I don’t believe in astrology; I’m a Sagittarius and we’re skeptical.
Arthur C. Clarke
Good day to all! Today I want to talk about a fairly common, but at the same time very spectacular and bewitching atmospheric phenomenon – about lightning.
Many people attributed lightning to a divine nature. A lot of supreme gods (or, at least, gods from the big leagues) use lightning almost as a mandatory attribute: both the Greco-Roman Zeus-Jupiter, the Slavic Perun, the Lithuanian Perkunas, the Scandinavian Thor, the Finnish Yukko, the Mesopathic Teshab, and even the Indian Indra always have lightning in their arsenal.
But if we return to a more prosaic, materialistic approach, and open a regular school textbook or popular science encyclopedia, we will find out that lightning is “a natural discharge of large accumulations of electric charge in the lower atmosphere. Lightning discharges can occur between neighboring electrified clouds or between an electrified cloud and the earth. The discharge is preceded by the occurrence of a significant difference in electric potentials between neighboring clouds or between the cloud and the earth due to separation and pollination of atmospheric electricity as a result of natural processes such as rain, snowfall, etc. The resulting potential difference can reach a billion volts, and the subsequent discharge of accumulated electric energy through the atmosphere can create short-term currents of tens or even hundreds of thousands of amperes…”
We also learn that back in 1752, an American statesman and scientist B. Franklin conducted an experiment with a kite, to which a metal key was attached, and received sparks from the key during a thunderstorm. Over the next 250 years, the phenomenon of lightning has been intensively studied, hundreds of books and articles have been written. It seems that everything is known, logical and without any magic… Or not everything? What other mysteries and miracles does the “heavenly fire” hide from us?
Dmitri Burshtyn: Since ancient times, lightning has been an object of lively interest. With the development of physics in the 17-18 centuries, great progress was made in understanding this phenomenon, and by the beginning of the 19th century, the electrical nature of lightning had no doubt. It only remained to understand the mechanism of electricity generation in thunderclouds and the parameters of a lightning discharge. But getting answers to these questions was not so simple. But first things first…
Types of Lightning
As already indicated by the administrator, ordinary lightning is formed in the lower atmosphere. Its length can vary from a few hundred meters to 300 kilometers, the current in a lightning discharge on Earth reaches 10-500 thousand amperes, and voltage – from tens of millions to a billion volts. [Hasbrouck, Richard. Mitigating Lightning Hazards Archived October 5, 2013, at the Wayback Machine, Science & Technology Review May 1996]
There are three types of ordinary lightning:
- Lightning Cloud-Ground (CG) – the usual lightning between a cloud and a ground. Most studied.
- Intracloud lightning (IC) – a lightning between positively and negatively charged areas inside the same thundercloud. By their characteristics, they are similar to cloud-to-ground lightning but are not visible from the ground. They can be observed in the form of an instant glow inside a cloud.
- Cloud-to-cloud or intercloud lightning (CC) – same as intracloud lightning, but between different clouds.
Moreover, in the early 90s of the last century, several more types of lightning were discovered using observations from space:
- Jets (at an altitude of 10-50 km) appear from the top of a thundercloud, but are not directly related to the lightning of the cloud-earth type. They spread in narrow cones, arising and disappearing at heights of 40-60 km. Can be observed by aircraft pilots.
- Sprites (at an altitude of 50-100 km) – may appear right above an active thunderstorm as a large but weak flash. They usually occur simultaneously with powerful positive cloud-to-ground lightning strikes (a rare occurrence, <10% of all cloud-to-ground lightning, which are usually negative). They can occur at an altitude of several tens of kilometers above a thundercloud. Sprites are mostly red and usually last no more than a few seconds, and their shape is described as resembling a jellyfish, carrots or columns. Since sprites are not very bright, they can only be seen at night. They are rarely seen with the human eye, which is why they are most often obtained using highly sensitive cameras.
- ELVES (acronym for Emissions of Light and Very Low Frequency Perturbations due to Electromagnetic Pulse Sources, observed at altitudes > 100 km) are rapidly expanding disk-shaped areas of luminescence that can reach 500 km across. They last less than one thousandth of a second and occur over areas where cloud-to-ground lightning appears. Scientists believe that elves arise when a powerful electromagnetic pulse propagates into the ionosphere. Elves were discovered in 1992 using a video camera in low light on a space shuttle.
Thundercloud Electrification
The details of the charging process are still being studied by scientists, but there is general agreement on some of the basic concepts of thunderstorm electrification.
Inside a thundercloud, strong updrafts raise droplets of supercooled water and tiny light ice crystals. At the same time, heavier particles of snow graupel (it’s like hail, but smaller) falls toward the lower part of the cloud under the influence of gravity. All these particles collide with each other, and as a result, the particles of graupel will receive a negative charge (which accumulates in the lower part of the cloud), and water droplets will receive, respectively, a positive charge that accumulates in the upper part of the cloud.
This explains the appearance of a huge electric charge in a thundercloud.
