Be specific about lightning introduction

Lightning

Lightning

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1. Natural phenomenon

Storm clouds usually produce electric charges , the bottom layer is negative electricity, the top layer is positive electricity, and positive electricity is also generated on the ground, which moves with the clouds like a shadow. Positive and negative charges attract each other, but air is not a good conductor. The positive electricity rushes to the tops of trees, hills, tall buildings and even the human body, trying to meet the clouds with negative electricity; the branch-like tentacles of negative electricity extend downward, getting closer to the ground as they extend downward. Finally, the yin and yang charges finally overcome the air barrier and connect. A huge electric current surges from the ground to the cloud along a conductive airway, producing a bright and dazzling flash of light. A bolt of lightning may be only a few hundred kilometers long, but can be up to several thousand meters long.

The temperature of lightning ranges from 17,000 to 28,000 degrees Celsius, which is equal to 3 to 5 times the surface temperature of the sun. The extreme heat of lightning causes the air in its path to expand dramatically. The air moves quickly, so it forms waves and makes sound. If the lightning is close, you will hear a sharp crackle; if it is far away, you will hear a rumble. You can start the stopwatch after seeing lightning, stop it when you hear thunder, and then divide the number of seconds by 3 to roughly know how many kilometers away from you the lightning is.

Shapes of lightning

Line lightning, ribbon lightning, ball lightning, and bead lightning.

What we commonly see is linear lightning, which is like a branch with many branches, winding and twisting. Ribbon lightning is similar to linear lightning, except that the bright channel is wider and looks like a brighter band. Ball lightning generally occurs after linear lightning. It is a fireball with a diameter of about 20 centimeters, emitting red or orange light, and occasionally a beautiful green color, which usually lasts for a few seconds. The fireball drifts in the air with the wind, likes to slide along the edges of objects, and can also enter the room through gaps. When it is about to disappear, it will make a deafening explosion sound.

Among all kinds of lightning, the rarest is bead lightning, which most people in the world have never seen. This kind of lightning is like a string of luminous pearls extending from the clouds to the ground (on May 8, 1916, a chain of pearl-like lightning occurred over a clock tower in Dresden, Germany, and was recorded. People First, a linear lightning was seen extending down from the clouds. Later, people saw that the linear lightning channel widened and its color changed from white to yellow. Soon the lightning channel gradually darkened, but the entire channel was not uniform at the same time. It darkens, so the bright channel becomes a string of pearl-like bright spots, hanging down from the clouds, beautiful and moving. People estimate that there are 32 bright beads, each with a diameter of 5 meters. After that, the bright beads gradually shrink and become round in shape. ; Finally, the brightness becomes darker and darker, and then it is completely extinguished.) Since the occurrence of bead-like lightning is very rare and the duration is very short, people have rarely studied the cause of this kind of lightning, and the reason for its formation is still unclear. .

Types of lightning

Ordinary lightning with zigzag and forked branches is called dendrite lightning. When the channel of dendrite lightning is blown to both sides by the wind so that there appear to be several parallel lightning bolts, it is called ribbon lightning. If the two branches of lightning appear to reach the ground at the same time, it is called forked lightning.

When lightning flashes between yin and yang charges in the cloud, causing the entire sky to light up, it is called patch lightning.

Lightning that does not reach the ground, that is, lightning within the same cloud layer or between two cloud layers, is called inter-cloud lightning. Sometimes this kind of rampant lightning will travel a long distance and land on the ground many kilometers away from the storm. This is called a "bolt from the blue."

The electrical action of lightning sometimes creates a halo-like red light around tall, pointed objects. Usually on a stormy sea, a fiery red light can be seen around the mast of a ship. People borrowed the name of the patron saint of sailors and called this lightning "St. Elmo's Fire."

Super lightning

Super lightning refers to rare lightning that is more than 100 times more powerful than ordinary lightning. Ordinary lightning generates about 1 billion watts of electricity, while super lightning generates at least 100 billion watts, and may even reach trillions to 10,000 billion watts.

