at the place where the lightning enters the ground. However, even this “small” part is enough to cause a fire, kill a person and destroy a building. Lightning can heat up the channel through which it moves up to 30,000 ° C, five times higher than the temperature on the surface of the Sun. The temperature inside the lightning is much higher than the melting point of sand (1600-2000°C), but whether the sand melts or not also depends on the duration of the lightning, which can range from tens of microseconds to tenths of a second. The amplitude of a lightning current pulse is usually equal to several tens of kiloamperes, but sometimes it can exceed 100 kA. The most powerful lightning strikes cause the birth of fulgurites - hollow cylinders of melted sand.

The word fulgurite comes from the Latin fulgur, meaning lightning. The longest excavated fulgurites went underground to a depth of more than five meters. Fulgurites are also called melts of solid rocks formed by a lightning strike; they are sometimes found in large numbers on rocky mountain tops. Fulgurites, consisting of melted silica, usually appear as cone-shaped tubes as thick as a pencil or a finger. Their inner surface is smooth and melted, and the outer surface is formed by grains of sand adhering to the melted mass. The color of fulgurites depends on the mineral impurities in the sandy soil. Most are tan, gray or black in color, but greenish, white or even translucent fulgurites are also found.

Apparently, the first description of fulgurites and their connection to lightning strikes was made in 1706 by Pastor David Hermann. Subsequently, many found fulgurites near people struck by lightning. Charles Darwin during trip around the world on the ship Beagle, discovered on the sandy shore near Maldonado (Uruguay) several glass tubes extending vertically down more than a meter into the sand. He described their sizes and associated their formation with lightning discharges. The famous American physicist Robert Wood received an “autograph” of the lightning that almost killed him:

"A severe thunderstorm had passed and the sky above us had already cleared. I walked across the field that separates our house from my sister-in-law's house. I walked about ten yards along the path when suddenly my daughter Margaret called me. I stopped for about ten seconds and barely moved further, when suddenly a bright blue line cut through the sky, with the roar of a twelve-inch cannon, striking the path twenty paces in front of me and raising a huge column of steam. I went further to see what trace the lightning had left. In the place where the lightning struck, there was a spot burnt clover about five inches in diameter, with a hole in the middle half an inch.... I returned to the laboratory, melted eight pounds of tin and poured it into the hole... What I dug out, when the tin hardened, looked like a huge, slightly curved dog-arp, heavy, as expected, in the handle and gradually converging towards the end. It was slightly longer than three feet" (quoted from V. Seabrook. Robert Wood. - M.: Nauka, 1985, p. 285).

The appearance of a glass tube in sand during a lightning discharge is due to the fact that there is always air and moisture between the grains of sand. The electric current of lightning in a fraction of a second heats the air and water vapor to enormous temperatures, causing an explosive increase in air pressure between grains of sand and its expansion, which Wood heard and saw, miraculously not becoming a victim of lightning. The expanding air forms a cylindrical cavity inside the molten sand. Subsequent rapid cooling fixes the fulgurite - a glass tube in the sand.

Often carefully dug out of sand, fulgurite is shaped like a tree root or branch with numerous shoots. Such branched fulgurites are formed when a lightning discharge strikes wet sand, which, as is known, has greater electrical conductivity than dry sand. In these cases, the lightning current, entering the soil, immediately begins to spread to the sides, forming a structure similar to the root of a tree , and the resulting fulgurite only repeats this shape. Fulgurite is very fragile, and attempts to remove adhered sand often lead to its destruction. This is especially true for branched fulgurites formed in wet sand.

Lightning is a giant electrical spark. When it hits buildings, it causes fires, splits large trees, and infects people. At any given time, more than 2,000 thunderstorms flash lightning in different parts of the Earth. Every second, about 50 lightning strikes the surface of the earth, and on average, every square kilometer of it is struck by lightning six times a year

Lightning is a giant electrical spark discharge in the atmosphere, usually occurring during a thunderstorm, resulting in a bright flash of light and accompanying thunder. Lightning has also been recorded on Venus, Jupiter, Saturn and Uranus. The current in a lightning discharge reaches 10-20 thousand amperes, so few people manage to survive after being struck by lightning.

