Lightning can be one of the most picturesque visions in nature, and the one of the most deadly occurrences when it strikes. Lightening flashes occur on earth about 100 times every second, traveling at speeds up to 60,000 m/s, and can reach temperatures of 54,000°F (30,000 °C), hot enough to fuse silica sand into petrified lightning — known as glass channels or fulgurites — which are usually hollow and can extend some distance into the ground.
Typically occurring during thunderstorms, 80% of flashes are in-cloud and 20% are cloud-to-ground. Lightning can also occur within the ash clouds from volcanic eruptions, dust storms, or caused by violent forest fires which generate sufficient dust to create a static charge. There are more than 16 million lightning storms in the U.S. alone every year.
The odds of being struck by lightning are approximately 1 in 576,000 and the chance of actually being killed by lightning is about 1 in 2,320,000.
Scientists have yet to agree on how lightning initially forms, studying root causes ranging from atmospheric perturbations — wind, humidity, friction, and atmospheric pressure — to the impact of solar wind and accumulation of charged solar particles. Ice inside a cloud is considered to be a key factor in development, and may cause a forcible separation of positive and negative charges within the cloud, consequently assisting in the formation of lightning.
Lightening over Ayers Rock/ Uluru. Photo Taipan2007
The return stroke of a lightning bolt — the visible bolt itself — follows a charge channel only about a half-inch (1.3 centimeters) wide. Most lightning bolts are about 1 mile (1.6 kilometers) long, with the longest recorded length at 118 miles (190 kilometers) sighted near Dallas, Texas.
Lightening can carry an electric current of 40 kiloamperes (kA) up to 120 kA, and transfers a charge of 5 coulombs and 500 MJ. The voltage depends on the length of the bolt, with the dielectric breakdown of air being 3,000,000 volts per yard / meter which works out to about one gigavolt (one billion volts) for a 1,000 foot (300 meter) lightning bolt.
It can heat nearby air to about 18,000 °F (10,000 °C) almost instantly, which is nearly twice the temperature of the Sun’s surface. The heating creates a shock wave heard as thunder.
Voltage and currents for lightening strikes will vary by different locations. Florida has the largest number of recorded strikes over an entire summer season in the U.S. The area has very sandy ground in some areas and conductive saturated mucky soil in others, and is bordered by the ocean on 3 sides, resulting in daily development of sea and lake breeze boundaries that collide to produce thunderstorms.
Arizona has very dry, sandy soil and very dry air with cloud bases as high as 6,000 to 7,000 feet (1800 to 2100 meters) above ground level, with very long and thin purplish lightening discharges that crackle. Oklahoma has fairly soft, clay-rich soil, with cloud bases only reaching 1,500 to 2,000 feet (450 to 600 meters) above ground level, which produces blue-white explosive lightning strikes that are very hot (high current) and cause sudden, explosive noise when the discharge comes.
Photo Vermin Inc
Photo Steve took it
Scientists from NASA have found the radio waves created by lightning clear a safe zone in the radiation belt surrounding the earth which can potentially be a safe haven for satellites, offering them protection from the Sun’s radiation, which is implemented at an area called the Van Allen Belt slot.
High speed videos of lightening examined frame-by-frame reveal that most strikes are made up of 3 to 4 individual strokes or more, creating a noticeable “strobe light” effect.
Each re-strike is typically separated by 40 to 50 milliseconds of time, preceded by intermediate dart leader strokes again to the initial stepped leader. The stroke usually re-uses the discharge channel taken by the previous stroke. The sound of thunder from a lightning strike is prolonged by successive strokes.
Lightning can also strike indoor pools, directed into the pump by electrical circuits from outdoor power poles, which could potentially kill people who are swimming or walking on wet floors around a pool.
A single lightning strike can have a potential of a billion volts and deliver 100,000 amperes of current. If a bolt directly hits a marine animal swimming on the surface, it will undoubtedly hurt or kill the animal. Lightning strikes have killed or injured people on the surface more than 30 yards away from it.
Forms of Lightning
Various types of lightning have been given names for their particular characteristics. Most lightning is streak lightning which is basically the return stroke, the visible part of the lightning stroke. Since most of these strokes occur inside a cloud, we don’t see many of the individual return strokes in a thunderstorm.
Positive lightning makes up less than 5% of all lightning, occurring when the leader forms at the positively charged cloud tops, with the result of a negatively charged streamer issuing from the ground. The effect is a discharge of positive charges to the ground.
Research has shown that positive lightning bolts are typically 6 to 10 times more powerful than negative bolts, last around 10 times longer, and can strike tens of miles / kilometers from the clouds. During a positive lightning strike, huge quantities of ELF and VLF radio waves are generated.
