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Report "hazardous factors of lightning discharges". Formation of lightning discharges Downdrafts and squall fronts

Report "hazardous factors of lightning discharges". Formation of lightning discharges Downdrafts and squall fronts

Branch of MBOU "Pervomaiskaya secondary general education

school" in the village of Novoarkhangelskoye

lightning bolts

Hazards

lightning discharges

Completed:

7th grade students

Pecheikin Maxim,

Bryksin Kirill

Few people do not experience a sense of anxiety, awe before a thunderstorm,

and especially during heavy thunderstorms.

Storm - a dangerous atmospheric phenomenon associated with the development of powerful cumulonimbus clouds, accompanied by multiple electrical discharges between clouds and the earth's surface, sound phenomena, heavy precipitation, often with hail.

The name "thunderstorm" is associated with the menacing nature of this natural phenomenon and great danger. In ancient times, people, not understanding the nature of a thunderstorm, but seeing the death of people and fires arising during a thunderstorm, associated this phenomenon with the wrath of the gods, God's punishment for sins.

A thunderstorm is an exceptionally beautiful natural phenomenon that causes a person to admire its power and beauty. 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 drops rapidly until the wind suddenly increases, and then begins to rise. As a rule, after a thunderstorm the weather improves, the air is transparent, fresh and clean, saturated with ions formed during lightning discharges. Many writers, poets, artists have expressed feelings of love and admiration for the thunderstorm in their works. Remember the wonderful Russian poet F.I. Tyutchev:

I love the storm in early May,

When spring, the first thunder,

As if frolicking and playing,

Rumbles in the blue sky.

Thunderstorms there are: local, frontal, night, in the mountains.

Most often, local (thermal) thunderstorms occur. These thunderstorms occur only in hot weather with high atmospheric humidity. As a rule, they are in the summer at noon or afternoon (12-16 hours). The mechanism of formation of electric charges in clouds is as follows. Water vapor in an ascending stream of warm air condenses at a height, and a lot of heat is released (it is known that if the evaporation process requires energy, then the condensation process is accompanied by the release of thermal energy; this is due to the difference in the internal energy of a substance in liquid and gaseous states) and ascending air streams are warmed up. The rising air is warmer than the surrounding air and expands until it becomes a thundercloud. In large thunderstorm clouds, ice crystals and water droplets are constantly hovering, which, under the influence of an upward flow, collide, crush or merge. As a result of their friction between themselves and against the air and crushing, positive and negative charges are formed. They separate and concentrate in different parts of the cloud. As a rule, positive charges accumulate in the upper part of the cloud, and negative charges accumulate in the lower part (closest to the ground). As a result, negative lightning discharges occur. Less often, the reverse picture of the formation of positive lightning can occur. Under the action of charges, a strong electrostatic field arises (the intensity of the electrostatic field can reach 100,000 V / m), and the potential difference between individual parts of the cloud, clouds or cloud and the earth reaches enormous values. The voltage between cloud and ground can reach 80×106 - 100×106V.

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 5--7 km. Warm layers of air invade 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 frontal thunderstorm occurs more often in summer, but unlike local thunderstorms that occur only on hot summer days, it can occur at other times of the year, even in winter.

A night thunderstorm is associated with the cooling of the earth at night and the formation of eddy currents of ascending air.

A thunderstorm in the mountains is explained by the difference in the amount of solar radiation that the southern and northern slopes of the mountains are exposed to. Night and mountain thunderstorms are short. There are 16 million thunderstorms on Earth every year.

Thunderstorm activity in different parts of our planet is different.World hotspots of thunderstorms :

Java Island - 220, Equatorial Africa - 150, Southern Mexico - 142, Panama - 132, Central Brazil - 106 thunderstorm days a year.

Thunderstorm activity in Russia:

Murmansk - 5, Arkhangelsk - 10 St. Petersburg - 15, Moscow - 20 thunderstorm days a year. As a rule, the further south (FOR the northern hemisphere of the Earth) and further north (FOR the southern hemisphere of the Earth), the higher the thunderstorm activity. Thunderstorms in the Arctic and Antarctic are very rare.

Types of lightning And their causes

Combination lightning and thunder called thunderstorm.

Every person should have knowledge about the nature of lightning, its danger and methods of protection.

Lightning- This spark discharge of static electricity accumulated in thunderclouds. Unlike the charges generated at work and at home, the electric charges accumulated in clouds are incommensurably greater. Therefore, the energy of a spark discharge (lightning) and the resulting currents are very high and pose a serious danger to humans, animals, buildings. Lightning is accompanied by a sound impulse - thunder.

For every square kilometer of the Earth's surface, there are 2-3 lightning strikes per year. The earth is most often struck by lightning from negatively charged clouds.

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

The widespread linear lightning, which any person encounters many times, looks like a winding branching line. Great-

The magnitude of the current in the channel of a linear lightning is on average 60-170x 103 amperes, lightning with a current of 290x 103 amperes has been registered. An average lightning carries an energy of 250 kW/h (900 MJ), and 2800 kW/h (10,000 MJ) is reported. Lightning energy is mainly realized in the form of light, heat and sound energies.

The 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 33 000 about s. As a result, the pressure rises sharply, the air expands, a shock wave occurs, accompanied by a sound impulse - thunder. Since the path of lightning is very tortuous, sound waves arise at different points and travel different distances, sounds of different strength and height appear - thunder peals. Sound waves undergo repeated reflections from the clouds, the earth, which causes a prolonged rumble. Thunder is not dangerous for a person and has only a psychological effect on him.

Before a thunderstorm and during it, occasionally in the dark, on the tops of tall, pointed objects (the tops of trees, the masts of ships, the tops of sharp rocks in the mountains, the crosses of churches, lightning rods, sometimes in the mountains on people and animals on a head, a raised hand) one can observe a glow, dubbed"Fire of Saint Elmo". This name is givenin ancient times by sailors who observed the glow on the tops of the masts of sailing ships. glow"Elmo's Lights" arises due to the fact that on tall pointed objects, the electric field strength created by the static electric charge of the cloud is especially high. As a result, air ionization begins, a glow discharge occurs and reddish glow tongues appear, sometimes shortening and lengthening again. No attempt should be made to extinguish these fires, as there is no combustion. At a high electric field strength, a beam of luminous filaments may appear. - corona discharge, which is sometimes accompanied by hissing."Elmo's Lights "may appear without the presence of thunderclouds - more often in the mountains with snow blizzards and dust storms. Climbers often meet"Fires of Elmo".

Linear lightning also occasionally occurs in the absence of thunderclouds. It is no coincidence that the saying arose -

"A bolt from the blue".

pearl lightning - a very rare and beautiful phenomenon. Appears immediately after the linear lightning and disappears gradually. Predominantly, the pearl lightning discharge follows a linear path. Lightning has the form of luminous balls located at a distance 7-12 m from each other, reminiscent of pearls strung on a string. Pearl Lightning can be accompanied by significant sound effects.

