How are thunder and lightning produced (formation process)?

lightning)

shandian

1 p > 1. Natural phenomena

Storm clouds usually generate charges, with negative charges at the bottom and positive charges at the top, and they also generate positive charges on the ground, moving with the clouds. Positive and negative charges attract each other, but air is not a good conductor. The positive electricity rushes to the top of trees, hills, tall buildings and even above the human body, trying to meet the clouds with negative electricity; Dendritic tentacles of negative charge extend downward, and the more they extend downward, the closer they get to the ground. Finally, the negative and positive charges finally overcome the air barrier and connect. A huge current rushes from the ground to the clouds along a conductive airway, producing a bright flash. The length of a lightning bolt may be only a few hundred kilometers, but it can be as long as several kilometers.

The temperature of lightning varies from 17, degrees Celsius to 28, degrees Celsius, which is 3-5 times the surface temperature of the sun. The extreme heat of lightning caused the air along the way to expand violently. Air moves quickly, so it forms waves and makes sounds. When lightning is close, what you hear is a sharp crack; If the distance is far, what you hear is rumbling. You can start the stopwatch after you see the lightning, press it to stop when you hear the thunder, and then divide the number of seconds by 3, so you can roughly know how many kilometers the lightning is from you.

types of lightning

ordinary lightning with twists and turns is called dendritic lightning. If the passage of dendritic lightning is blown to both sides by the wind, so that there seem to be several parallel lightning, it is called banded lightning. If two branches of lightning seem to reach the ground at the same time, they are called forked lightning.

When lightning flashes between negative and positive charges in the cloud, which makes the sky in the whole area bright, it is called sheet lightning.

lightning that does not reach the ground, that is, lightning in the same cloud or between two clouds, is called cloud-to-cloud lightning. Sometimes this kind of 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 electric action of lightning sometimes forms a halo-like red light around tall and sharp objects. Usually in a stormy sea, a fiery red light can be seen around the mast of a ship, so people borrow the name of the patron saint of sailors and call this lightning "the fire of San Elmo".

Super lightning

Super lightning refers to rare lightning that is more than 1 times more powerful than ordinary lightning. The electricity generated by ordinary lightning is about 1 billion watts, while the electricity generated by super lightning is at least 1 billion watts, and may even reach trillions to 1 trillion watts.

Clock Island in Newfoundland was obviously hit by a super lightning in 1978, and even houses 13 kilometers away were rattled, and blue flames were sprayed from the doors and windows of the whole village.

Time of the attack

As you read this article, there are about 1,8 lightning exchanges going on around the world. They emit about 6 flashes of lightning every second, 1 of which hit the earth.

lightning can change a part of nitrogen in the air into nitrogen compounds, which can be washed down to the ground by rain. In a year, every hectare of land on the earth can get a few kilograms of this free fertilizer from high altitude.

Kampala, the capital of Uganda, and Java, Indonesia, are the most vulnerable places to lightning. According to statistics, there were 3 days of lightning in Java one year. The most violent lightning in history was the one that struck a small house near Umtari in rural Zimbabwe in 1975, when 21 people were killed.

Who was attacked

More than two-thirds of lightning victims were attacked outdoors. Two of every three of them survived. Among the people killed by lightning, 85% were men, mostly between the ages of 1 and 35. Most of the dead were protected from lightning and rain under trees.

Sullivan may be the champion who was struck by lightning. He is a retired forest manager who was struck by lightning seven times. Lightning once scorched his eyebrows, burned his hair, burned his shoulders, ripped off his shoes and even threw him out of the car. He said airily, "Lightning always finds me."

precautions against lightning

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

(2) Don't make yourself the tallest object around.

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

(4) Don't use telephones, water pipes or electrical appliances that need to be plugged in.

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

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

p.s. Finally, there is one consolation: when you see lightning, it can't hit you.

The formation of black lightning is beyond scientists' explanation. For a long time, people's minds only have blue and white lightning, which is a natural phenomenon of atmospheric discharge in the air, usually accompanied by dazzling light! I have never seen a "black lightning" that doesn't shine. However, scientists have indeed proved the existence of "black lightning" through long-term observation and research.

On June 23, 1974, the astronomer Chernoff of the former Soviet Union once saw a "black lightning" in Zabarozh: at first, it was a strong ball lightning, and then, a mass of black stuff flew behind it, which looked like a foggy condensate. The research and analysis show that black lightning is produced by molecular aerogel aggregates, and these aggregates are hot and charged substances, which are very easy to explode or transform into spherical lightning, which is extremely dangerous.