An anvil to ground lightning bolt — a form of positive lightening which emanates from the anvil top of a cumulonimbus cloud where the ice crystals are positively charged — is a sign of an approaching storm, and if one occurs in a clear sky, it’s colloquially known as “bolts from the blue.” The leader stroke of lightning flows in a nearly horizontal direction until it veers toward the ground. They usually occur miles ahead of the main storm and will sometimes strike without warning on a sunny day.
As a result of their greater power, positive lightning strikes are considerably more dangerous. At the present time, aircraft are currently not designed to withstand these strikes since their existence was unknown at the time standards were set.
But aircraft operating in U.S. airspace have been required to have lightning discharge wicks to reduce the chances of being struck after one caused an in-flight explosion and subsequent crash of Pan Am Flight 214, a Boeing 707 in 1963.
Cloud to Ground
Cloud-to-ground lightning is a massive lightning discharge between a cumulonimbus cloud and the ground initiated by the downward-moving leader stroke. It’s the second most common form, posing the greatest threat to life and property of all known types of lightening.
Cloud to ground. Photo Kuby
Cloud to Cloud
Lightning discharges can occur between areas of cloud without contacting the ground, most common between the anvil and lower reaches of a thunderstorm. They can sometimes be seen at great distances at night as so-called “heat lightning,” which may only be a flash of light without thunder.
Another term used for cloud-to-cloud or cloud-to-cloud-to-ground lightning is “Anvil Crawler,” due to the habit of the charge usually originating from beneath or within the anvil and scrambling through the upper cloud layers of a thunderstorm, typically generating multiple branch strokes which are dramatic to watch, usually seen as a thunderstorm passes over you or begins to decay.
Ground to Cloud
Ground-to-cloud lightning is a lightning discharge between the ground and a cumulonimbus cloud from an upward-moving leader stroke.
Staccato lightning is a cloud to ground lightning strike which is a short duration stroke that appears as a single very bright flash and often has considerable branching.
Also referred to as ‘heat lightening,’ dry lightening occurs in thunderstorms which produce no precipitation at the surface, and the most common natural cause of wildfires.
One of the rarest of cloud discharges, rocket lightening is a form of cloud discharge, generally horizontal and at the cloud base, with a luminous channel appearing to advance through the air with visual speed, often intermittently. The movement has been compared to that of a skyrocket, hence the name.
Bead lightning is a fairly rare type of cloud-to-ground lightning which appears to break up into a string of short, bright sections which last longer than the usual discharge channel.
Some theories to explain it as witnesses seeing portions of the lightning channel end on that appear especially bright, others claim the width of the lightning channel varies — as the lightning channel cools and fades, the wider sections cool more slowly and remain visible longer, appearing as a string of beads.
Photo V. Mason
Photo Labels 30
Ribbon lightning occurs in thunderstorms with high cross winds and multiple return strokes. The wind will blow each successive return stroke slightly to one side of the previous return stroke, causing a ribbon effect.
Ball lightning is described as a floating, illuminated ball that occurs during thunderstorms that can be fast moving, slow moving or nearly stationary. They have been known to pass through windows and even dissipate with a bang, but some make hissing or crackling noises or no noise at all.
Ball lightning is generally 8 to12 inches (20 to 30 centimeters) in diameter, but there have been reports of several yards / meters in diameter. Ball lightning has been seen in tornadoes, and has been seen to split apart into 2 or more separate balls and recombine. Vertically-linked fireballs have also been reported.
There have been reports of ball lightning carving trenches in the peat swamps in Ireland. Due to its strange behavior ball lightning has been mistaken for UFO’s by numerous witnesses, with many false reports of alien spacecraft sightings.
Several theories have advanced for ball lightning with none being universally accepted, but some say it’s created when lightning strikes silicon in soil, and has been created in a lab in this manner.
The most famous story of ball lightning occurred when 18th-century physicist Georg Wilhelm Richmann installed a lightning rod in his home and was struck in the head and killed by a “pale blue ball of fire.”
Thunderstorm at Leinster Western Australia. Photo Jock49
Fort Gratiot, Michigan. Photo MD Provost
Sometimes called megalightning, reports by scientists of strange lightning phenomena above storms date back to at least 1886, but it’s only in recent years that fuller investigations have been made.
Sprites are electrical discharges that occur high above some types of thunderstorms, appearing as luminous reddish-orange or greenish-blue plasma-like flashes that last longer than normal lower stratospheric discharges, triggered by the discharges of positive lightning between the thundercloud and the ground.
Sprites often occur in clusters of 2 or more, generally spanning a distance from 50 to 90 miles (80 to145 kilometers) above ground, with what appear to be tendrils hanging below and branches reaching above. They may be horizontally displaced by up to 30 miles (48 kilometers) from the location of the underlying lightning strike.
Sprites are sometimes, but not always, preceded by a sprite halo — a broad, pancake-like region of transient optical emission centered at an altitude of about 47 miles (76 kilometers) above lightning, produced by weak ionization from transient electric fields of the same type that causes sprites.