Ball lightning is also quite rare. For a thousand ordinary linear lightning, there are 2-3 ball. Ball lightning, as a rule, appears during a thunderstorm, more often towards its end, less often after a thunderstorm. It also occurs, but very rarely, in the complete absence of thunderstorms. It can be in the form of a ball, ellipsoid, pear, disk, and even a chain of connected balls. The color of lightning is red, yellow, orange-red, surrounded by a luminous veil. Sometimes lightning is dazzling white with very sharp outlines. Color is determined by the content of various substances in the air. The shape and color of the lightning may change during the discharge. The nature of ball lightning and the reasons for its occurrence are unclear. There are various hypotheses about the nature of ball lightning. For example, Academician Ya.I. Frenkel created a theory according to which ball lightning is an incandescent gaseous ball resulting from ordinary linear lightning and consisting of chemically active gases - mainly nitrogen oxide and monatomic nitrogen. Academician P.I. Kapitsa believes that ball lightning is a plasma clot in a relatively stable state. There are other hypotheses, but none of them can explain all the effects associated With ball lightning. It was not possible to measure the parameters of ball lightning and simulate it in laboratory conditions. Apparently, many observed unidentified flying objects (UFOs) are similar or close to ball lightning in nature.

August 7, 2014

Thunderstorm - what is it? Where do the lightnings that cut through the whole sky and the menacing peals of thunder come from? Thunderstorm is a natural phenomenon. Lightning, called electrical discharges, can form inside clouds (cumulonimbus), or between the earth's surface and clouds. They are usually accompanied by thunder. Lightning is associated with heavy rains, heavy winds, and often with hail.

Activity

Thunderstorm is one of the most dangerous natural phenomena. People struck by lightning survive only in isolated cases.

At the same time, approximately 1,500 thunderstorms operate on the planet. The intensity of the discharges is estimated at a hundred lightning per second.

The distribution of thunderstorms on Earth is uneven. For example, there are 10 times more of them over the continents than over the ocean. Most (78%) of lightning discharges are concentrated in the equatorial and tropical zones. Thunderstorms are especially frequent in Central Africa. But the polar regions (Antarctica, the Arctic) and lightning poles are practically invisible. The intensity of a thunderstorm, it turns out, is associated with a heavenly body. In middle latitudes, its peak occurs in the afternoon (daytime) hours, in the summer. But the minimum was registered before sunrise. Geographic features are also important. The most powerful thunderstorm centers are in the Cordillera and the Himalayas (mountainous regions). The annual number of "stormy days" is also different in Russia. In Murmansk, for example, there are only four, in Arkhangelsk - fifteen, Kaliningrad - eighteen, St. Petersburg - 16, in Moscow - 24, Bryansk - 28, Voronezh - 26, Rostov - 31, Sochi - 50, Samara - 25, Kazan and Yekaterinburg - 28, Ufa - 31, Novosibirsk - 20, Barnaul - 32, Chita - 27, Irkutsk and Yakutsk - 12, Blagoveshchensk - 28, Vladivostok - 13, Khabarovsk - 25, Yuzhno-Sakhalinsk - 7, Petropavlovsk-Kamchatsky - 1.

Thunderstorm development

How does it go? Thunderclouds only form under certain conditions. The presence of ascending moisture flows is obligatory, while there must be a structure where one fraction of the particles is in an icy state, the other in a liquid state. Convection, which will lead to the development of a thunderstorm, will occur in several cases.

Uneven heating of surface layers. For example, over water with a significant temperature difference. Over large cities, thunderstorm intensity will be somewhat stronger than in the surrounding area.

When cold air displaces warm air. The frontal convention often develops simultaneously with oblique and nimbostratus clouds (clouds).

When air rises in mountain ranges. Even small elevations can lead to increased cloud formations. This is forced convection.

Any thundercloud, regardless of its type, necessarily goes through three stages: cumulus, maturity, and decay.

Classification

Thunderstorms were classified for some time only at the place of observation. They were divided, for example, into spelling, local, frontal. Thunderstorms are now classified according to characteristics that depend on the meteorological environment in which they develop. Updrafts are formed due to the instability of the atmosphere. For the creation of thunderclouds, this is the main condition. The characteristics of such flows are very important. Depending on their power and size, various types of thunderclouds are formed, respectively. How are they divided?

1. Cumulonimbus single-cell, (local or intramass). Have hail or thunderstorm activity. Transverse dimensions from 5 to 20 km, vertical - from 8 to 12 km. Such a cloud "lives" up to an hour. After a thunderstorm, the weather practically does not change.

2. Multicell cluster. Here the scale is more impressive - up to 1000 km. A multi-cell cluster covers a group of thunderstorm cells that are at different stages of formation and development and at the same time form a single whole. How are they arranged? Mature thunderstorm cells are located in the center, decaying - on the leeward side. Their transverse dimensions can reach 40 km. Cluster multi-cell thunderstorms “give” gusts of wind (heavy, but not strong), downpour, hail. The existence of one mature cell is limited to half an hour, but the cluster itself can “live” for several hours.

3. Lines of squalls. These are also multicell thunderstorms. They are also called linear. They can be either solid or with gaps. Wind gusts are longer here (on the leading front). The multicell line appears as a dark wall of clouds when approached. The number of streams (both upstream and downstream) is quite large here. That is why such a complex of thunderstorms is classified as multi-cell, although the thunderstorm structure is different. The squall line is capable of producing intense downpour and large hail, but is more often “limited” by strong downdrafts. It often passes ahead of a cold front. In the pictures, such a system has the shape of a curved bow.

4. Supercell thunderstorms. Such thunderstorms are rare. They are especially dangerous for property and human life. The cloud of this system is similar to the single-cell cloud, since both differ in one upstream zone. But they have different sizes. Supercell cloud - huge - close to 50 km in radius, height - up to 15 km. Its boundaries may lie in the stratosphere. The shape resembles a single semicircular anvil. The speed of ascending streams is much higher (up to 60 m/s). A characteristic feature is the presence of rotation. It is this that creates dangerous, extreme phenomena (large hail (more than 5 cm), destructive tornadoes). The main factor for the formation of such a cloud is the environmental conditions. We are talking about a very strong convention with a temperature of +27 and a wind with a variable direction. Such conditions arise during wind shear in the troposphere. Formed in the updrafts, precipitation is transferred to the downdraft zone, which ensures a long life for the cloud. Precipitation is unevenly distributed. Showers are near the updraft, and hail is closer to the northeast. The rear of the thunderstorm may shift. Then the most dangerous zone will be near the main updraft.

There is also the concept of "dry thunderstorm". This phenomenon is quite rare, characteristic of the monsoons. With such a thunderstorm, there is no precipitation (they simply do not reach, evaporating as a result of exposure to high temperature).

Movement speed

In an isolated thunderstorm, it is about 20 km / h, sometimes faster. If cold fronts are active, the speed can be 80 km/h. In many thunderstorms, old thunderstorm cells are replaced by new ones. Each of them covers a relatively short distance (about two kilometers), but in the aggregate the distance increases.

electrification mechanism

Where do lightning come from? Electric charges around clouds and inside them are constantly moving. This process is rather complicated. It is easiest to imagine how electric charges work in mature clouds. The dipole positive structure dominates in them. How is it distributed? The positive charge is placed at the top, and the negative charge is placed below it, inside the cloud. According to the main hypothesis (this area of science can still be considered little explored), heavier and larger particles are negatively charged, while small and light ones have a positive charge. The former fall faster than the latter. This becomes the reason for the spatial separation of space charges. This mechanism is confirmed by laboratory experiments. Particles of ice pellets or hail can have a strong charge transfer. The magnitude and sign will depend on the water content of the cloud, the air (ambient) temperature, and the collision velocity (the main factors). The influence of other mechanisms cannot be excluded. Discharges occur between the earth and the cloud (or the neutral atmosphere or the ionosphere). It is at this moment that we observe flashes dissecting the sky. Or lightning. This process is accompanied by loud peals (thunder).

