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Like an explosion, the rapidly expanding waves of compressed air create a loud, booming burst of noise. Because electricity follows the shortest route, most lightning bolts are close to vertical. The shock waves nearer to the ground reach your ear first, followed by the crashing of the shock waves from higher up. Vertical lightning is often heard in one long rumble.
However, if a lightning bolt is forked, the sounds change. The shock waves from the different forks of lightning bounce off each other, the low hanging clouds, and nearby hills to create a series of lower, continuous grumbles of thunder. They are also brighter than sprites and, as implied by their name, are blue in color. They were first recorded on October 21 , , on a video taken from the space shuttle as it passed over Australia.
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Again, this could be currents being generated from potential differences in the upper atmosphere caused by the same derivation of charge from the Solar Wind. Elves often appear as a dim, flattened, expanding glow around km miles in diameter that lasts for, typically, just one millisecond.
Their color was a puzzle for some time, but is now believed to be a red hue. Elves were first recorded on another shuttle mission, this time recorded off French Guiana on October 7 , This refers to the process by which the light is generated: the excitation of nitrogen molecules due to electron collisions the electrons possibly having been energized by the electromagnetic pulse caused by a discharge from the ionosphere.
On September 14 , , scientists at the Arecibo Observatory photographed a huge jet double the height of those previously observed, reaching around 80 km 50 miles into the atmosphere.
The jet was located above a thunderstorm over the ocean and lasted under a second. On July 22 , , five gigantic jets between 60 and 70 km 35 to 45 miles in length were observed over the South China Sea from Taiwan , as reported in Nature. Researchers have speculated that such forms of upper atmospheric lightning may play a role in the formation of the ozone layer. Alternatively, they may be due to differences in potential that result in current from the ozone layer. Most lightning is streak lightning. This is nothing more than the return stroke, the visible part of the lightning stroke.
Because most of these strokes occur inside a cloud, we do not see many of the individual return strokes in a thunderstorm. Lightning has been triggered directly by human activity in several instances. Lightning struck the Apollo 12 soon after takeoff and has struck soon after thermonuclear explosions. It has also been triggered by launching rockets carrying spools of wire into thunderstorms.
The wire unwinds as the rocket climbs, making a convenient path for the lightning to use.
These bolts are typically very straight, due to the path created by the wire. Extremely large volcanic eruptions, which eject gases and solid material high into the atmosphere can trigger lightning, and this phenomenon was documented by Pliny the Elder during the AD79 eruption of Vesuvius in which he perished. This is a form of cloud discharge, generally horizontal and at cloud base, with a luminous channel appearing to advance through the air with visually resolvable speed, often intermittently. The movement resembles the movement of a rocket , hence its name.
It is also one of the rarest of cloud discharges.
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Lightning requires the electrical breakdown of gas, so it cannot exist in a visual form in the vacuum of space. However, lightning has been observed within the atmospheres of other planets , such as Venus and Jupiter. Lightning on Jupiter is estimated to be times as powerful as, but fifteen times less frequent than, that which occurs on Earth.
Lightning on Venus is still a controversial subject after decades of study. During the Soviet Venera and U. Pioneer missions of the s and 80s, signals suggesting lightning may be present in the upper atmosphere were detected.
Thunderstormsare the primary source of lightning. Because people have been struck many miles away from a storm, seeking immediate and effective shelter when thunderstorms approach is an important part of lightning safety. Contrary to popular notion, there is no 'safe' location outdoors. People have been struck in sheds and makeshift shelters. A better alternative is to seek shelter within an enclosure of conductive material such as an automobile which is an example of a crude type of Faraday Cage.
Once inside the enclosure, it is advisable to keep away from any attached metallic components such as keys in an ignition, etc If thunder can be heard, there is a risk of being struck.
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Several different types of devices, including lightning rods and electrical charge dissipators , are used to prevent lightning damage and safely redirect lightning strikes. Lightning injuries result from three factors: electrical damage, intense heat, and the mechanical energy which these generate. While sudden death is common because of the huge voltage of a lightning strike, survivors often fare better than victims of other electrical injuries caused by a more prolonged application of lesser voltage.
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In a direct hit the electrical charge strikes the victim first. Counterintuitively, if the victim's skin resistance is high enough, much of the current will flash around the skin or clothing to the ground, resulting in a surprisingly benign outcome. Splash hits occur when lightning prefers a victim with lower resistance over a nearby object that has more resistance and strikes the victim on its way to ground.
Ground strikes, in which the bolt lands near the victim and is conducted through the victim and his or her connection to the ground such as through the feet, due to the voltage gradient in the earth, as discussed above , can cause great damage. A Thor Guard lightning prediction system. The most critical injuries are to the circulatory system , the lungs , and the central nervous system. Many victims suffer immediate cardiac arrest and will not survive without prompt emergency care, which is safe to administer because the victim will not retain any electrical charge after the lightning has struck of course, the helper could be struck by a separate bolt of lightning in the vicinity.
Others incur myocardial infarction and various cardiac arrhythmias , either of which can be rapidly fatal as well. The intense heat generated by a lightning strike can burn tissue and cause lung damage, and the chest can be damaged by the mechanical force of rapidly expanding heated air. Either the electrical or the mechanical force can result in loss of consciousness, which is very common immediately after a strike. Amnesia and confusion of varying duration often result as well. A complete physical examination by paramedics or physicians may reveal ruptured eardrums , and ocular cataracts may develop, sometimes more than a year after an otherwise uneventful recovery.
The lightning often leaves skin burns in characteristic Lichtenberg figures , sometimes called lightning flowers ; they may persist for hours or days and are a useful indicator for medical examiners when trying to determine the cause of death.
They are thought to be caused by the rupture of small capillaries under the skin, either from the current or from the shock wave. It is also speculated that the EMP created by a nearby lightning strike can cause cardiac arrest. There is sometimes spectacular and unconventional lightning damage.
Hot lightning high-current lightning which lasts for more than a second can deposit immense energy, melting or carbonizing large objects. One such example is the destruction of the basement insulator of the metre-high central mast of longwave transmitter Orlunda , which led to its collapse. Lightning prediction systems have been developed and may be deployed in locations where lightning strikes present special risks, such as public parks. Such systems are designed to detect the conditions which are believed to favor lightning strikes and provide a warning to those in the vicinity to allow them to take appropriate cover.
Old lightning scar Georgetown, South Carolina. A bolt of lightning can reach temperatures approaching 28, degrees Celsius 50, degrees Fahrenheit in a split second. This is about five times hotter than the surface of the sun. The heat of lightning that strikes loose soil or sandy regions of the ground may fuse the soil or sand into glass channels called fulgurites. These are sometimes found under the sandy surfaces of beaches and golf courses , or in desert regions. Fulgurites are evidence that lightning spreads out into branching channels when it strikes the ground. Trees are frequent conductors of lightning to the ground .
Since sap is a poor conductor, its electrical resistance causes it to be heated explosively into steam , which blows off the bark outside the lightning's path. In following seasons trees overgrow the damaged area and may cover it completely, leaving only a vertical scar.