Let lightning generate electricity? Lightning only provides enough electricity for the world for 9 days a year...

Nowadays, our lives are inseparable from electricity. You may know that most of the electricity we use in daily life comes from power plants, but do you know that the blue sky above our heads also stores a huge amount of electricity. When lightning and thunder roar, we can always feel the shock brought by this energy.

Since ancient times, people have been full of awe for thunder and lightning. In myths all over the world, there are gods who control thunder and lightning. For example, in ancient Chinese mythology, Lei Gong and Dian Mu control the power of thunder and lightning between heaven and earth to punish evildoers.

Is lightning in the sky the same as household electricity?

In 1752, Franklin conducted a famous kite experiment and cracked the secret of lightning. Franklin made a special kite with a piece of metal wire fixed on it and a long rope connected to the metal wire as the kite line. A key was also hung at the bottom of the rope. On a thunderstorm day, Franklin and his son flew the kite into the air.

At this moment, a flash of lightning flashed across the sky, and the fibers on the kite string stood up in an instant. Franklin was very happy. He carefully touched the key with his hand, and crackling sparks immediately jumped between his fingers and the key.

Afterwards, he introduced the electricity from the kite string into a Leyden jar, hurried home to conduct various electrical studies, and finally revealed that the lightning in the sky and household electricity are actually the same, and lightning is nothing more than a particularly intense electric spark discharge.

Franklin conducting his famous kite experiment

Later, scientists discovered that the earth itself carries a large amount of negative charge, and an equal amount of positive charge is distributed in the ionosphere from the ground to an altitude of about 50km, thus forming a vertically downward atmospheric electric field.

In a clear and open field, the electric potential will increase by about 130 volts for every meter of vertical elevation from the ground, which means that the electric field strength of the atmosphere is about 130V/m. In this way, an adult standing outdoors has a voltage of nearly 200 volts from the top of the head to the soles of the feet!

Why don’t you feel an electric shock when you walk on the road?

First of all, the reason why people get electric shock is that an electric current that exceeds the human perception passes through the human body. The human body is a conductor. If it accidentally touches 220-volt household electricity, it will be connected to the loop as a circuit element, causing an electric shock accident.

In the atmospheric electric field on a sunny day, the conductivity of the air is very poor, and the human body is always in a state of electrostatic equilibrium. That is, the voltage from the top of the head to the soles of the feet is actually close to zero, and almost no current flows through the body, so you cannot feel the electric shock.

However, if you are unfortunately struck by lightning, the large amount of electric current that passes through the human body in an instant will cause great harm.

Scientists have also discovered that there is a ground-to-space current of about 1800A between the ground and the ionosphere, which continuously transports positive charges to the earth. Theoretically, the electrical energy of the ionosphere will be consumed in about 5 minutes, and the atmospheric electric field will disappear.

But in fact, the value of the atmospheric electric field on a sunny day is quite stable, which means that there is a specific "power source" charging the ionosphere . What exactly is this specific "power source"? Lightning is actually the power source that charges the ionosphere. On average, about 100 lightning strikes occur per second around the world, and the lightning current brings negative charges from top to bottom to the earth, thus achieving a dynamic balance of charge and discharge between the earth and the ionosphere.

Traditional global atmospheric circuit model

Can we harness lightning?

Since lightning and everyday electricity are the same thing, there are more than a hundred lightning strikes around the world every second. How great it would be if so much lightning could be collected and converted into electricity for human use!

Classification of lightning

According to the location where lightning occurs, it is usually divided into two categories: cloud -to-ground lightning and ground-to-ground lightning. Lightning that hits the ground is called ground-to-ground lightning, accounting for about 1/3 of all lightning , while lightning that occurs in the cloud, that is, lightning that does not hit the ground, is called cloud-to-ground lightning, accounting for about 2/3 of all lightning.

For ground-to- ground lightning, if classified according to the polarity of neutralized charge , the lightning that transfers negative charge in the cloud to the ground is called negative ground-to-ground lightning, and its current direction is upward, accounting for about 90% of all ground-to-ground lightning, while the lightning that transfers positive charge in the cloud to the ground is called positive ground-to-ground lightning, and its current direction is downward, accounting for only about 10% of all ground-to-ground lightning.

According to the origin of lightning , the lightning that starts from the ground and develops upward is called upward lightning, which is generally rare, and the lightning that develops downward from the cloud is called downward lightning . Therefore, there are four types of ground lightning: downward negative ground lightning, downward positive ground lightning, upward positive ground lightning, and upward negative ground lightning, and the most common is downward negative ground lightning.

