Lightning has been studied for centuries, but there is still a lot of unclear in their nature. How a discharge in a cloud originates, what is ball lightning, why gamma quanta are emitted during a thunderstorm - these questions have yet to be answered. RIA Novosti talks about the most current research in the field of atmospheric electricity.
"Lightning is an electrical discharge that moves in the atmosphere along a thin hot plasma channel - the leader - from cloud to earth, between clouds or rises from tall buildings," says Alexander Kostinsky, PhD in Physics and Mathematics, Deputy Director of MIEM named after … A. N. Tikhonova, participant of the international project "Lightning and their manifestations", supported by the Ministry of Education and Science and the Russian Science Foundation.
A cloud is needed for lightning to occur. Rising upward, it expands, cools, small drops of water, snowflakes, hail and many other particles of different sizes, which are called hydrometeors, are formed in it. In fact, an aerosol is formed inside the cloud, its particles rub against each other and acquire charges of different signs.
After moisture condensation, the cloud heats up a little and rises higher, drawing in the surrounding air. This is why thunderstorms are accompanied by increased winds. Inside the cloud, layers of positively and negatively charged particles are added, rain falls, intra-cloud discharges begin, some of them reach the ground.
The sprite appears in the upper atmosphere after a strong lightning discharge into the ground.
The lightning channel conducts a strong electric current thanks to plasma - a highly ionized gas. The high-speed camera photos show the lightning leader branching out as it moves. As he gets closer to the ground, from high points - skyscrapers, TV towers - rising leaders rush towards him. A powerful current flows through the connected channel at a speed only several times lower than the speed of light. It is this flash that we see when struck by lightning.
“We observe lightning when it is big, energetic, sets fires, kills animals, disables equipment. But the moment of its origin in the cloud has remained one of the main scientific mysteries for a hundred years now,”the scientist continues.
There are many hypotheses on this score, which are very complex and do not explain all the observed phenomena. Measured: To break through just one centimeter of air, a voltage of thirty thousand volts is required. This means that there must be very strong electric fields in the cloud, but measurements give several times lower values.
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“Every second about a hundred lightning strikes the ground, and no one knows how they originate. Moreover, physical measurements show that they should not form in the clouds,”notes Kostinsky.
Time-lapse photography of lightning strikes.
Ball lightning
A separate puzzle is ball lightning. Thousands of evidences about it from different historical epochs are known, scientists even experimentally obtained “spherical plasma formations” in the laboratory, but it is not possible to prove that this is the natural phenomenon under study. The main question (besides nucleation) is why a charged plasma clot exists in the atmosphere for so long - seconds and minutes. In theory, without external feed, it should cool down in thousandths of a second, losing conductivity.
Some researchers assumed that ball lightning was an optical effect, but several years ago, Chinese scientists filmed a ball glow during lightning strikes, which lasted for almost a second, on a high-speed camera with an optical spectrometer. This clarified little about the nature of the phenomenon, but confirmed its reality.
More mysteries
In 1989, thanks to satellites, a completely new type of atmospheric electricity was discovered - sprites. They arise at an altitude of 70-85 kilometers in the electric field, which is formed after a strong lightning strike into the ground, when the lower part of the cloud is discharged. From space, we saw blue jets and giant jets - electrical discharges of great length. They originate at the tops of thunderclouds and reach a height of 90 kilometers.
Jet - discharge going from the cloud to a height of 90 kilometers. Mauna Kea Observatory, Hawaii.
In 1991, American satellites recorded bursts of gamma rays, that is, hard X-rays, during thunderstorms. These data were immediately classified, deciding that ground nuclear tests were being carried out somewhere. Three years later, after making sure that the source of radiation were thunderstorms, the results of the observations were published.
“Such energy quanta rarely come to Earth, even from solar flares. It turns out that the cloud acts as an accelerator of elementary particles, namely electrons and, perhaps, positrons. This area is called atmospheric high-energy physics,”says Alexander Kostinsky.
In the 2000s, it turned out that inside the cloud at an altitude of about ten kilometers, sources of radio emission are formed that are much more powerful than those accompanying lightning. They last only a few microseconds. They were called compact intracloud discharges. There is no generally accepted theory of their appearance yet.
Interest in electrical discharges in the atmosphere of other planets of the solar system is still unabated. Images of thunderstorms on Jupiter and Saturn were obtained, observations in the radio range showed discharges on Uranus and Neptune. The question with Venus is still open. But there is no thunderstorm on Mars and Titan.
According to Kostinsky, the science of lightning is now experiencing a real boom. After all, thunderstorms and lightning are very dangerous, destructive natural phenomena. In addition, scientists are faced with practical tasks - to protect people and animals from atmospheric discharges, structures, windmills, aircraft.
Lightning discharges in the atmosphere on the night side of Jupiter. Galileo Orbiter, 1998.
Tatiana Pichugina