Bell Island in Newfoundland was apparently struck by a super lightning strike in 1978. Even houses 13 kilometers away were rattled and blue flames spewed out of doors and windows throughout the countryside.

Time of Attack

As you read this article, approximately 1,800 lightning strikes are underway around the world. They emit approximately 600 lightning strikes per second, 100 of which strike Earth.

Lightning can turn part of the nitrogen in the air into nitrogen compounds, which can be washed down to the ground by rain. Every hectare on Earth receives a few kilograms of this free fertilizer from the sky over the course of a year.

Kampala, the capital of Uganda, and the Indonesian island of Java are the places most vulnerable to lightning strikes. According to statistics, lightning occurs on Java Island 300 days a year.

The most violent lightning in history was the one that struck a hut near Umtari in rural Zimbabwe in 1975, killing 21 people.

Who is attacked

More than 2/3 of lightning victims are attacked outdoors. Two out of every three of them survived. Of those killed by lightning, 85% were male, mostly between the ages of 10 and 35. Most of the dead were sheltered from thunderstorms under trees.

Sullivan may be the champion of being struck by lightning. He is a retired forest ranger who has been struck by lightning seven times. Lightning has singed his eyebrows, burned his hair, burned his shoulders, ripped off his shoes, and even thrown him out of a car. He said lightly: "Lightning always finds a way to find me."

Instructions for preventing lightning strikes

(1) Don't stand under a big tree.

(2) Don’t let yourself become the tallest object around.

(3) Put down all metal objects. Don't ride a bicycle.

(4) Do not use telephones, water pipes or electrical appliances that require plugging.

(5) Stay away from doors, windows, heaters, stoves, and chimneys.

(6) The safest place in the house is in the center of the largest room downstairs.

P.S. Finally, there is one thing you can take comfort in: By the time you see the lightning, it will no longer be able to hit you.

The formation of black lightning baffles scientists. For a long time, people have only had blue and white lightning in their minds. This is a natural phenomenon of atmospheric discharge in the sky, which is usually accompanied by a dazzling light! And I have never seen "black lightning" that does not glow. However, scientists have indeed proven the existence of "black lightning" through long-term observation and research.

On June 23, 1974, the former Soviet astronomer Chernov saw a "black lightning" in the city of Zabalozh: it started as a strong ball lightning, and then followed by Flying past was a black mass that looked like mist-like condensation. Research and analysis show that black lightning is produced by molecular aerogel aggregates, and these aggregates are heated, charged substances that can easily explode or transform into ball lightning, which is extremely dangerous.

According to observation and research, black lightning is generally not easy to appear near the ground. If it does appear, it is more likely to hit trees, masts, houses and other metals. It usually appears in the shape of knobs or mud balls. At first glance, Like a ball of dirty things, it is easy to be ignored by people, but it itself contains a large amount of energy. Therefore, it is the most dangerous and harmful type among the "Lightning Clan". In particular, black lightning is small and difficult to capture by radar; moreover, it favors metal objects; therefore, it is called "airborne minefield" by pilots. If the aircraft touches black lightning during flight, the consequences will be disastrous. Whenever black lightning is close to the ground, it is easy to be mistaken for a bird or something else, and it is not easy to arouse people's vigilance and attention; if it is hit with a stick, it will explode quickly, causing serious damage. The danger of people being shattered to pieces. In addition, black lightning is similar to ball lightning. General lightning protection facilities such as lightning rods, lightning balls, lightning protection nets, etc. cannot protect black lightning; therefore, it often reaches oil storage tanks and storage tanks with extremely strict lightning protection measures very smoothly. Near gas tanks, transformers, and explosive depots. Don't get close to it at this moment. You should stay away and put your personal safety first.