As a result, a negative charge accumulates in the lower part of the thundercloud, a positive charge in the upper part of the cloud, and a positive mirror charge forms on the ground under the cloud.
Lightning Discharge
So, we have suitable conditions for the formation of lightning – a negatively charged cloud and a positively charged earth (a positive charge is induced in the area under the cloud by the electrostatic field of negative charges in the cloud).
However, the air between the cloud and the earth is a good insulator (even wet air). But for an electric discharge to occur, an electrically conductive channel between the negative and positive charges must be formed. That is, even under suitable conditions, it is necessary to ionize a column of air from a few hundred meters to several hundred kilometers long. But the paradox is that the electric field required for ionizing such a long column of air should be at least ten times greater than electric field created by charges in the cloud and on the ground.
The answer to this puzzle was found only a few years ago. For the ionization of air in the process of lightning discharge are responsible… cosmic rays!
Cosmic rays are a stream of charged particles (mainly protons and (~10%) from alpha particles (helium nuclei)) moving at a speed very close to the speed of light, and having tremendous energy, millions of times bigger compare to energy achievable at the most powerful particle accelerators such as the Large Hadron Collider. The sources of these ultra-high energy particles are in deep space, outside of the solar system, and sometimes, even outside our galaxy. In accordance with modern models of a possible mechanisms for acceleration of particles to ultra-high velocities, cosmic ray sources are:
- The active galactic nuclei – giant black holes in the centers of galaxies.
- Supernova explosions – explosions of massive stars at the final stage of their evolution, accompanied by the release of a huge amount of energy.
- Quasars (quasi-stellar objects) – very bright objects, brighter than dozens of galaxies together, and usually located very far from us. According to modern concepts, quasars are the active galactic nuclei at an early stage of galaxy formation process.
When cosmic rays (with average density ~1 particle per second per square meter) strikes the Earth’s atmosphere, they collide with air molecules and produces showers of secondary particles (electrons, positrons, mesons and neutrinos) with huge velocities, and correspondingly huge energies. These secondary particles reach the lower atmosphere and even the surface of the earth, and if they pass through a thundercloud, they cause a “runaway breakdown”. In simple words, cosmic rays bring missing energy needed to ionize a very long column of air.
[A.V. Gurevich, “Runaway Breakdown and the Mysteries of Lightning”, Physics Today 2005, p.37]
Stages of Lightning Formation
Under the influence of the electric charge accumulated in a thundercloud and with the help of cosmic rays, a stepped leader of lightning is formed – a zigzag line of ionized air (electrically conductive plasma channel).
Usually, the lightning leader splits into many “branches” to form a “tree-like” structure (by the way, visually similar to a shower of secondary particles produced by cosmic rays). The typical length of such branches, called streamers, is 40-50 meters, and they spread at an average speed of about 200 kilometers per second from top to bottom.
When a leader approaches close to the ground, a positively charged upward streamer starts rising from ground (usually a high-standing object like a tree or a lightning rod of a building) towards a stepped leader (as the lighting leader approaches the ground, electrostatic field increases, ionizing air near the ground surface).
When the upward streamer meets one of the branches of the stepped leader, a conducting channel is formed between the negatively charged cloud and the positively charged earth. At this moment, in a very short time (a few milliseconds), a huge electric charge distributed across the cloud over an area of several square kilometers, gathers at the top point of the leader and flows down to the ground with a huge speed (up to 100,000 kilometers per second). The temperature of the lightning channel during the main discharge can reach up to 30,000° C.
The main discharge often discharges only part of the cloud. Charges located at high altitudes can give rise to a new (arrow-shaped) leader, moving continuously at a speed of thousands of kilometers per second. The brightness of its glow is close to the brightness of a stepped leader. When the arrow-shaped leader reaches the surface of the earth, a second major discharge follows, similar to the first one. Usually lightning includes several repeated discharges, but their number could be up to a few dozens.
Let’s Summarize
It is amazing that this formidable and mysterious atmospheric phenomenon on a small planet somewhere in the Milky Way is directly related to no less mysterious processes taking place in distant galaxies and deep space. The connection of natural phenomena on Earth with celestial bodies has long been known, for example, the gravity of the Moon, causing tides, or flashes on the Sun and the magnetic storms caused by them. But all this is nearby, some 300,000 km from Earth, well, the maximum is within the limits of the solar system. And cosmic rays causing lightning come to us from distant galaxies located at a distance of millions of light years from us!
That is, fantastic ideas about the Cosmos as a large single organism, so beloved by ancient and modern astrologers and causing smiles among some scientists, are not so unfounded. Moreover, for those who have suffered in one way or another from a lightning strike (and the number of such unfortunates is up to 24,000 (!!!) per year [Holle, RL (2016) The number of documented global lightning fatalities. Preprints, 24th Int. Lightning Detection Conf. And Sixth Int. Lightning Meteorology Conf., San Diego, CA, Vaisala, 1-4], the main postulate of astrology about the influence of distant stars on the fate of a particular person is scientifically correct literally!