Thunderstorm is a complex process. It can take many decades, and perhaps even centuries, to study it.

Storm - an atmospheric phenomenon in which electrical discharges occur inside the clouds or between the cloud and the earth's surface - lightning, accompanied by thunder. As a rule, a thunderstorm is formed in powerful cumulonimbus clouds and is associated with heavy rain, hail and squalls.

Thunderstorm is one of the most dangerous natural phenomena for humans: in terms of the number of recorded deaths, only floods lead to greater human losses.

Storm

Distribution of lightning discharges over the Earth's surface

There are approximately ten times less thunderstorms over the ocean than over the continents. About 78% of all lightning discharges are concentrated in the tropical and equatorial zone (from 30° north latitude to 30° south latitude). The maximum thunderstorm activity occurs in Central Africa. There are practically no thunderstorms in the polar regions of the Arctic and Antarctic and over the poles. The intensity of thunderstorms follows the sun: the maximum thunderstorms occur in the summer (in the middle latitudes) and in the daytime afternoon hours. The minimum recorded thunderstorms occur before sunrise. Thunderstorms are also affected by geographical features of the area: strong thunderstorm centers are located in the mountainous regions of the Himalayas and the Cordillera.

Development stages of a thundercloud

The necessary conditions for the formation of a thundercloud are the presence of conditions for the development of convection or another mechanism that creates ascending flows of moisture sufficient for the formation of precipitation, and the presence of a structure in which some of the cloud particles are in a liquid state, and some are in an icy state. Convection leading to the development of thunderstorms occurs in the following cases:

With uneven heating of the surface layer of air over a different underlying surface. For example, over the water surface and land due to differences in water and soil temperatures. Over large cities, the intensity of convection is much higher than in the vicinity of the city.

When warm air rises or is displaced by cold air at atmospheric fronts. Atmospheric convection at atmospheric fronts is much more intense and more frequent than during intramass convection. Often, frontal convection develops simultaneously with nimbostratus clouds and extensive precipitation, which masks the resulting cumulonimbus clouds.

When air rises in areas of mountain ranges. Even small elevations in the terrain lead to increased cloud formation (due to forced convection). High mountains create especially difficult conditions for the development of convection and almost always increase its frequency and intensity.

All thunderclouds, regardless of their type, successively go through the stages of a cumulus cloud, the stage of a mature thundercloud and the stage of decay.

Thundercloud classification

At one time, thunderstorms were classified according to where they were observed, such as localized, frontal, or orographic. It is now more common to classify thunderstorms according to the characteristics of the thunderstorms themselves, and these characteristics are mainly dependent on the meteorological environment in which the thunderstorm develops.

The main necessary condition for the formation of thunderclouds is the state of instability of the atmosphere, which forms updrafts. Depending on the magnitude and power of such flows, thunderclouds of various types are formed.

single cell cloud

Single-cell cumulonimbus clouds develop on days with weak winds in a low-gradient baric field. They are also called intramass or local thunderstorms. They consist of a convective cell with an upward flow in its central part. They can reach lightning and hail intensity and quickly collapse with precipitation. The dimensions of such a cloud are: transverse - 5-20 km, vertical - 8-12 km, life expectancy - about 30 minutes, sometimes - up to 1 hour. Serious weather changes after a thunderstorm do not occur.

The life cycle of a single cell cloud

A thunderstorm begins with a fine weather cumulus cloud (Cumulus humilis). Under favorable conditions, the resulting cumulus clouds grow rapidly both in the vertical and horizontal directions, while the updrafts are located almost throughout the volume of the cloud and increase from 5 m/s to 15-20 m/s. Downstreams are very weak. Ambient air actively penetrates into the cloud due to mixing at the boundary and top of the cloud. The cloud passes into the Cumulus mediocris stage. The smallest water drops formed as a result of condensation in such a cloud merge into larger ones, which are carried away by powerful upward flows. The cloud is still homogeneous, consists of water droplets held by an ascending flow - precipitation does not fall. In the upper part of the cloud, when water particles enter the zone of negative temperatures, the drops gradually begin to turn into ice crystals. The cloud becomes a powerful cumulus cloud (Cumulus congestus). The mixed composition of the cloud leads to the enlargement of cloud elements and the creation of conditions for precipitation. Such a cloud is called a cumulonimbus cloud (Cumulonimbus) or a bald cumulonimbus cloud (Cumulonimbus calvus). Vertical flows in it reach 25 m/s, and the level of the summit reaches a height of 7–8 km.

Evaporating precipitation particles cool the surrounding air, which leads to a further increase in downdrafts. At the stage of maturity, both ascending and descending air currents are present in the cloud at the same time.

At the decay stage, the cloud is dominated by downdrafts, which gradually cover the entire cloud.

Multicell cluster thunderstorms

Scheme of a multi-cell thunderstorm structure

This is the most common type of thunderstorm associated with mesoscale (having a scale of 10 to 1000 km) disturbances. A multi-cell cluster consists of a group of thunderstorm cells moving as a unit, although each cell in the cluster is at a different stage in the development of a thundercloud. Mature thunderstorm cells are usually located in the central part of the cluster, while decaying cells are located on the leeward side of the cluster. They have transverse dimensions of 20-40 km, their tops often rise to the tropopause and penetrate into the stratosphere. Multi-celled cluster thunderstorms can produce hail, showers, and relatively weak squalls. Each individual cell in a multi-cell cluster is in a mature state for about 20 minutes; the multi-cell cluster itself can exist for several hours. This type of thunderstorm is usually more intense than a single cell thunderstorm, but much weaker than a supercell thunderstorm.

Multicell line thunderstorms (squall lines)

Multicell line thunderstorms are a line of thunderstorms with a long, well-developed gust front on the front front line. The squall line may be continuous or contain gaps. The approaching multicell line looks like a dark wall of clouds, usually covering the horizon from the western side (in the northern hemisphere). A large number of closely spaced ascending/descending air currents allows us to qualify this complex of thunderstorms as a multi-cell thunderstorm, although its thunderstorm structure differs sharply from a multi-cell cluster thunderstorm. Squall lines can produce large hail and intense downpours, but they are more commonly known as systems that create strong downdrafts. The squall line is similar in properties to a cold front, but is a local result of thunderstorm activity. Often a squall line occurs ahead of a cold front. On radar images, this system resembles a curved bow (bow echo). This phenomenon is typical for North America, in Europe and the European territory of Russia it is observed less frequently.