The reason for the formation of lightning

Airflow in thunderclouds will generate static electricity due to the friction and decomposition of water molecules. There are two types of electricity. One is positively charged particles with positively charged particles. Electricity, a kind of negative electricity with negatively charged particles. Positive and negative charges will attract each other, just like magnets. Positive charges are at the upper end of the cloud, and negative charges at the lower end of the cloud attract positive charges on the ground. Between the cloud and the ground The air in the air is an insulator, which will prevent the electric current of the two poles from passing through. When the electric charge in the thunderstorm cloud and the electric charge on the ground become strong enough, the two parts of the electric charge will break through the obstruction of the air and come into contact to form a strong electric current. The positive charge and The negative charges come into contact. When these opposite charges meet, neutralization (discharge) will occur. The intense charge neutralization will release a large amount of light and heat, and the released light will form [lightning].

Most lightning is connected twice. The first time is called a leader flash connection. It is an invisible air called a leader, which goes down to a place close to the ground. This charged air is like a The wire creates a guide path for the second current. The moment the leader approaches the ground, a tieback current jumps up along this guide path. The flash produced by this tieback is the lightning we usually see.

Causes of Thunder

It is now known that a large amount of light and heat will be emitted during charge neutralization. The instantaneous release of a large amount of heat will heat the surrounding air to a high temperature of 30,000 degrees Celsius. Strong When an electric current passes through the air, it causes the air along the way to suddenly expand, and at the same time pushes the surrounding air, causing the air to vibrate violently. The sound produced at this time is [thunder]. (Don't forget to tell the baby that thunder and lightning are Happening at the same time, because the speed of light is much faster than the speed of sound, we always see lightning first and then hear thunder.)

If lightning falls close by, what we hear is a deafening boom. Sound. If lightning falls far away, what we hear is rumbling thunder. This is because the echo is emitted after sound waves are refracted by the atmosphere and reflected by ground objects.

Necessary for the occurrence of thunder and lightning Conditions

1. The air must be very humid;

2. The clouds must be very large;

Areas with dry weather are generally not prone to thunder and lightning.

The process of lightning

If we add a very high voltage between two electrodes and slowly bring them closer. When two electrodes come close to a certain distance, an electric spark will appear between them. This is the so-called "arc discharge" phenomenon.

The lightning generated by thunderclouds is very similar to the arc discharge mentioned above, except that the lightning is fleeting, but the sparks between the electrodes can exist for a long time. Because the high voltage between the two electrodes can be artificially maintained for a long time, but the charge in the thundercloud is difficult to replenish immediately after being discharged. When the accumulated charge reaches a certain amount, a strong electric field is formed between different parts of the cloud or between the cloud and the ground. The electric field intensity can reach several thousand volts/cm on average, and can be as high as 10,000 volts/cm in local areas. Such a strong electric field is enough to penetrate the atmosphere inside and outside the cloud, thus stimulating dazzling flashes of light between the cloud and the ground or between different parts of the cloud and between different cloud masses. This is what people often call lightning.

The process of lightning seen by the naked eye is very complicated. When a thundercloud moves somewhere, the middle and lower part of the cloud is a strong negative charge center, and the underlying surface opposite the cloud base becomes a positive charge center, forming a strong electric field between the cloud base and the ground. When the electric charge accumulates more and more and the electric field becomes stronger and stronger, a column of air where the atmosphere is strongly ionized first appears at the cloud base, which is called a step leader. This ionized gas column extends step by step toward the ground. The leader of each step is a dim light column with a diameter of about 5 meters, a length of 50 meters, and a current of about 100 amps. It extends step by step at an average speed of about 150,000 meters/second. Towards the ground, when it is about 5-50 meters away from the ground, the ground suddenly strikes back upwards. The path of the rebound is from the ground to the bottom of the cloud, along the ionization channel opened up by the above-mentioned step leader. The response flew from the ground to the cloud base at a higher speed of 50,000 kilometers per second, emitting an extremely bright beam of light that lasted 40 microseconds and passed through more than 10,000 amperes. This was the first lightning strike. A few seconds later, a dim beam of light emerged from the cloud, carrying a huge electric current, and flew towards the ground along the path of the first lightning strike. It was called a direct leader. When it was about 5-50 meters away from the ground, the ground struck back upwards, and then struck back upwards. Forming an extremely bright beam of light, this was the second flash strike. Then there were third and fourth blitzes similar to the second time. A lightning process usually consists of 3-4 lightning strikes. A lightning process lasts about 0.25 seconds. During this short period of time, a huge amount of electrical energy is released in a narrow lightning channel, resulting in a strong explosion, a shock wave, and then a sound wave that spreads around. This is thunder or "thunder" thunder".