The surface of the globe is more electrically conductive than air. However, the electrical conductivity of air increases with altitude. The air is usually positively charged, and the Earth is negatively charged. Water droplets in a thundercloud are charged due to the absorption of charged tiny particles (ions) in the air. A drop falling from a cloud has a negative charge at the top and a positive charge at the bottom. falling drops for the most part absorb negatively charged particles and acquire a negative charge. In the process of swirling in the cloud, water droplets are sprayed, with small drops flying with a negative charge, and large drops flying with a positive charge. The same thing happens with ice crystals at the top of the cloud. When they split, small ice particles acquire a positive charge and are carried by ascending currents to the upper part of the cloud, and large, negatively charged particles fall to the lower part of the cloud. As a result of the separation of charges, electric fields are created in the thundercloud and in the surrounding space. With the accumulation of large volumetric charges in a thundercloud, spark discharges (lightning) occur between individual parts of the cloud or between the cloud and the earth's surface. Lightning discharges vary in appearance. Linear branched lightning is most often observed, sometimes ball lightning and etc.

Lightning is of great interest not only as a peculiar natural phenomenon. It makes it possible to observe an electrical discharge in a gaseous medium at a voltage of several hundred million volts and a distance between electrodes of several kilometers.

In 1750, B. Franklin proposed to the Royal Society of London to conduct an experiment with an iron rod mounted on an insulating base and mounted on a high tower. He expected that when a thundercloud approached the tower, a charge of the opposite sign would be concentrated at the upper end of the initially neutral rod, and a charge of the same sign as at the base of the cloud would be concentrated at the lower end. If the electric field strength during a lightning discharge increases sufficiently, the charge from the upper end of the rod will partially flow into the air, and the rod will acquire a charge of the same sign as the base of the cloud.

The experiment proposed by Franklin was not carried out in England, but it was carried out in 1752 in Marly near Paris by the French physicist Jean d'Alembert. He used an iron rod 12 m long inserted into a glass bottle (which served as an insulator), but did not place it on the tower. May 10 his assistant reported that when a thundercloud was over the bar, sparks occurred when a grounded wire was brought near it.

Franklin himself, unaware of the successful experience realized in France, in June of the same year conducted his famous experiment with kite and observed electric sparks at the end of a wire tied to it. The following year, while studying the charges collected from the rod, Franklin determined that the bases of thunderclouds were usually negatively charged.

More detailed studies of lightning became possible at the end of the 19th century. thanks to the improvement of photographic methods, especially after the invention of an apparatus with rotating lenses, which made it possible to record rapidly developing processes. This type of camera was widely used in the study of spark discharges. It has been found that there are several types of lightning, with the most common being line, plane (in-cloud) and ball (air discharges).

Linear lightning has a length of 2-4 km and has a large current. It is formed when the electric field strength reaches a critical value and the ionization process occurs. The latter is initially created by free electrons, always present in the air. Under the influence of an electric field, electrons acquire high speeds and on their way to the Earth, colliding with air atoms, they split and ionize them. Ionization occurs in a narrow channel, which becomes conductive. The air is heating up. Through a channel of heated air, the charge from the cloud flows to the earth's surface at a speed of more than 150 km/h. This is the first stage of the process. When a charge reaches the Earth's surface between the cloud and the ground, a conductive channel is created through which charges move towards each other: positive charges from the Earth's surface and negative charges accumulated in the cloud. Linear lightning is accompanied by a strong rolling sound - thunder, reminiscent of an explosion. The sound appears as a result of the rapid heating and expansion of air in the channel, and then its equally rapid cooling and compression.

Flat lightning occurs within a thundercloud and appears as flashes of diffuse light.