Supercell thunderstorms

Vertical and horizontal structure of a supercell cloud

A supercell is the most highly organized thundercloud. Supercell clouds are relatively rare, but pose the greatest threat to human health and life and property. A supercell cloud is similar to a single cell cloud in that both have the same updraft zone. The difference is that the size of the cell is huge: a diameter of about 50 km, a height of 10-15 km (often the upper boundary penetrates into the stratosphere) with a single semicircular anvil. The speed of the ascending flow in a supercell cloud is much higher than in other types of thunderclouds: up to 40–60 m/s. The main feature that distinguishes a supercell cloud from other types of clouds is the presence of rotation. A rotating updraft in a supercell cloud (called in radar terminology) mesocyclone), creates extreme weather events, such as a giant hail(more than 5 cm in diameter), heavy winds up to 40 m/s and strong destructive tornadoes. Environmental conditions are a major factor in the formation of a supercell cloud. A very strong convective instability of the air is needed. The air temperature near the ground (before a thunderstorm) should be +27 ... +30 and higher, but the main necessary condition is the wind of a variable direction, which causes rotation. Such conditions are achieved with wind shear in the middle troposphere. Precipitation formed in the updraft is carried along the upper level of the cloud by a strong flow into the downdraft zone. Thus, the zones of the ascending and descending flows are separated in space, which ensures the life of the cloud for a long period of time. There is usually light rain at the leading edge of a supercell cloud. Heavy rainfall occurs near the updraft zone, while the heaviest precipitation and large hail fall to the northeast of the main updraft zone. The most dangerous conditions occur close to the main updraft area (usually displaced to the rear of the thunderstorm).

Supercell (English) super And cell- cell) - a type of thunderstorm, characterized by the presence of a mesocyclone - a deep, strongly rotating updraft. For this reason, such storms are sometimes called rotating thunderstorms. Of the four types of thunderstorms according to Western classifications (supercell, squalline, multicell and singlecell), supercells are the least common and may pose the greatest danger. Supercells are often isolated from other thunderstorms and can have a front span of up to 32 kilometers.

Supercell at sunset

Supersells are often divided into three types: classic; low precipitation (LP); and high precipitation (HP). LP-type supercells tend to form in drier climates such as the highland valleys of the United States, while HP-type supercells are more common in wetter climates. Supercells can occur anywhere in the world if the weather conditions are right for them to form, but they are most common in the US Great Plains, an area known as the Tornado Valley. They can also be observed in the plains in Argentina, Uruguay and southern Brazil.

Physical characteristics of thunderclouds

Airborne and radar studies show that a single thunderstorm cell usually reaches a height of about 8-10 km and lives for about 30 minutes. An isolated thunderstorm usually consists of several cells in various stages of development and lasts on the order of an hour. Large thunderstorms can reach tens of kilometers in diameter, their peak can reach heights of over 18 km, and they can last for many hours.

Upstream and downstream

Updrafts and downdrafts in isolated thunderstorms typically have a diameter of 0.5 to 2.5 km and a height of 3 to 8 km. Sometimes the diameter of the updraft can reach 4 km. Near the surface of the earth, the streams usually increase in diameter, and the speed in them decreases compared to the streams located above. The characteristic speed of the updraft lies in the range from 5 to 10 m/s and reaches 20 m/s in the upper part of large thunderstorms. Research planes flying through a thundercloud at an altitude of 10,000 m record updraft speeds in excess of 30 m/s. The strongest updrafts are observed in organized thunderstorms.

Flurries

Before the August 2010 squall in Gatchina

In some thunderstorms, intense downdrafts develop, creating destructive winds on the surface of the earth. Depending on the size, such downstreams are called flurries or microstorms. A squall with a diameter of more than 4 km can create winds up to 60 m/s. Microsqualls are smaller, but create wind speeds up to 75 m/s. If the thunderstorm that generates the squall is formed from sufficiently warm and moist air, then the microsquall will be accompanied by intense rain showers. However, if the thunderstorm is formed from dry air, the precipitation may evaporate during the fall (airborne precipitation bands or virga) and the microsquall will be dry. Downdrafts are a serious hazard to aircraft, especially during takeoff or landing, as they create wind near the ground with sudden changes in speed and direction.

Vertical development

In general, an active convective cloud will rise until it loses its buoyancy. The loss of buoyancy is due to the load created by precipitation formed in the cloudy environment, or mixing with the surrounding dry cold air, or a combination of these two processes. Cloud growth can also be stopped by a blocking inversion layer, i.e. a layer where air temperature rises with height. Thunderclouds usually reach a height of about 10 km, but sometimes reach heights of more than 20 km. When the moisture content and instability of the atmosphere are high, then with favorable winds, the cloud can grow to the tropopause, the layer that separates the troposphere from the stratosphere. The tropopause is characterized by a temperature that remains approximately constant with increasing altitude and is known as a region of high stability. As soon as the updraft begins to approach the stratosphere, pretty soon the air at the top of the cloud becomes colder and heavier than the surrounding air, and the growth of the top stops. The height of the tropopause depends on the latitude of the area and on the season of the year. It varies from 8 km in the polar regions to 18 km and higher near the equator.

When a cumulus cloud reaches the blocking layer of the tropopause inversion, it begins to spread outward and forms the “anvil” characteristic of thunderclouds. Wind blowing at the height of the anvil usually blows cloud material in the direction of the wind.

Turbulence

An aircraft flying through a thundercloud (it is forbidden to fly into cumulonimbus clouds) usually gets into a turbulence that throws the plane up, down and sideways under the influence of turbulent cloud flows. Atmospheric turbulence creates a feeling of discomfort for the aircraft crew and passengers and causes undesirable stresses on the aircraft. Turbulence is measured in different units, but more often it is defined in units of g - free fall acceleration (1g = 9.8 m / s 2). A flurry of one g creates turbulence that is dangerous for aircraft. In the upper part of intense thunderstorms, vertical accelerations up to three g were registered.

Thunderstorm movement

The speed and movement of a thundercloud depends on the direction of the earth, primarily by the interaction of the ascending and descending flows of the cloud with the carrier air flows in the middle layers of the atmosphere in which a thunderstorm develops. The speed of movement of an isolated thunderstorm is usually on the order of 20 km/h, but some thunderstorms move much faster. In extreme situations, a thundercloud can move at speeds of 65–80 km/h during the passage of active cold fronts. In most thunderstorms, as old thunderstorm cells dissipate, new thunderstorm cells emerge in succession. With a weak wind, an individual cell can travel a very short distance during its life, less than two kilometers; however, in larger thunderstorms, new cells are triggered by the downdraft flowing out of the mature cell, giving the impression of rapid movement that does not always match the direction of the wind. In large multicell thunderstorms, there is a pattern where a new cell forms to the right of the carrier airflow in the Northern Hemisphere and to the left of the carrier airflow in the Southern Hemisphere.

Energy

The energy that powers a thunderstorm is the latent heat released when water vapor condenses and forms cloud droplets. For every gram of water that condenses in the atmosphere, approximately 600 calories of heat are released. When the water droplets freeze at the top of the cloud, about 80 more calories per gram are released. The released latent thermal energy is partially converted into the kinetic energy of the upward flow. A rough estimate of the total energy of a thunderstorm can be made from the total amount of water that has precipitated from the cloud. Typical is an energy of the order of 100 million kilowatt-hours, which is roughly equivalent to a nuclear charge of 20 kilotons (although this energy is released in a much larger volume of space and over a much longer time). Large multi-celled thunderstorms can have 10 to 100 times more energy.

