Lightning from the point of view of electricity

The electric nature of the lightning was opened in researches of the American physicist B. Franklin at the initiative of whom experiment on extraction of electricity from the storm cloud was made. Franklin experiment on clarification of the electric nature of the lightning is widely known. In 1750 it published work in which the experiment with use of the kite started during the thunderstorm was described. Franklin experience was described in Joseph Priestley's work.

Схема возникновения грозы

Scheme of emergence of the thunderstorm.

Average length of the lightning of 2,5 km, some discharges stretch in the atmosphere for distance to 20 km.

How there is lightning forming? Most often the lightning arises in cumulus cumulonimbus clouds, then they are called storm. Sometimes the lightning is formed in layered cumulonimbus clouds and also at volcanic eruptions, the tornado and dust storms.

Схема возникновения молнии

Scheme of emergence of the lightning: and — forming; — discharge.

It is necessary for emergence of the lightning that in rather small (but it is not less of some critical) the volume of the cloud electric field with the strength sufficient to start electric discharge was formed (~ 1 MV/m), and in large part clouds there would be the field with the average strength sufficient for maintenance of the begun discharge (~ 0,1-0,2 MV/m). Electrical energy of the cloud turns into lightnings in thermal and light.

Linear lightnings which belong to so-called electrodeless discharges as they begin (and come to an end) in accumulations of the charged particles are usually observed. It defines their some still not explained properties distinguishing lightnings from discharges between electrodes.

So, lightnings are not be shorter than several hundred meters; they arise in electric fields much weaker, than fields at interelectrode discharges; collecting the charges transferred by the lightning happens for thousand fractions of a second from billions of small, well isolated from each other particles located of several sq.km.

Development of the lightning in storm clouds is most studied, at the same time lightnings can pass in clouds (intra cloudy lightnings), and can strike to the earth (land lightnings).

Land lightnings

Схема развития наземной молнии

Scheme of development of the land lightning: and — two steps of the leader; 1 — the cloud; 2 — streamers; 3 — the channel of the step leader; 4 — the crown of the channel; 5 — the pulse crown on the head of the channel; in — formation of the main channel of the lightning (To).

Development of the land lightning consists of several stages. At the first stage, in the zone where electric field reaches critical value, the ionization by collision created in the beginning by the free electrons which always are available in the small amount in air which under the influence of electric field get considerable speeds towards the earth begins and, facing the molecules making air ionize them.

On more modern representations, the discharge is initiated by high-energy cosmic rays which start the process which received the name of breakdown on the running-away electrons. Thus, there are electron avalanches passing into threads of electric discharges — the streamers representing well carrying out channels which, merging, give rise to the bright thermoionized channel with high conductivity — to the step leader of the lightning.

The movement of the leader to the land surface happens steps in several tens of meters to speed ~ 50 000 kilometers per second then its movement stops on several tens of microseconds, and the luminescence strongly weakens; then in the subsequent stage the leader moves ahead on several tens of meters again.

The bright luminescence covers at the same time all passable steps, then the stop and weakening of the luminescence follow again. These processes repeat at the movement of the leader to the Earth's surface with the average speed of 200 000 meters per second. In process of advance of the leader to the earth field gradient on its end amplifies, and under its action the response streamer connecting to the leader is thrown out of speakers on the Earth's surface of objects. This feature of the lightning is used for creation of the lightning arrester.

In the final stage on ionized the leader the channel is followed by the return (from below up), or main, the lightning discharge which is characterized by currents from tens to hundreds of thousands of amperes, brightness considerably exceeding the leader's brightness and the high speed of advance in the beginning reaching to ~ 100 000 kilometers per second, and at the end of decreasing to ~ 10 000 kilometers per second.

Temperature of the channel at the main discharge can exceed 25 000 °C. Length of the channel of the lightning can be from 1 to 10 km, diameter — several centimeters. After passing of the impulse of current ionization of the channel and its luminescence weaken. In the final stage the lightning current can last the 100-th and even the tenth fractions of a second, reaching hundreds and thousands of amperes. Such lightnings are called long, they most often cause the fires.

The main discharge discharges quite often only the part of the cloud. The charges located at big heights can give rise to the new (arrow-shaped) leader moving continuously with the speed of thousands kilometers per second. Brightness of its luminescence is close to brightness of the step leader. When the arrow-shaped leader reaches the Earth's surface, the second main blow, similar follows the first.