Ball lightning consists of a luminous mass in the shape of a ball, slightly smaller soccer ball, moving at low speed in the direction of the wind. They burst with a big bang or disappear without a trace. Ball lightning appears after linear lightning. It often enters rooms through open doors and windows. The nature of ball lightning is not yet known. Air discharges of ball lightning, starting from a thundercloud, are often directed horizontally and do not reach the earth's surface.

To protect against lightning, lightning rods are created, with the help of which the lightning charge is carried into the ground along a specially prepared safe path.

A lightning discharge usually consists of three or more repeated strikes - 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). In general, the flash lasts about a second or less. A typical lightning development process can be described as follows. First, a weakly luminous leader discharge rushes from above to the earth's surface. When he reaches it, a brightly glowing return, or main, discharge passes from the ground up through the channel laid by the leader.

The leading discharge, as a rule, moves in a zigzag manner. The speed of its spread ranges from one hundred to several hundred kilometers per second. On its way, it ionizes air molecules, creating a channel with increased conductivity, through which the reverse discharge moves upward at a speed approximately one hundred times greater than that of the leading discharge. The size of the channel is difficult to determine, but the diameter of the leading discharge is estimated at 1–10 m, and the diameter of the return discharge is several centimeters.

Lightning discharges create radio interference by emitting radio waves in a wide range - from 30 kHz to ultra-low frequencies. The greatest emission of radio waves is probably in the range from 5 to 10 kHz. Such low-frequency radio interference is “concentrated” in the space between the lower boundary of the ionosphere and the earth’s surface and can spread to distances of thousands of kilometers from the source.

Lightning: the giver of life and the engine of evolution. In 1953, biochemists S. Miller (Stanley Miller) and G. Urey (Harold Urey) showed that one of the "building blocks" of life - amino acids - can be obtained by passing an electric discharge through water in which the gases of the "primordial" atmosphere of the Earth are dissolved ( methane, ammonia and hydrogen). 50 years later, other researchers repeated these experiments and obtained the same results. Thus, the scientific theory of the origin of life on Earth assigns a fundamental role to lightning strikes. When short current pulses are passed through bacteria, pores appear in their shell (membrane), through which DNA fragments of other bacteria can pass in, triggering one of the mechanisms of evolution.

How to protect yourself from lightning using a water jet and a laser. Recently, a fundamentally new method of combating lightning was proposed. A lightning rod will be created from... a jet of liquid that will be shot from the ground directly into thunderclouds. Lightning liquid is a saline solution to which liquid polymers are added: the salt is intended to increase electrical conductivity, and the polymer prevents the jet from “breaking up” into individual droplets. The diameter of the jet will be about a centimeter, and the maximum height will be 300 meters. When the liquid lightning rod is finalized, it will be equipped with sports and children's playgrounds, where the fountain will turn on automatically when the electric field strength becomes high enough and the probability of a lightning strike is maximum. A charge will flow down a stream of liquid from a thundercloud, making lightning safe for others. Similar protection against lightning discharge can be done using a laser, the beam of which, ionizing the air, will create a channel for an electrical discharge away from crowds of people.

Can lightning lead us astray? Yes, if you use a compass. In the famous novel by G. Melville "Moby Dick" exactly such a case is described when a lightning discharge, which created a strong magnetic field, remagnetized the compass needle. However, the captain of the ship took a sewing needle, hit it to magnetize it, and replaced it with the damaged compass needle.

Can you be struck by lightning inside a house or airplane? Unfortunately yes! Lightning current can enter a house through a telephone wire from a nearby pole. Therefore, during a thunderstorm, try not to use a regular phone. It is believed that talking on a radiotelephone or mobile phone is safer. During a thunderstorm, you should not touch the central heating and water pipes that connect the house to the ground. For the same reasons, experts advise turning off all electrical appliances during a thunderstorm, including computers and televisions.

As for airplanes, generally speaking, they try to fly around areas with thunderstorm activity. And yet, on average, one of the planes is struck by lightning once a year. Its current cannot affect passengers; it flows down the outer surface of the aircraft, but it can damage radio communications, navigation equipment and electronics.