Downdrafts and squall fronts

Squall powerful thunderstorm front

Downdrafts in thunderstorms occur at altitudes where the air temperature is lower than the temperature in the surrounding space, and this stream becomes even colder when ice particles of precipitation begin to melt in it and cloud drops evaporate. The air in the downdraft is not only denser than the surrounding air, but it also carries a different horizontal angular momentum than the surrounding air. If a downdraft occurs, for example, at a height of 10 km, then it will reach the earth's surface with a horizontal speed that is noticeably greater than the wind speed near the earth. Near the ground, this air is carried forward before a thunderstorm at a speed greater than the speed of the entire cloud. That is why an observer on the ground will feel the approach of a thunderstorm along a stream of cold air even before the thundercloud is overhead. The downdraft propagating along the ground forms a zone with a depth of 500 meters to 2 km with a distinct difference between the cold air of the stream and the warm, moist air from which the thunderstorm is formed. The passage of such a squall front is easily determined by the increase in wind and a sudden drop in temperature. In five minutes, the air temperature can drop by 5°C or more. The squall forms a characteristic squall gate with a horizontal axis, a sharp drop in temperature, and a change in wind direction.

In extreme cases, the squall front created by the downdraft can reach speeds in excess of 50 m/s and cause damage to homes and crops. More often, severe squalls occur when an organized line of thunderstorms develops in high wind conditions at medium altitudes. At the same time, people may think that these destructions are caused by a tornado. If there are no witnesses who saw the characteristic funnel cloud of a tornado, then the cause of the destruction can be determined by the nature of the destruction caused by the wind. In tornadoes, destruction has a circular pattern, and a thunderstorm caused by a downdraft carries destruction mainly in one direction. The cold weather is usually followed by rain. In some cases, raindrops completely evaporate during the fall, resulting in a dry thunderstorm. In the opposite situation, typical for severe multi-cell and super-cell thunderstorms, there is heavy rain with hail, causing flash floods.

Tornadoes

A tornado is a strong small-scale eddy under thunderclouds with an approximately vertical but often curved axis. A pressure difference of 100–200 hPa is observed from the periphery to the center of the tornado. The wind speed in tornadoes can exceed 100 m/s, theoretically it can reach the speed of sound. In Russia, tornadoes occur relatively rarely, but they cause enormous damage. The highest frequency of tornadoes occurs in the south of the European part of Russia.

Livni

In small thunderstorms, the five-minute peak of intense precipitation can exceed 120 mm/hour, but the rest of the rain has an order of magnitude lower intensity. An average thunderstorm produces about 2,000 cubic meters of rain, but a large thunderstorm can produce ten times as much. Large organized thunderstorms associated with mesoscale convective systems can produce 10 to 1000 million cubic meters of precipitation.

Electrical structure of a thundercloud

Structure of charges in thunderclouds in different regions

The distribution and movement of electric charges in and around a thundercloud is a complex, continuously changing process. Nevertheless, it is possible to present a generalized picture of the distribution of electric charges at the cloud maturity stage. A positive dipole structure dominates, in which the positive charge is at the top of the cloud and the negative charge is below it inside the cloud. At the base of the cloud and below it, a lower positive charge is observed. Atmospheric ions, moving under the action of an electric field, form shielding layers at the cloud boundaries, masking the electrical structure of the cloud from an external observer. Measurements show that under various geographical conditions, the main negative charge of a thundercloud is located at altitudes with an ambient temperature of -5 to -17 °C. The greater the speed of the updraft in the cloud, the higher is the center of the negative charge. The space charge density is in the range of 1-10 C/km³. There is a significant proportion of thunderstorms with an inverse charge structure: - a negative charge in the upper part of the cloud and a positive charge in the inner part of the cloud, as well as with a complex structure with four or more zones of space charges of different polarity.

electrification mechanism

Many mechanisms have been proposed to explain the formation of the electrical structure of a thundercloud, and this area of science is still an area of active research. The main hypothesis is based on the fact that if larger and heavier cloud particles are predominantly negatively charged, and lighter small particles carry a positive charge, then the spatial separation of space charges occurs due to the fact that large particles fall at a higher speed than small cloud components. This mechanism is generally consistent with laboratory experiments that show strong charge transfer when particles of ice pellets (grains are porous particles of frozen water droplets) or hail particles interact with ice crystals in the presence of supercooled water droplets. The sign and magnitude of the charge transferred during the contacts depend on the temperature of the surrounding air and the water content of the cloud, but also on the size of the ice crystals, the velocity of the collision, and other factors. It is also possible the action of other mechanisms of electrification. When the magnitude of the volume electric charge accumulated in the cloud becomes large enough, a lightning discharge occurs between the areas charged with the opposite sign. A discharge can also occur between a cloud and the ground, a cloud and a neutral atmosphere, a cloud and the ionosphere. In a typical thunderstorm, two thirds to 100 percent of the discharges are intracloud discharges, intercloud discharges, or cloud-to-air discharges. The rest are cloud-to-ground discharges. In recent years, it has become clear that lightning can be artificially initiated in a cloud, which under normal conditions does not pass into the thunderstorm stage. In clouds that have zones of electrization and create electric fields, lightning can be initiated by mountains, high-rise buildings, aircraft or rockets that are in the zone of strong electric fields.

Zarnitsa - instantaneous flashes of light on the horizon during a distant thunderstorm.

During lightning, thunder peals are not heard due to the distance, but you can see flashes of lightning, the light of which is reflected from cumulonimbus clouds (mainly their tops). The phenomenon is observed in the dark, mainly after July 5, at the time of harvesting grain crops, so the lightning was timed by the people to the end of summer, the beginning of the harvest, and is sometimes called bakers.

snow storm

Scheme of the formation of a snow storm

A snow storm (also a snow storm) is a thunderstorm, a very rare meteorological phenomenon that occurs in the world 5-6 times a year. Instead of a heavy rainfall, heavy snow, freezing rain, or ice pellets fall. The term is used mainly in popular science and foreign literature (eng. thundersnow). In professional Russian meteorology, this term does not exist: in such cases, there is both a thunderstorm and heavy snow.

Cases of winter thunderstorms are noted in ancient Russian chronicles: thunderstorms in winter in 1383 (there was “a very terrible thunder and a whirlwind is strong”), in 1396 (in Moscow on December 25 “... there was thunder, and a cloud from the midday country”), in 1447 year (in Novgorod on November 13 "... at midnight a terrible thunder and lightning is great"), in 1491 (in Pskov on January 2 they heard thunder).

The process of occurrence of lightning discharges is well studied by modern science. It is believed that in most cases (90%) the discharge between the cloud and the ground has a negative charge. The remaining rarer types of lightning discharges can be divided into three types:

discharge from ground to cloud is negative;
positive lightning from cloud to ground;
a flash from the ground to a cloud with a positive charge.

Most of the discharges are fixed within the same cloud or between different thunderclouds.

Lightning formation: process theory

Formation of lightning discharges: 1 = approximately 6 thousand meters and -30°C, 2 = 15 thousand meters and -30°C.