The structure of lightning

Linear lightning has been studied in more detail. We will use it as an example to describe the structure of lightning. Lightning is a pulse-like discharge phenomenon in the atmosphere. A lightning bolt consists of multiple discharge pulses with short intervals between them, only a few hundredths of a second. The pulses come one after the other, with subsequent pulses following the path of the first pulse.

It has now been clearly studied that each discharge pulse consists of a "leader" and a "rebound". Before the first discharge pulse erupts, there is a preparation stage - the "step leader" discharge process: driven by a strong electric field, The free charges in the cloud move quickly towards the ground. During their movement, the electrons collide with air molecules, causing the air to be slightly ionized and emit a faint light. The leader of the first discharge pulse propagates downward step by step. A glowing tongue. At first, this tongue of light was only a dozen meters long. After a few thousandths of a second or less, the tongue of light disappeared; then a longer tongue of light appeared on the same channel ( About 30 meters long), it disappears in an instant; then a longer tongue of light appears... The tongue of light adopts a "nibbling" method and approaches the ground step by step. After many discharges and disappearances, the tongue of light finally arrives. The ground. Because the leader of this first discharge pulse propagates from the cloud to the ground step by step, it is called a "step leader". On the path where the light tongue travels, the air has been strongly ionized, and its conductivity is high. The capacity is greatly increased. The process of continuous air ionization only occurs in a very narrow channel, so the current intensity is very high.

When the first leader, the ladder leader, reaches the ground, it immediately passes through the ground. The highly ionized air channel flows a large amount of charge into the cloud. This current is so strong that the air channel is burned brightly, and a winding and slender light column appears. This stage is called the "return" stage. It is called the "main discharge" stage. The ladder leader plus the first return stroke constitute the entire process of the first pulse discharge, which lasts only one hundredth of a second.

740) this.width. =740" border=undefined> After the first pulse discharge process ends, only after a very short period of time (four hundredths of a second), the second pulse discharge process occurs. The second pulse also starts from the leader and ends with the counterattack. However, since after the first pulse discharge, "the ice has been broken and the route has been opened," the leader of the second pulse no longer goes downward step by step, but directly reaches the ground from the cloud. This kind of leader is called "direct channel leader". After the direct channel leader reaches the ground, it takes about a few thousandths of a second for a second counterattack to occur, ending the second pulse discharge process. Then the third and fourth happened... . Directly channel the leader and return attack to complete multiple pulse discharge processes. Since each pulse discharge consumes a large amount of the charge accumulated in the thundercloud, the subsequent main discharge process becomes weaker and weaker. Until the charge reserve in the thundercloud is exhausted, the pulse discharge can stop, thereby ending a lightning strike. process.

The cause of lightning

The atmospheric electric field during a thunderstorm is significantly different from that on a sunny day. The reason for this difference is the accumulation of electric charges in thunderclouds and the formation of thunderclouds. polarity, resulting in lightning causing huge changes in the atmospheric electric field. But where does the electricity in thunderclouds come from? That is to say, what physical processes in thunderclouds lead to its electrification? Why can thunderclouds accumulate so much charge and form a regular distribution? This section will answer the question these questions. We have already mentioned before that the macroscopic process of thundercloud formation and the microphysical processes occurring in thunderclouds are closely related to the electrification of clouds. Scientists have conducted a large number of observations and experiments on the electrification mechanism of thunderclouds and the regular distribution of charges, accumulated a lot of data and proposed various explanations. Some arguments are still controversial today. To sum up, the main electrification mechanisms of clouds are as follows:

A. "Ion flow" hypothesis in the initial stage of convective clouds

There are always a large number of positive ions in the atmosphere And negative ions, on the water droplets in the cloud, the charge distribution is uneven: the outermost molecules are negatively charged, the inner layer is positively charged, and the potential difference between the inner layer and the outer layer is about 0.25 volts higher. In order to balance this potential difference, water droplets must "preferentially" absorb negative ions in the atmosphere, so that the water droplets gradually become negatively charged. When convection develops, lighter positive ions are gradually carried to the upper part of the cloud by the updraft; and Because the negatively charged cloud droplets are relatively heavy, they remain in the lower part, causing the separation of positive and negative charges.