Four types of ground lightning

How is lightning formed?

Lightning generally occurs in cumulonimbus clouds with vigorous convection . The collision of particles such as hail and ice crystals in the cumulonimbus clouds causes the positive and negative charges to be continuously separated in the clouds. When they accumulate to a certain level, they will break through the air, and the lightning process begins.

At this time, the same breakdown point will send out two "advance troops" to extend the channel in opposite directions at the same time. One "advance troops" carries positive charge towards the negatively charged area in the cloud, and the other "advance troops" carries negative charge towards the positively charged area in the cloud until the entire lightning channel is opened.

Each "advance team" is called a "pioneer", and the two "advance teams" carrying opposite charges and extending at the same time are called "bidirectional leaders".

Take the downward negative ground lightning as an example. A small group of negative charges, as the "advance troops", moves from the cloud to the ground along the path of least resistance under the guidance of the electric field, shouldering the mission of opening up the cloud-to-ground lightning channel. On the path it passes, the air is ionized, forming an ionization channel, and the conductivity is greatly enhanced.

However, this "advance force" will also get tired. After walking a distance of about tens of meters in 1 microsecond, it will stop for about 50 microseconds to replenish energy, and then continue to move forward to explore the way. This process is like going down stairs, so the "advance force" is called a step-by-step guide. Sometimes the "advance force" will also split into multiple groups, which forms the branch shape of lightning.

When the "advance troops" reach a distance of tens to hundreds of meters above the ground, one or more "receiving troops" will set out from the ground to meet them, which is called the connecting leader. When the "advance troops" and the "receiving troops" successfully meet, the lightning channel between the cloud and the ground is completely opened, and the ground violently releases a large amount of positive charge to the newly opened channel. This process is called counterattack.

The peak current intensity of the return stroke is as high as tens of thousands of amperes. The rapid release of the return stroke energy will heat the original guide channel, and the temperature will reach 30,000K in an instant. The resulting high temperature and high pressure will cause the channel to expand rapidly and generate a shock wave, thus forming thunder.

The process of a leader and a return stroke constitutes an impulse discharge of lightning . Generally, lightning is composed of multiple impulse discharges. After the first impulse discharge, after a short rest, the second discharge process will occur. The second discharge process also starts from the leader and ends with the return stroke.

Since the lightning channel has been established after the first discharge process, the second leader no longer explores the path downward step by step, but directly reaches the ground from the cloud. This kind of leader is called an arrow leader or a straight leader . The return stroke guided by the straight leader is called a subsequent return stroke .

Schematic diagram of negative ground-to-ground lightning development

The power of lightning comes from its huge current, with a peak current intensity of tens of thousands of amperes, but its duration is extremely short, only tens of microseconds.

It is estimated that about 200-300 kWh of electricity can be obtained from a lightning bolt, which can be used by an average family for one month. There are 1.4 billion lightning strikes around the world every year, and cloud lightning cannot be collected . Theoretically, the total electricity provided by the 400 million ground lightning strikes that can be collected is about 100 billion kWh. According to statistics, the total global power generation in 2023 is 30 trillion kWh, and the electricity provided by lightning can only be used by the world for 9 days . From this perspective, the electricity from lightning is just a drop in the bucket.

In addition, we cannot accurately predict the location of lightning strikes, so it is difficult to capture natural lightning. It is also an extremely difficult task to reduce the high voltage of millions of volts of lightning to 220 volts and connect it to the power grid. It is also impossible to achieve it with current technology. Therefore, it is just a fantasy to capture lightning to provide electricity to serve mankind.

Benefits of Lightning

Although we cannot capture lightning at present, it plays a very important role in nature. When lightning occurs, nitrogen and oxygen in the air are completely ionized and combined to form nitrogen oxides, which are dissolved in rainwater and fall to the ground, becoming natural nitrogen fertilizer. The high concentration of negative oxygen ions produced by lightning can disinfect and purify the air, making people feel relaxed and happy. In addition, lightning can also promote biological growth.

To date, there are still many unsolved mysteries about lightning waiting for us to explore, and scientists have never stopped their research on lightning.

Author: Zhang Junchao, Aerospace New Meteorological Technology Co., Ltd.

Dai Yunwei, Meteorological Film and Television Center, China Meteorological Administration

Editor: Dong Xiaoxian