Atmospheric electric discharges or lightning between the earth and the sky are formed with a combination and the presence of certain necessary conditions, an important of which is the appearance of convection. This is a natural phenomenon during which the air masses are warm enough and humid enough to be transferred by an ascending flow to the upper atmosphere. At the same time, the moisture present in them passes into a solid state of aggregation - ice floes. Thunderstorm fronts are formed when cumulonimbus clouds are located at an altitude of more than 15 thousand meters, and the streams ascending from the ground have a speed of up to 100 km / h. Convection leads to lightning discharges as the larger hailstones from the bottom of the cloud collide and rub against the surface of the lighter pieces of ice at the top.

Charges of a thundercloud and their distribution

Negative and positive charges: 1 = hailstone, 2 = ice crystals.

Numerous studies confirm that falling heavier hailstones formed at air temperatures warmer than -15°C are negatively charged, while light ice crystals formed at air temperatures colder than -15°C are usually positively charged. Air currents ascending from the ground raise positive light ice floes to higher layers, negative hailstones to the central part of the cloud and divide the cloud into three parts:

the topmost zone with a positive charge;
middle or central zone, partially negatively charged;
bottom with a partially positive charge.

Scientists explain the development of lightning in a cloud by the fact that the electrons are distributed in such a way that its upper part has a positive charge, and the middle and partially lower part has a negative charge. At times, this kind of capacitor is discharged. The lightning originating in the negative part of the cloud goes to the positive earth. In this case, the field strength required for a lightning discharge should be in the range of 0.5-10 kV/cm. This value depends on the insulating properties of the air.

Discharge distribution: 1 = approximately 6 thousand meters, 2 = electric field.

Cost calculation

Our facilities

JSC "Mosvodokanal", Sports and recreation complex of the rest house "Pyalovo"

Address of the object: Moscow region, Mytishchi district, village. Prussians, 25

Type of work: Design and installation of an external lightning protection system.

Composition of lightning protection: A lightning protection mesh is laid on the flat roof of the protected structure. The two chimneys are protected by installing lightning rods 2000 mm long and 16 mm in diameter. Hot-dip galvanized steel with a diameter of 8 mm (section 50 sq. mm in accordance with RD 34.21.122-87) was used as a lightning conductor. The down conductors are laid behind the downpipes on clamps with clamping terminals. For down conductors, a conductor made of hot-dip galvanized steel with a diameter of 8 mm was used.

GTPP Tereshkovo

Address of the object: Moscow city. Borovskoe sh., communal area "Tereshkovo".

Type of work: installation of an external lightning protection system (lightning-receiving part and down conductors).

Accessories:

Execution: The total amount of hot-dip galvanized steel conductor for 13 facilities in the facility was 21.5000 meters. A lightning protection mesh is laid along the roofs with a cell spacing of 5x5 m, 2 down conductors are mounted at the corners of buildings. Wall holders, intermediate connectors, holders for a flat roof with concrete, high-speed connecting terminals were used as fastening elements.

Solnechnogorsk plant "EUROPLAST"

Address of the object: Moscow region, Solnechnogorsk district, village. Radumlya.

Type of work: Designing a lightning protection system for an industrial building.

Accessories: manufactured by OBO Bettermann.

Choice of lightning protection system: Lightning protection of the entire building should be performed according to category III in the form of a lightning protection mesh made of hot-dip galvanized conductor Rd8 with a cell pitch of 12x12 m. Lay the lightning protection conductor over the roofing on holders for a soft roof made of plastic with concrete weighting. Provide additional protection for equipment at the lower level of the roof by installing a multiple lightning rod consisting of lightning rods. As a lightning rod, use a hot-dip galvanized steel rod Rd16 with a length of 2000 mm.

McDonald's building

Address of the object: Moscow region, Domodedovo, M4-Don highway

Type of work: Manufacturing and installation of external lightning protection system.

Accessories: manufactured by J. Propster.

Kit composition: lightning protection mesh made of conductor Rd8, 50 sq. mm, SGC; aluminum lightning rods Rd16 L=2000 mm; universal connectors Rd8-10/Rd8-10, SGC; intermediate connectors Rd8-10/Rd16, Al; wall holders Rd8-10, SGC; end terminals, SGC; plastic holders on a flat roof with a cover (with concrete) for a galvanized conductor Rd8; isolated rods d=16 L=500 mm.

Private cottage, Novorizhskoe highway

Address of the object: Moscow region, Novorizhskoe highway, cottage settlement

Type of work: manufacturing and installation of an external lightning protection system.

Accessories manufactured by Dehn.

Specification: Rd8 conductors made of galvanized steel, copper conductors Rd8, copper holders Rd8-10 (including ridge ones), universal connectors Rd8-10 made of galvanized steel, terminal holders Rd8-10 made of copper and stainless steel, copper seam terminal Rd8- 10, bimetal intermediate connectors Rd8-10/Rd8-10, tape and clamps for attaching the tape to the downspout made of copper.

Private house, Iksha

Address of the object: Moscow region, Iksha village

Type of work: Design and installation of external lightning protection, grounding and potential equalization systems.

Accessories: B-S-Technic, Citel.

External lightning protection: copper lightning rods, copper conductor with a total length of 250 m, roof and facade holders, connecting elements.

Internal lightning protection: Surge arrester DUT250VG-300/G TNC, manufactured by CITEL GmbH.

Grounding: ground rods made of galvanized steel Rd20 12 pcs. with ferrules, steel strip Fl30 with a total length of 65 m, cross connectors.

Private house, Yaroslavskoe shosse

Address of the object: Moscow region, Pushkinsky district, Yaroslavskoe shosse, cottage village

Type of work: Design and installation of an external lightning protection and grounding system.

Accessories manufactured by Dehn.

The composition of the lightning protection kit of the structure: conductor Rd8, 50 sq. mm, copper; pipe clamp Rd8-10; lightning rods Rd16 L=3000 mm, copper; ground rods Rd20 L=1500 mm, SGC; strip Fl30 25x4 (50 m), galvanized steel; arrester DUT250VG-300/G TNC, CITEL GmbH.

Territory "Noginsk-Technopark", production and warehouse building with office and amenity block

Address of the object: Moscow region, Noginsk district.

Type of work: production and installation of external lightning protection and grounding systems.

Accessories: J. Propster.

External lightning protection: On the flat roof of the protected building, a lightning protection mesh with a cell pitch of 10 x 10 m is laid. Anti-aircraft lamps are protected by installing lightning rods 2000 mm long and 16 mm in diameter in the amount of nine pieces on them.

Down conductors: Laid in the "pie" of the facades of the building in the amount of 16 pieces. For down conductors, a galvanized steel conductor in a PVC sheath with a diameter of 10 mm was used.

Grounding: Made in the form of a ring circuit with a horizontal ground electrode in the form of a galvanized strip 40x4 mm and deep grounding rods Rd20 with a length of L 2x1500 mm.

All objects

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Geography of thunderstorms

At the same time, about one and a half thousand thunderstorms operate on Earth, the average intensity of discharges is estimated at 100 lightning per second. Thunderstorms are unevenly distributed over the surface of the planet. There are approximately ten times less thunderstorms over the ocean than over the continents. About 78% of all lightning discharges are concentrated in the tropical and equatorial zone (from 30° north latitude to 30° south latitude). The maximum thunderstorm activity occurs in Central Africa. There are practically no thunderstorms in the polar regions of the Arctic and Antarctic and over the poles. The intensity of thunderstorms follows the sun: the maximum thunderstorms occur in the summer (in the middle latitudes) and in the daytime afternoon hours. The minimum recorded thunderstorms occur before sunrise. Thunderstorms are also affected by geographical features of the area: strong thunderstorm centers are located in the mountainous regions of the Himalayas and the Cordillera.