According to observation and research, black lightning is generally not easy to appear in the near ground. If it appears, it is easy to bump into trees, masts, houses and other metals. It is generally tumor-like or mud-like. At first glance, it looks like a dirty thing, which is easily overlooked by people. However, it contains a lot of energy, so it is a kind of lightning clan with great danger and harm. In particular, black lightning is small in size and difficult to capture by radar; Moreover, it is very "favored" for metal objects; Therefore, it is called "aerial dark mine" by pilots. If the plane touches black lightning during the flight, the consequences will be unimaginable. Whenever black lightning is close to the ground, it is easy to be mistaken for a bird or something else, which is not easy to arouse people's vigilance and attention; If you hit it with a stick, it will explode quickly, which is in danger of breaking people to pieces. In addition, black lightning is similar to spherical lightning, and general lightning protection facilities, such as lightning rod, lightning ball and lightning protection network, can not protect black lightning; Therefore, it often reaches the vicinity of oil storage tanks, gas storage tanks, transformers and explosives depots with extremely strict lightning protection measures very smoothly. At this moment, don't go near it. We should avoid it and take personal safety as the priority.

Reasons for the formation of lightning

Air flow in thunderstorm clouds will generate static electricity due to the friction and decomposition of water molecules. There are two kinds of electricity. One is positive electricity with positively charged particles, and the other is 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 attract positive charges on the ground at the lower end of the cloud. The air between the cloud and the ground is an insulator. It will prevent the current of bipolar charges from passing through. When the charges in the thunderstorm cloud and the charges on the ground become strong enough, the two parts of charges will break through the air barrier and contact to form a strong current, and the positive charges and the negative charges will contact. When these opposite charges meet, neutralization (discharge) will occur. Intense charge neutralization will release a lot of light and heat. These emitted lights form [lightning ].

Most lightning is connected twice. The first time is called lead flash, which is an invisible air called lead, and it goes down to the place close to the ground. This charged air is like a wire, which establishes a guide for the second current. At the moment when the lead approaches the ground, a tie-back current jumps up along this guide. The flash produced by this reconnection is the lightning we can usually see.

The reason for thunder

Now we know that when the charge is neutralized, a lot of light and heat will be released, and a lot of heat will be released in an instant, which will heat the surrounding air to a high temperature of 3, degrees Celsius. When a strong current passes through the air, the air along the way will suddenly expand, and at the same time, it will push the surrounding air and make the air vibrate violently. At this time, the sound produced is [thunder]. (Don't forget to tell the baby that thunder happens at the same time, because the speed of light is much faster than the speed of sound, so we always see lightning before we hear it.)

If lightning falls near, we hear a deafening thunder. If lightning falls far away, we hear a rumbling thunder. This is because the sound waves are refracted by the atmosphere and reflected by ground objects.

2. The cloud must be large;

generally, lightning is not easy to occur in dry areas.

The process of lightning

If we put a high voltage between two electrodes and bring them closer. When two electrodes are close to a certain distance, an electric spark will appear between them, which is called "arc discharge".

Lightning generated by thunderstorm clouds is very similar to the arc discharge mentioned above, except that lightning is fleeting, but sparks between electrodes can exist for a long time. Because the high voltage between the two electrodes can be artificially maintained for a long time, it is difficult to replenish the charge in the thunderstorm cloud immediately after discharge. 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 average electric field intensity can reach several thousand volts/cm, and the local area can reach as high as 1 thousand volts/cm. Such a strong electric field is enough to break through the atmosphere inside and outside the cloud, so dazzling flashes are excited between the cloud and the ground or between different parts of the cloud and between different clouds. This is what people often say about lightning.

