Lightning is a massive natural electrostatic discharge produced during a thunderstorm. Lightning's abrupt electric discharge is accompanied by the emission of light. The electricity passing through the atmosphere rapidly heats and expands the air, producing lightning's characteristic thunder sound.
Lightning can also occur as a result of volcanic eruptions or violent forest fires which generate sufficient dust to create a static charge.
The second process is the build up of positive charges on the ground beneath the clouds. The earth is normally negatively charged with respect to the atmosphere. But as the thunderstorm passes over the ground, the negative charges at the bottom of the cumulonimbus cloud cause the positive charges on the ground to gather along the surface for several miles around the storm and becomes concentrated in vertical objects including trees and tall buildings. If you feel your hair stand up on end in a lightning storm beware. The negative charges from the cloud are pulling the positive charges inside your body to the top of your head and you could be in danger of being struck.
The third process is the generation of the lightning. When sufficient negatives and positives gather in this way, an electrical discharge occurs within the clouds or between the clouds and the ground, producing the bolt.
Research published in 2002[1] indicates that every lighting bolt also causes a similar but weaker electrodynamic pulse in the mesosphere, located 50 to 80 km (31 to 53 miles) above the earth, and above into the thermosphere.
This type of lightning is known as negative lightning due to the discharge of negative charge from the cloud, and accounts for over 95% of all lightning.
Statistics: an average bolt of negative lightning carries a current of 30 kiloamperes, transfers a charge of 5 coulombs, has a potential difference of about 100 megavolts, and lasts a few milliseconds.
As a result of their power, positive lightning strikes are considerably more dangerous. At the present time aircraft are not designed to withstand such strikes, since their existence was unknown at the time standards were set, and the dangers unappreciated until the destruction of a glider in 1999[1]. It has since been suggested that it may have been positive lightning that caused the crash of Pan Am flight 214 in 1963. Positive lighting is now also thought to be responsible for many forest fires.
Positive lightning has also been shown to trigger the occurrence of upper atmospheric lightning. It tends to occur more frequently in winter storms and at the end of a thunderstorm.
Statistics (based on a small number of measurements): an average bolt of positive lightning carries a current of 300,000 amperes, transfers a charge of up to 300 coulombs, has a potential difference up to 1 gigavolt (a thousand million volts), and lasts for tens or hundreds of milliseconds.
Heat lightning is nothing more than the faint flashes of lightning on the horizon from distant thunderstorms. Heat lightning was named because it often occurs on hot summer nights. Heat lightning can be an early warning sign that thunderstorms are approaching. In Florida, heat lightning is often seen out over the water at night, the remnants of storms that formed during the day along a seabreezefront coming in from the opposite coast.
Ball lightning is described as a floating, illuminated ball that occurs during thunderstorms. They can be fast moving, slow moving or nearly stationary. Some make hissing or crackling noises or no noise at all. Some have been known to pass through windows and even dissipate with a bang. Ball lightning has been described by eyewitnesses but rarely, if ever, recorded by meteorologists.
The engineer Nikola Tesla wrote in Electrical World and Engineer, March 5, 1904 "I have succeeded in determining the mode of their formation and producing them artificially." Later experimenters have been unable to reproduce his results.
Sprites are now well documented electrical discharges that occur high above the cumulonimbus cloud of an active thunderstorm. They appear as luminous reddish-orange neon-like flashes, last longer than normal lower stratospheric discharges (typically around 17 milliseconds), and are usually spawned by discharges of positive lightning between the cloud and the ground. Sprites usually occur in clusters of two or more simultaneous vertical discharges, typically extending from 65 to 75 km (40 to 47 miles) above the earth, with or without less intense filaments reaching above and below. Sprites are preceded by a sprite halo that forms due to heating and ionization less than 1 milisecond before the sprite. Sprites were first photographed on July 6, 1989, by scientists from the University of Minnesota and named after the mischievous sprites in the plays of Shakespeare. They are caused by the electric field of a lighting stroke (as opposed to the electromagnetic pulse that causes a sprite - see below).
Recent research [1] carried out at the University of Houston in 2002 indicates that some normal (negative) lighting discharges produce a sprite halo, the precursor of a sprite, and that every lightning bolt between cloud and ground attempts to produce a spite or a sprite halo.
Blue jets differ from sprites in that they project from the top of the cumulonimbus above a thunderstorm, typically in a narrow cone, to the lowest levels of the ionosphere 40 to 50 km (25 to 30 miles) above the earth. They are also brighter than sprites and, as implied by their name, are blue in colour. They were first recorded on October 21, 1989 on a video taken from the space shuttle as it passed over Australia.
Elves appear as a dim, flattened expanding glow around 400 km (250 miles) in diameter that lasts for, typically, just one millisecond. They occur in the ionosphere 100 km (60 miles) above the ground over thunderstorms. 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, 1990. Elves is a frivolous acronym for Emissions of Light and Very Low Frequency Perturbations From Electromagnetic Pulse Sources. This refers to the process by which the light is generated; the excitation of nitrogen molecules due to electron collisions (the electrons having been energised by the electromagnetic pulse caused by a positive lightning bolt.
On September 14, 2001, 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. Lightning was initially observed travelling up at around 50,000 m per second in a similar way to a typical blue jet, but then divided in two and speeded to 250,000 m / second to the ionosphere, where they spread out in a bright burst of light.
On July 22, 2002 five gigantic jets between 60 and 70 km (35 to 45 miles) in length were observed over the South China Sea from Taiwan, reported in Nature[1]. The jets lasted under a second, with shapes likened by the researchers to giant trees and carrots.
Researchers have speculated that such forms of upper atmospheric lightning may play a role in the formation of the ozone layer.
A bolt of lightning can reach temperatures approaching 50,000 degrees Fahrenheit (or about 28000 kelvin) in a split second. This is many times hotter than the surface of the sun. A result of this is that lightning strikes that hit a loose soil or sandy region of the ground may fuse the soil or sand into channels called fulgurites. These fulgurites are sometimes found under the sandy surfaces of beaches and golf courses or in desert regions. It is one evidence that lightning spreads out into branching channels when it strikes the ground.
Lightning is responsible for approximately 100 deaths a year in the United States alone. Lightning ranks second only to floods for storm related casualties in the U.S. every year. Many of these deaths could be prevented if basic precautions were taken when thunderstorms are expected in an area. Listening to a radio to keep up to date on storms in the area is the best way to prepare for safety.
One way to prepare for lightning safety is to install a device known as lightning conductor (commonly known as a lightning rod) for preventing damage by lightning to a building. A lightning conductor is a metal spike that is connected to earth by a low-resistance path. Should lightning strike a building, the current will travel through the conductor rather than through the fabric of the building, causing less damage.
Electrical equipment can be protected from lightning by a lightning arrester. This is a device that contains one or more gas-filled spark gaps between the equipment's cables and earth. Should lightning strike one of the cables, the high voltage will cause the gas in the spark gap to break down and become a conductor, providing a path for the lightning to reach the ground without passing through the equipment.
In movies and comics of the contemporary U.S. and many other countries, the lightning is often employed as an omnious, dramatic sign. It may herald a waking of a great evil or emergence of a crisis. Various novels and role playing games with fantasy tint involves wizardry of lightning bolt, weapon embodying the power of lightning, etc. The comic book character Billy Batson changed into the superheroCaptain Marvel by saying the word, "Shazam!" which called down a bolt of magic lightning to strike to change.