The average annual number of days with a thunderstorm in some cities of Russia:

City	Number of days with thunder
Arkhangelsk	20
Astrakhan	14
Barnaul	32
Blagoveshchensk	28
Bryansk	28
Vladivostok	13
Volgograd	21
Voronezh	26
Ekaterinburg	28
Irkutsk	15
Kazan	28
Kaliningrad	18
Krasnoyarsk	24
Moscow	24
Murmansk	4
Nizhny Novgorod	28
Novosibirsk	20
Omsk	27
Orenburg	28
Petropavlovsk-Kamchatsky	1
Rostov-on-Don	31
Samara	25
Saint Petersburg	16
Saratov	28
Sochi	50
Stavropol	26
Syktyvkar	25
Tomsk	24
Ufa	31
Khabarovsk	25
Khanty-Mansiysk	20
Chelyabinsk	24
Chita	27
Yuzhno-Sakhalinsk	7
Yakutsk	12

Development stages of a thundercloud

with uneven heating of the surface layer of air over a different underlying surface. For example, over the water surface and land due to differences in water and soil temperatures. Over large cities, the intensity of convection is much higher than in the vicinity of the city.
when warm air rises or is displaced by cold air at atmospheric fronts. Atmospheric convection at atmospheric fronts is much more intense and more frequent than during intramass convection. Often, frontal convection develops simultaneously with nimbostratus clouds and extensive precipitation, which masks the resulting cumulonimbus clouds.
when air rises in areas of mountain ranges. Even small elevations in the terrain lead to increased cloud formation (due to forced convection). High mountains create especially difficult conditions for the development of convection and almost always increase its frequency and intensity.

All thunderclouds, regardless of their type, go through successive stages of a cumulus cloud, a mature thundercloud stage, and a decay stage.

Thundercloud classification

In the 20th century, thunderstorms were classified according to the conditions of formation: intramass, frontal, or orographic. It is now more common to classify thunderstorms according to the characteristics of the thunderstorms themselves, and these characteristics are mainly dependent on the meteorological environment in which the thunderstorm develops.
The main necessary condition for the formation of thunderclouds is the state of instability of the atmosphere, which forms updrafts. Depending on the magnitude and power of such flows, thunderclouds of various types are formed.

single cell

Single-cell cumulonimbus (Cumulonimbus, Cb) clouds develop on days with weak winds in a low-gradient baric field. They are also called intramass or local. They consist of a convective cell with an ascending flow in its central part, they can reach lightning and hail intensity and quickly collapse with precipitation. The dimensions of such a cloud are: transverse - 5-20 km, vertical - 8-12 km, life expectancy - about 30 minutes, sometimes up to 1 hour. Serious weather changes after a thunderstorm do not occur.
Cloud formation begins with the appearance of a fair weather cumulus cloud (Cumulus humilis). Under favorable conditions, the resulting cumulus clouds grow rapidly both in the vertical and horizontal directions, while the updrafts are located almost throughout the volume of the cloud and increase from 5 m/s to 15-20 m/s. Downstreams are very weak. Ambient air actively penetrates into the cloud due to mixing at the boundary and top of the cloud. The cloud passes into the stage of medium cumulus (Cumulus mediocris). The smallest water drops formed as a result of condensation in such a cloud merge into larger ones, which are carried away by powerful upward flows. The cloud is still homogeneous, consists of water droplets held by an ascending flow - precipitation does not fall. In the upper part of the cloud, when water particles enter the zone of negative temperatures, the drops gradually begin to turn into ice crystals. The cloud becomes a powerful cumulus cloud (Cumulus congestus). The mixed composition of the cloud leads to the enlargement of cloud elements and the creation of conditions for precipitation and the formation of lightning discharges. Such a cloud is called a cumulonimbus (Cumulonimbus) or (in a particular case) a bald cumulonimbus (Cumulonimbus calvus). Vertical flows in it reach 25 m/s, and the level of the summit reaches a height of 7-8 km.
Evaporating precipitation particles cool the surrounding air, which leads to a further increase in downdrafts. At the stage of maturity, both ascending and descending air currents are present in the cloud at the same time.
At the decay stage, the cloud is dominated by downdrafts, which gradually cover the entire cloud.

Multicell cluster thunderstorms

Multicell line thunderstorms (squall lines)

Multicell line thunderstorms are a line of thunderstorms with a long, well-developed gust front on the front front line. The squall line may be continuous or contain gaps. The approaching multicell line looks like a dark wall of clouds, usually covering the horizon from the western side (in the northern hemisphere). A large number of closely spaced ascending/descending air currents allows us to qualify this complex of thunderstorms as a multi-cell thunderstorm, although its thunderstorm structure differs sharply from a multi-cell cluster thunderstorm. Squall lines can produce large hail (greater than 2 cm in diameter) and intense showers, but they are known to create strong downdrafts and shear winds that are dangerous to aviation. The squall line is similar in properties to a cold front, but is a local result of thunderstorm activity. Often a squall line occurs ahead of a cold front. On radar images, this system resembles a curved bow (bow echo). This phenomenon is typical for North America, in Europe and the European territory of Russia it is observed less frequently.

Supercell thunderstorms

A supercell is the most highly organized thundercloud. Supercell clouds are relatively rare, but pose the greatest threat to human health and life and property. A supercell cloud is similar to a single cell cloud in that both have the same updraft zone. The difference lies in the size of the supercell: a diameter of about 50 km, a height of 10-15 km (often the upper boundary penetrates into the stratosphere) with a single semicircular anvil. The speed of the ascending flow in a supercell cloud is much higher than in other types of thunderclouds: up to 40-60 m/s. The main feature that distinguishes a supercell cloud from other types of clouds is the presence of rotation. A rotating updraft in a supercell cloud (called a mesocyclone in radar terminology) creates extreme weather events, such as large hail (2-5 cm in diameter, sometimes more), squalls with speeds up to 40 m/s and strong destructive tornadoes . Environmental conditions are a major factor in the formation of a supercell cloud. A very strong convective instability of the air is needed. The air temperature near the ground (before a thunderstorm) should be +27 ... +30 and higher, but the main necessary condition is the wind of a variable direction, which causes rotation. Such conditions are achieved with wind shear in the middle troposphere. Precipitation formed in the updraft is carried along the upper level of the cloud by a strong flow into the downdraft zone. Thus, the zones of the ascending and descending flows are separated in space, which ensures the life of the cloud for a long period of time. There is usually light rain at the leading edge of a supercell cloud. Heavy rainfall occurs near the updraft zone, while the heaviest precipitation and large hail fall to the northeast of the main updraft zone. The most dangerous conditions occur close to the main updraft area (usually displaced to the rear of the thunderstorm).

Physical characteristics of thunderclouds

Airborne and radar studies show that a single thunderstorm cell typically reaches a height of about 8-10 km and lives for about 30 minutes. An isolated thunderstorm usually consists of several cells in various stages of development and lasts on the order of an hour. Large thunderstorms can reach tens of kilometers in diameter, their peak can reach heights of over 18 km, and they can last for many hours.