Several years after their discovery they were named after the mischievous sprite “Puck” in Shakespeare’s Midsummer Night’s Dream.
Research at the University of Houston in 2002 indicates that some normal (negative) lightning discharges produce a sprite halo, the precursor of a sprite, and that every lightning bolt between cloud and ground attempts to produce a sprite or a sprite halo.
Photo The Waterboy
Photo Tucson Railfan
Blue jets differ from sprites in that they’re brighter, projecting from the top of the cumulonimbus above a thunderstorm usually in a narrow cone to the lowest levels of the ionosphere 25 to 30 miles (40 to 48 kilometers) above ground, and blue in color.
They were first recorded on a video taken from a space shuttle as it passed over Australia on October 21, 1989. Scientists at the Arecibo Observatory photographed a huge jet double reaching about 50 miles (80 kilometers) into the atmosphere above a thunderstorm over the ocean on September 14, 2001.
Five gigantic jets were observed between 35 to 45 miles (56 to 72 kilometers) in length over the South China Sea from Taiwan on July 22, 2002, with researchers likening the shapes to giant trees and carrots.
According to Arecibo scientists who performed research in 2001, the phenomenon is like an electron avalanche that can flood up toward the ionosphere or slide earthward, depending on the electric field direction, and claim that intense hail may trigger the avalanche. The field accelerates the electrons and slams them into air molecules which break down into ions and free electrons and emit light.
Photo DigitalTool @ Sardinia
Photo Mike Jones Photo
Elves often appear as dim, flattened, expanding glows around 250 miles (402 kilometers) in diameter that generally last for only 1 millisecond, occurring in the ionosphere 60 miles (97 kilometers) above the ground over thunderstorms, believed to have a red hue.
The light is generated by 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
They were first recorded on another shuttle mission off French Guiana on October 7, 1990.
Lightning has been triggered directly by human activity in several instances, such as flying aircraft — Apollo 12 was struck by lightening soon after takeoff — and thermonuclear explosions. It has also been triggered by launching lightning rockets carrying spools of wire into thunderstorms. The wire unwinds as the rocket ascends, providing a path for lightning with the bolts being typically very straight due to the path created by the wire.
Extremely large volcanic eruptions which eject gases and material high into the atmosphere can trigger lightning. The phenomenon was documented by Pliny The Elder during the AD79 eruption of Vesuvius, in which he perished.
Researchers have attempted to trigger lightning strikes since the 1970′s by means of ultra-violet lasers intended to protect rocket launching pads, electric power facilities, and other sensitive targets, which create a channel of ionized gas through which the lightning would be conducted to ground.
Playing the role of lightning rods, the beams sent from the laser make channels of ionized molecules known as “filaments”. Before the lightning strikes earth, the filaments lead electricity through the clouds.
Lightning requires the electrical breakdown of a gas, so it cannot exist in a visual form in the vacuum of space. It has been observed within the atmospheres of other planets, such as Venus, Jupiter and Saturn. Lightning on Venus is still a controversial subject after decades of research, but the most recent study in 2007 recorded by the spacecraft Venus Express with radio pulses confirmed lightning on Venus.
The area with the most lightning in the world lies deep in the mountains of eastern Democratic Republic of the Congo near the small village of Kifuka, which has an elevation of 3,200 feet (975 meters). Thunderbolts pelt this land with 158 bolts occurring over each square kilometer every year on average.
Singapore has one of the highest rates of lightning activity in the world. The city of Teresina in northern Brazil has the third-highest rate of lightning strikes on earth. The surrounding region is referred to as the Chapada do Corisco (“Flash Lightning Flatlands”).
Central Florida sees more lightning than any other area in the U.S. “Lightning Alley” — an area from Tampa to Orlando — receives as many as 50 strikes per square mile every year.
The Empire State Building is struck by lightning 23 times each year on average, and was once struck 8 times in 24 minutes.
Roy Sullivan held a Guinness World Record after surviving 7 different lightning strikes over 35 years.
In July 2007, lightning killed up to 30 people when it struck a remote mountain village Ushari Dara in northwestern Pakistan.
On 31 October 2005, 68 dairy cows, all in full milk, died on a farm at Fernbrook on the Waterfall Way near Dorrigo, New South Wales after being struck by lightning. 3 others were paralyzed for several hours but later made a full recovery. The cows were sheltering under a tree when it was struck by lightning and the electricity spread onto the surrounding soil killing the animals.
Lightning rarely strikes the open ocean, although some sea regions are lightning “hot spots.” Winter storms passing off the east coast of the United States often erupt with electrical activity when they cross the warm waters of the Gulf Stream — the Gulf itself has roughly as many lightning strikes as the southern plains of the USA.
Source: WikipediaTags:features lightening nature science