B. Charge accumulation in cold clouds

When convection develops to a certain stage, When the cloud body reaches a height above the 0°C layer, there are supercooled water droplets, graupel particles, and ice crystals in the cloud. This type of cloud is composed of water vapor condensates of different phases and has a temperature lower than 0°C, and is called a cold cloud. The charge formation and accumulation processes of cold clouds are as follows:

a. The friction and collision of ice crystals and graupel particles generate electricity

Graupel particles are composed of frozen water droplets, which are white or milky white. The structure is relatively brittle. Because supercooled water droplets often collide with it and release latent heat, its temperature is generally higher than that of ice crystals. Ice crystals contain a certain amount of free ions (OH- or OH+), and the number of ions varies. It increases as the temperature increases. Due to the temperature difference between the graupel particles and the ice crystal, there must be more free ions at the high temperature end than at the low temperature end, so when the ions migrate from the high temperature end to the low temperature end, the lighter positively charged hydrogen must move. The ions are faster, while the negatively charged heavier hydroxide ions (OH-) are slower. Therefore, an excess of H+ ions occurs at the cold end within a certain period of time, causing the high temperature end to be negative and the low temperature end to be negative. Positive electrical polarization.

When ice crystals come into contact with graupel particles and then separate, the higher-temperature graupel particles become negatively charged, while the cooler ice crystals become positively charged. Under the action of gravity and updrafts, the lighter positively charged ice crystals are concentrated in the upper part of the cloud, while the heavier negatively charged ice crystals stay in the lower part of the cloud, thus causing the upper part of the cold cloud to be positively charged while the lower part is Negatively charged.

b. Supercooled water droplets collide with graupel grains to freeze and generate electricity

There are many water droplets in clouds that do not freeze when the temperature is lower than 0°C. Such water droplets are called supercooled water droplets. . Supercooled water droplets are unstable and will freeze into ice particles as soon as they are shaken slightly. When supercooled water droplets collide with graupel particles, they freeze immediately, which is called impact freezing. When impact freezing occurs, the outside of the supercooled water droplet immediately freezes into an ice shell, but the inside of the droplet remains temporarily liquid, and because the latent heat released by the external freezing is transferred to the inside, the temperature of the liquid supercooled water inside is higher than that of the ice shell outside. high. The difference in temperature causes the frozen supercooled water droplets to become positively charged on the outside and negatively charged on the inside. When freezing occurs inside, the cloud droplets expand and split, and the outer skin breaks into many positively charged small ice fragments, which fly to the upper part of the cloud with the airflow. The negatively charged core of the frozen droplets is attached to the heavier graupel particles. The graupel particles are negatively charged and stay in the middle and lower parts of the cloud.

c. Water droplets are electrified because they contain thin salt content

In addition to the two electrification mechanisms of cold clouds mentioned above, some people have also proposed that water droplets in the atmosphere contain thin salt content. The electrification mechanism produced. When cloud droplets freeze, the ice's crystal lattice accommodates negative chloride ions (Cl-) but excludes positive sodium ions (Na+). Therefore, the frozen part of the water droplet is negatively charged, while the unfrozen outer surface is positively charged (when the water droplet freezes, it proceeds from the inside out). As the graupel grains formed by frozen water droplets fall, they throw off the water on the surface that has not had time to freeze, forming many positively charged small cloud droplets, while the frozen core part is negatively charged. Due to the sorting effect of gravity and airflow, the positively charged droplets are carried to the upper part of the cloud, while the negatively charged graupel particles stay in the middle and lower parts of the cloud.

d. Charge accumulation in warm clouds

The above describes some of the main mechanisms of electrification in cold clouds. In the tropics, there are some clouds whose entire cloud body is located above 0°C and therefore contains only water droplets but no solid water particles. Such clouds are called warm clouds or "water clouds." Warm clouds can also cause thunder and lightning. In thunderstorm clouds in mid-latitudes, the part of the cloud body below the 0°C isotherm is the warm zone of the cloud. Electrification processes also occur in the warm regions of clouds.

