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How Lightnings Form
March 3, 2009 15:03

A lightning

Russian physicists found that lightnings – giant electric discharges in atmosphere – appear due to flows of charged particles (so-called “cosmic rays”) from space, and are accompanied with gamma ray bursts.

The nature of lightning was discerned in 1749 by the famous American naturalist Benjamin Franklin, who revealed that they were electric discharges, appearing between a thunder storm cloud and the ground. So far scientists thought that a cloud accumulated negative charge, and an electric field formed between the cloud and Earth’s surface. When the field reached some certain threshold energy, a “breakdown” happened, and electric discharge – a lightning – formed. However, Russian physicists found that expected value of mentioned threshold energy was ten times higher than observed value of electric field that formed lightnings. Scientists suggested that lightning formation required some kind of “seed” – some priming particles with energies high enough. Natural priming particles are cosmic rays.

Russian researchers found out that lightnings caused a phenomenon, called “breakdown of escaping electrons” – an avalanche-type multiplication of fast electrons with energies of 0.1-10 megaelectron-volts in matter. The reason why such phenomenon took place was impact of space radiation. Flows of high-energy particles penetrate the atmosphere and bring “priming electrons”, which lead to a breakdown at energies that are ten times less than estimated values. Well, scientists do not mean that lightnings are “breakdowns of escaping electrons”, but these phenomena are closely related, because common electric discharges cannot display such high energies in gamma quanta. Experimental verification of the theory is very complicated, since “breakdown” caused a 50-meter-long “avalanche” under normal atmospheric conditions. In this case scientists need building giant machines for applying very powerful fields for simulating thunderstorm conditions.



Another effect, closely linked with lightnings is gamma ray bursts. Lightnings use to move by fits and starts – by so-called “steps”. Scientists discovered that during every “step” a lightning emits gamma quanta with energies, reaching tens of megaelectron-volts. Researchers have a special mountain site, where they conduct experiments on lightning behaviour in natural environment. Special counters measure gamma radiation in very short time periods and show absence of signals when there is no thunderstorm, and powerful gamma ray bursts during thunderstorm. These bursts correlate with radio-pulses, caused by storm processes.

Scientists emphasize that studying mechanisms of lightning formation helps understanding recently discovered phenomena, for instance, very powerful upper atmosphere discharges between thunderclouds and ionosphere (so-called “sprites”). This research provides new possibilities either in analysis of climatic change, or in mechanisms of affecting the atmosphere.

Source: Science News

Kizilova Anna

Tags: Russian Scientists     

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