The process of a lightning bolt seen by naked eyes is very complicated. When the thunderstorm cloud moves somewhere, the middle and lower part of the cloud is a strong negative charge center, and the underlying surface opposite the cloud bottom becomes a positive charge center, forming a strong electric field between the cloud bottom and the ground. In the case of more and more charges and stronger electric field, a section of air column with strong ionization of the atmosphere first appears at the bottom of the cloud, which is called cascade leader. This ionized gas column extends to the ground step by step. The pilot of each step is a dim light beam with a diameter of about 5 meters, a length of 5 meters and a current of about 1 amps. It extends to the ground step by step at an average high speed of about 15, meters/second. When it is about 5-5 meters away from the ground, the ground suddenly strikes back. The channel for striking back is an ionization channel opened from the ground to the bottom of the cloud along the above-mentioned step pilot. The return stroke galloped from the ground to the bottom of the cloud at a higher speed of 5, km/s, emitting an extremely bright light beam, which lasted for 4 microseconds, and the current passed through exceeded 1, amps, which was the first lightning stroke. A few seconds later, a dim light beam from the cloud, carrying huge current, flew to the ground along the path of the first lightning strike, which was called the straight-channeling pilot. When it was about 5-5 meters away from the ground, the ground hit back again and formed a bright light beam, which was the second lightning strike. Then, like the second time, the third and fourth lightning strikes were produced. Usually, 3-4 lightning strokes constitute a lightning process. A lightning process lasts about .25 seconds. In this short time, a huge amount of electric energy will be released on the narrow lightning channel, thus forming a strong explosion, generating shock waves, and then forming sound waves to spread around. This is thunder or "thunder".

The structure of lightning

It is the linear lightning that has been studied in detail, so we will take it as an example to tell the structure of lightning. Lightning is a pulsed discharge phenomenon in the atmosphere. A lightning bolt consists of multiple discharge pulses, and the interval between these pulses is very short, only a few hundredths of a second. One pulse after another, the following pulse travels along the path of the first pulse. Now it has been clearly studied that each discharge pulse consists of a "pilot" and a "counterattack". Before the first discharge pulse bursts, there is a preparation stage-"step-leading" discharge process: under the impetus of strong electric field, the free charge in the cloud quickly moves to the ground. During the movement, electrons collide with air molecules, causing the air to ionize slightly and emit light. The leader of the first discharge pulse propagates downward step by step, like a glowing tongue. At first, the smooth tongue was only a dozen meters long. After a few thousandths of a second or even shorter, the smooth tongue disappeared. Then, on the same passage, a longer light tongue (about 3 meters long) appeared, and it disappeared in a blink of an eye; Then a longer smooth tongue appeared ... The smooth tongue approached the ground step by step in a "nibbling" way. After many times of discharge-disappearance, the smooth tongue finally reached the ground. Because the leader of this first discharge pulse propagates from the cloud to the ground step by step, it is called "step leader". On the passage of the light tongue, the air has been strongly ionized, and its conductivity has been greatly increased. The process of continuous ionization of air only takes place in a very narrow channel, so the current intensity is very high.

when the first pilot, the ladder pilot, reaches the ground, a large amount of charge flows from the ground to the cloud through the highly ionized air channel immediately. This current is so strong that the air passage is blazing, and a winding and slender light column appears. This stage is called "counterattack" stage, also called "main discharge" stage. The ladder pilot plus the first counterattack constitutes the whole process of the first pulse discharge, which lasts only one hundredth of a second.

74)this.width=74" border=undefined> After the first pulse discharge process, the second pulse discharge process occurred only after a very short time (4 seconds). The second pulse also starts from the pilot and ends at the return stroke. However, after the first pulse discharge, "the ice has been broken and the route has been opened", so the pilot of the second pulse will not go down step by step, but directly reach the ground from the cloud. This kind of pilot is called "direct channeling pilot". After the direct-channeling pilot reaches the ground, it takes about a few thousandths of a second to strike back and end the second pulse discharge process. Then the third and fourth ... Straight lead and return stroke, complete multiple pulse discharge process. Because each pulse discharge consumes a large amount of accumulated charge in the thunderstorm cloud, the main discharge process in the future becomes weaker and weaker, and the pulse discharge can not be stopped until the charge reserve in the thunderstorm cloud is exhausted, thus ending a lightning process.

the cause of lightning

the atmospheric electric field in thunderstorm is obviously different from that in sunny days. the reason for this difference is that there are charges accumulated in thunderstorm clouds and the polarity of thunderstorm clouds is formed, which produces lightning and causes great changes in atmospheric electric field. But how did the thunder cloud get its electricity? That is to say, what are the physical processes in the thunderstorm cloud that lead to its electrification? Why can so many charges accumulate in thunderstorm clouds and form a regular distribution? This section will answer these questions. As we have said before, the macroscopic process of thunderstorm cloud formation and the microphysical process in thunderstorm cloud are closely related to the electrification of the cloud. Scientists have made a lot of observations and experiments on the electrification mechanism of thunderstorm clouds and the regular distribution of charges, and accumulated a lot of information.