Usually the lightning includes several repeated discharges, but their number can reach also several tens. Duration of the repeated lightning can exceed 1 sec. Shift of the channel of the repeated lightning wind creates the so-called tape lightning — the shining strip.

Intra cloudy lightnings

Схема процесса электризации грозового облака и развития грозового разряда на наземный объект

The scheme of process of electrization of the storm cloud and development of lightning discharge on the land object.

Intra cloudy lightnings include usually only warranty stages, their length fluctuates from 1 to 150 km. The share of intra cloudy lightnings grows in process of shift to the equator, changing from 0,5 in midlatitudes to 0,9 in the equatorial strip. Passing of the lightning is followed by changes of electric and magnetic fields and the radio emission, so-called atmospherics.

The probability of defeat grows at the lightning of the land object in process of increase in its height and with increase in conductivity of the soil at surfaces or at some depth (action of the lightning protector is based on these factors). If in the cloud there is electric field sufficient for maintenance of discharge, but insufficient for its emergence, the role of the initiator of the lightning can execute the long metal rope or the airplane, especially if it strongly electrically is loaded. Thus lightnings in layered and rain and powerful cumulus clouds "are sometimes provoked".

In every second about 50 lightnings hit to the Earth's surface, and on average each its square kilometer the lightning strikes six times in the year.

People and lightning

Схема защиты дерева от ударов молнии

Scheme of protection of the tree against lightning discharges.

Lightnings — serious threat for life of people. Defeat of the person or the animal the lightning often happens on open spaces since electric current goes on the shortest way "the storm cloud earth". Often the lightning gets to trees and transformer installations on the railroad, causing their ignition.

Defeat by the normal linear lightning in the building is impossible, however there is the opinion that so-called globular lightning can get through slots and open windows. Normal lightning discharge is dangerous to the television and radio antennas located on roofs of high-rise buildings and also to the network equipment.

In the organism of victims of the lightning the same pathological changes, as are noted at defeat by the current. The victim faints, falls, at it spasms can begin, breath and heartbeat often stops. On the body it is usually possible to find "current tags" - places of the entrance and the exit of electricity.

These are the treelike light pink or red strips disappearing when pressing by fingers (remain within 1-2 days after death). They — result of expansion of capillaries in the zone of contact of the lightning with the body. In case of death sudden respiratory standstill and heartbeat from direct action of the lightning on the respiratory and sosudodvigatelny centers of the medulla is the reason of the termination of the trial vital signs.

At defeat by the lightning first aid has to be urgent. In hard cases (respiratory standstill and heartbeat) resuscitation is necessary, has to render it, without expecting health workers, any witness of misfortune. Resuscitation is effective only the first minutes after defeat by the lightning, in 10-15 minutes it is, as a rule, already inefficient. The emergency hospitalization is necessary in all cases.

Victims of lightnings

Основные пути проникновения перенапряжений в здания и сооружения объектов охраны

Main ways of penetration of retension to buildings and constructions of objects of protection.

In mythology and literature:

Historic figures:

Interesting facts

Trees and lightning

High trees — the frequent target for lightnings. On relic trees long-livers it is easily possible to find multiple scars from lightnings. It is considered that odinochno the standing tree is surprised the lightning more often though in some forest areas scars from lightnings can be seen almost on each tree. Dry trees from the lightning discharge light up. More often lightning discharges happen are sent to the oak, is the most rare in the beech that, apparently, depends on different amount of greasy oils in them representing the big resistance to electricity.

The lightning passes in the tree trunk on the way of the smallest electrical resistance, with allocation of the large amount of heat, evaporating water which splits the tree trunk or more often tears off from it sites of bark, showing the way of the lightning.

During the next seasons trees usually recover the damaged fabrics and can close the wound entirely, having left only the vertical scar. If the damage is too serious, wind and wreckers finally kill the tree. Trees are natural lightning protectors and, as we know, provide protection against the lightning discharge for nearby buildings. The buildings planted near high trees catch lightnings, and high biomass of root system helps to ground lightning discharge.

Do musical instruments of the trees struck with the lightning, attributing them unique properties.

COMMENTS
  • To add the comment

0000000000000000
Top