In the development process of thunderstorm clouds, the various mechanisms mentioned above may work respectively at different stages of development. However, the most important electrification mechanism is caused by the freezing of water droplets. A large number of observational facts show that clouds develop into thunderclouds only when the cloud top exhibits a fibrous strand structure. Aircraft observations also found that there are a large number of cloud particles mainly composed of ice, snow crystals and graupel particles in thunderclouds, and the accumulation of a large amount of charge, that is, the rapid electrification mechanism of thunderstorm clouds, must rely on collision, freezing and friction during the growth of graupel particles. Wait for it to happen.

Weird-shaped lightning

There are several shapes of lightning: the most common ones are linear (or dendritic) lightning and sheet lightning. Ball lightning is a very rare kind of lightning. shape. If distinguished carefully, shapes such as ribbon lightning, bead lightning, and rocket lightning can also be distinguished. Line lightning or dendrite lightning is a lightning shape that people often see. It has dazzling light and very thin light. The entire lightning looks like branches hanging horizontally or downwards, or like a river with many tributaries on the map.

The difference between linear lightning and other discharges is that it has a particularly large current intensity, which can reach tens of thousands of amperes on average and up to 200,000 amperes in a few cases. Such a high current intensity. It can destroy and shake large trees and sometimes injure people. When it comes into contact with buildings, it often causes "lightning strikes" and causes fires. Linear lightning is mostly cloud-to-ground discharge.

Sheet lightning is also a relatively common lightning shape. It looks like a flash of light on the cloud surface. This kind of lightning may be the return light of invisible spark discharge behind the cloud, or the diffuse light caused by the lightning in the cloud being blocked by cloud droplets, or it may be a cluster or flash-like independent discharge phenomenon that appears in the upper part of the cloud. . Sheet lightning often occurs when clouds have weakened and precipitation has ceased. It is a weak discharge phenomenon, most of which are discharges in clouds.

Although ball lightning is a very rare shape of lightning, it is the most eye-catching. It looks like a ball of fire, sometimes like a glowing blooming "hydrangea" chrysanthemum. It is about the size of a human head, and occasionally has a diameter of several meters or even dozens of meters. Sometimes ball lightning moves slowly through the air, and sometimes it hangs completely motionless. Sometimes it emits white light, sometimes it emits pink light like a shooting star. Ball lightning "likes" to drill holes. Sometimes, it can get into the house through chimneys, windows, and door cracks, circle around the house, and then slip away. Ball lightning sometimes makes a "hissing" sound and then disappears with a muffled sound; sometimes it only makes a weak crackling sound and disappears imperceptibly. After the ball lightning disappears, some smelly smoke may be left in the air, a bit like ozone. The life history of ball lightning is short, lasting from seconds to minutes.

Ribbon lightning.

It consists of several consecutive discharges. Between each lightning strike, the lightning path moves due to the influence of the wind, causing the individual lightning strikes to approach each other and form a strip. The width of the strip is approximately 10 meters. If this type of lightning strikes a house, it can instantly cause widespread fires.

Beaded lightning looks like a connected line of luminous points sliding on the cloud curtain or passing through the clouds to the ground. It also looks like a shining pearl necklace. Some people think that bead lightning seems to be a transitional form from linear lightning to ball lightning. Bead lightning often follows linear lightning with almost no time interval.

Rocket lightning discharges much slower than other types of lightning. It takes 1-1.5 seconds to complete the discharge. Its activity can be easily followed with the naked eye.

People can observe various shapes of lightning with their own eyes. However, to carefully observe lightning, it is best to take photos. High-speed cameras can not only record the shape of lightning, but also observe the development process of lightning. Using some special cameras (such as mobile cameras), the structure of lightning can also be studied.