Upstream and downstream

Flurries

In some thunderstorms, intense downdrafts develop, creating destructive winds on the surface of the earth. Depending on the size, such downdrafts are called squalls or microsqualls. A squall with a diameter of more than 4 km can create winds up to 60 m/s. Microsqualls are smaller, but create wind speeds up to 75 m/s. If the thunderstorm that generates the squall is formed from sufficiently warm and moist air, then the microsquall will be accompanied by intense rain showers. However, if the thunderstorm is formed from dry air, the precipitation may evaporate during the fall (airborne precipitation bands or virga) and the microsquall will be dry. Downdrafts are a serious hazard to aircraft, especially during takeoff or landing, as they create wind near the ground with sudden changes in speed and direction.

Vertical development

Turbulence

An aircraft flying through a thundercloud (it is forbidden to fly into cumulonimbus clouds) usually gets into a turbulence that throws the plane up, down and sideways under the influence of turbulent cloud flows. Atmospheric turbulence creates a feeling of discomfort for the aircraft crew and passengers and causes undesirable stresses on the aircraft. Turbulence is measured in different units, but more often it is defined in units of g - free fall acceleration (1g = 9.8 m/s 2). A flurry of one g creates turbulence that is dangerous for aircraft. In the upper part of intense thunderstorms, vertical accelerations up to three g were registered.

Movement

The speed and movement of a thundercloud depends on the direction of the wind, first of all, the interaction of the ascending and descending flows of the cloud with the carrier air flows in the middle layers of the atmosphere in which a thunderstorm develops. The speed of movement of an isolated thunderstorm is usually on the order of 20 km/h, but some thunderstorms move much faster. In extreme situations, a thundercloud can move at speeds of 65-80 km / h - during the passage of active cold fronts. In most thunderstorms, as old thunderstorm cells dissipate, new thunderstorm cells emerge in succession. With a weak wind, an individual cell can travel a very short distance during its life, less than two kilometers; however, in larger thunderstorms, new cells are triggered by the downdraft flowing out of the mature cell, giving the impression of rapid movement that does not always match the direction of the wind. In large multicell thunderstorms, there is a pattern where a new cell forms to the right of the carrier airflow in the northern hemisphere and to the left of the carrier airflow in the southern hemisphere.

Energy

The energy that powers a thunderstorm is the latent heat released when water vapor condenses and forms cloud droplets. For every gram of water that condenses in the atmosphere, approximately 600 calories of heat are released. When the water droplets freeze at the top of the cloud, about 80 more calories per gram are released. The released latent thermal energy is partially converted into the kinetic energy of the upward flow. A rough estimate of the total energy of a thunderstorm can be made from the total amount of water that has precipitated from the cloud. Typical is an energy of the order of 100 million kilowatt-hours, which is roughly equivalent to a nuclear charge of 20 kilotons (although this energy is released in a much larger volume of space and over a much longer time). Large multi-cell thunderstorms can have tens or hundreds of times more energy.

Weather phenomena under thunderstorms

Downdrafts and squall fronts

Downdrafts in thunderstorms occur at altitudes where the air temperature is lower than the temperature in the surrounding space, and this stream becomes even colder when ice particles of precipitation begin to melt in it and cloud drops evaporate. The air in the downdraft is not only denser than the surrounding air, but it also carries a different horizontal angular momentum than the surrounding air. If a downdraft occurs, for example, at a height of 10 km, then it will reach the earth's surface with a horizontal speed that is noticeably greater than the wind speed near the earth. Near the ground, this air is carried forward before a thunderstorm at a speed greater than the speed of the entire cloud. That is why an observer on the ground will feel the approach of a thunderstorm along a stream of cold air even before the thundercloud is overhead. The downdraft propagating along the ground forms a zone with a depth of 500 meters to 2 km with a distinct difference between the cold air of the stream and the warm, moist air from which the thunderstorm is formed. The passage of such a squall front is easily determined by the increase in wind and a sudden drop in temperature. In five minutes, the air temperature can drop by 5 °C or more. The squall forms a characteristic squall gate with a horizontal axis, a sharp drop in temperature, and a change in wind direction.

Tornadoes

A tornado is a strong small-scale eddy beneath thunderclouds with an approximately vertical but often curved axis. From the periphery to the center of the tornado, there is a pressure drop of 100-200 hPa. The wind speed in tornadoes can exceed 100 m/s, theoretically it can reach the speed of sound. In Russia, tornadoes occur relatively rarely. The highest frequency of tornadoes occurs in the south of the European part of Russia.

Livni

In small thunderstorms, the five-minute peak of intense precipitation can exceed 120 mm/h, but the rest of the rain has an order of magnitude lower intensity. An average thunderstorm produces about 2,000 cubic meters of rain, but a large thunderstorm can produce ten times as much. Large organized thunderstorms associated with mesoscale convective systems can produce 10 to 1000 million cubic meters of precipitation.

Electrical structure of a thundercloud

electrification mechanism

Many mechanisms have been proposed to explain the formation of the electrical structure of a thundercloud, and this area of science is still an area of active research. The main hypothesis is based on the fact that if larger and heavier cloud particles are predominantly negatively charged, and lighter small particles carry a positive charge, then the spatial separation of space charges occurs due to the fact that large particles fall at a higher speed than small cloud components. This mechanism is generally consistent with laboratory experiments, which show a strong charge transfer when particles of ice pellets (grain - porous particles of frozen water droplets) or hail particles interact with ice crystals in the presence of supercooled water droplets. The sign and magnitude of the charge transferred during the contacts depend on the temperature of the surrounding air and the water content of the cloud, but also on the size of the ice crystals, the velocity of the collision, and other factors. It is also possible the action of other mechanisms of electrification. When the magnitude of the volume electric charge accumulated in the cloud becomes large enough, a lightning discharge occurs between the areas charged with the opposite sign. A discharge can also occur between a cloud and the ground, a cloud and a neutral atmosphere, a cloud and the ionosphere. In a typical thunderstorm, two thirds to 100 percent of the discharges are intracloud discharges, intercloud discharges, or cloud-to-air discharges. The rest are cloud-to-ground discharges. In recent years, it has become clear that lightning can be artificially initiated in a cloud, which under normal conditions does not pass into the thunderstorm stage. In clouds that have zones of electrization and create electric fields, lightning can be initiated by mountains, high-rise buildings, aircraft or rockets that are in the zone of strong electric fields.

Precautions during a thunderstorm

Precautions are due to the fact that lightning strikes mainly higher objects. This is because the electrical discharge follows the path of least resistance, that is, the shorter path.

During a thunderstorm, do not:

be near power lines;
hide from the rain under trees (especially under tall or lonely ones);
swim in water bodies (since the swimmer's head protrudes from the water, in addition, water, due to the substances dissolved in it, has good electrical conductivity);
to be in an open space, in an “open field”, since in this case a person protrudes significantly above the surface;
climb up hills, including on the roofs of houses;
use metal objects;
be near windows;
ride a bike and motorcycle;
use a mobile phone (electromagnetic waves have good electrical conductivity).

Failure to follow these rules often results in death or burns and serious injury.