- Education and Science
The Several Types of Lightning
There is More Than What Meets the Eye and Ear
To really understand the phenomenon of lightning, one must appreciate the numerous forces that operate in generating these massive electrical discharges. The basic forces in operation are the solar wind, the geomagnetic field, the Van Allen belts, the ionosphere, the photoelectric effect, cosmic irradiation, quantum events and static charge buildup. There are several forms of lightning that occur in various manifestations and locations. These are;
cloud to earth (1)
earth to cloud (2)
cloud to cloud (3)
earth to earth (4, note: the site provides a disclaimer about authenticity)
ball lightning (5)
sprites and jets (6)
earth lights (7)
St. Elmo's Fire (8)
invisible lightning (9)
The earth exists in a perpetual state of an electric potential by altitude. This constantly varies over time and place and has various cycles. The ground beneath our feet is the same. The atmosphere and ground behave in a similar manner as a gigantic capacitor, gradually accumulating a charge only to release it all at once. To understand why lightning occurs in so many ways, let's look at some basics of the dynamic interaction between the solar wind, ioinization and the geomagnetic field.
The solar wind consists of ions and electrons propelled from the sun at varying velocities. During solar minimum periods, the “wind” is slower than during solar maximum and especially during a coronal mass ejection (CME). These winds always come toward the earth in part and on some occasions, a CME event engages the earth. The particle stream strikes the geomagnetosphere and much of it is directed away from the surface of the earth by the magnetic field. There are two places where the particles can gain access to the surface of the earth and that is near the geomagnetic poles. At these places, solar particles can get trapped in the earth's magnetic field and this is betrayed by the manifestation of the auroras. Depending on whether electrons or protons are involved, determines the direction in which trapped particles will spiral around the earth in the Van Allen Belts and ionosphere (10, 11). For the current era, where the north magnetic pole is mainly in the south, electrons are deflected and move from east to west. Protons will move from west to east. When geomagnetic reversal is completed, then the particles will reverse direction. The current period sees increasing chaos in the geomagnetic field, causing increasing localized particle eddies. This can produce serious local electrical disturbances, such as we see unfolding with wild weather in the current era.
The varying strength of the ionic wind from the sun also causes a variance in the frequency of electrostatic discharges (lightning) and indeed, during CME strikes, an increased tendency for earthquakes. The more intense the solar wind, the greater the electric potential from space to ground becomes. The electrostatic potential is averaged at about 2,000 volts per meter. Sometimes it is less and sometimes more. During electrostatic buildup to just prior to a lightning stroke, that dipole can increase up to 100,000 volts per meter. A more radical variance is true where the atmosphere is more “compressed” such as over mountain rages. At sea level, the potential is less extreme, unless a severe storm is present. Accumulated dust and moisture in the atmosphere and a low humidity level can increase the electrostatic gradient. Almost all of us have experienced lightning discharges in their various forms. Not all lightning is associated with thunderstorms. Some form as a result of pyroclastic type volcanic eruptions and nuclear blasts.
Everything You Wanted to Know About Lightning
Photos of Various Lightning Types
What form of Lightning is the Most Common?
The lightning most of us are familiar with, is the cloud to earth type. This results due to charge buildup between the tops and bottoms of massive thunderstorm clouds and from the bottom of these to the ground. Typically, the tops of massive clouds are positive, the bottoms negative and the ground positive. Sometimes, that is reversed. The cloud to ground lightning originates at the bottom layers of thunderstorm clouds. Electrostatic charge accumulates due to turbulence usually associated with a moving cold front, until the point where the lightning discharge balances the electrical dipole of cloud and earth. The lightning quickly forms along the path of least resistance to a high point on the ground like a tree or building. A positive leader forms from that ground point toward the down stroke to make the electrical connection. Often, lightning will branch as electrical potential seeks balance in many places at once. There are instances where the bolt will flicker rapidly as charges sometimes will not achieve neutrality on the first strike. During a thunderstorm, if you find your hair beginning to stand on end, this is a clear and present sign to seek immediate cover.
Earth to cloud lightning is relatively rare compared to cloud to cloud and cloud to earth, but it happens and it has been filmed. The typical cloud to earth branches as it leaves the cloud. The earth to cloud branches as it reaches up to the clouds. The principle is much the same as cloud to earth, but the charge is reversed so that the electron flow occurs from the ground. This could presage an earthquake or may be a sign of human generated electrical activity.
Cloud to cloud lightning manifests when charge difference is most pronounced from one region of the atmosphere to another, such as can occur in regions of radical temperature difference and moisture conditions. These strikes appear to slowly branch out from one part of the cloud cover to another. There may or may not be associated thunder. This lightning is visible over large distances, especially at night and accounts for much of the lack of sound.
One of the rarest forms of lightning is earth to earth. Usually, it is associated with an ash volcanic eruption or pyroclastic flow. Sometimes a massive forest fire or firestorm will create the right conditions. Sometimes, it is associated with man made activity. Again, if a dipole is set up in the ground from one region to another, such lighting strikes can occur even on a sunny day without clouds. If pollution levels are high, it increases the risk of such ground to ground strikes. The existence of large and powerful transformer parks also promote such lightning.
Ball lightning is one of the strangest and least understood forms of lightning. It is often, but always produced in an electrical storm. Some experimenters claim to be able to produce it at will. However, the results are unlike ball lightning that can float, pass through glass and solid walls unhindered and without dissipating. This phenomenon should not be stable according to traditional theory, but they do and can persist for extended periods. Sometimes it fades away and sometimes explodes with a horrific bang. In addition, it appears to be immune from the influence of magnetic fields. What it is remains a deep mystery.
Sprites form high in the outer atmosphere above the highest thunderheads and are now known to be associated with electrical discharges further down in the clouds and atmosphere. Unless you have the right view, a good view is hard to attain, but they have been photographed. They appear as a red and conic diffuse glow with the pointed end toward the cloud cover. Sometimes they appear to be blue. They have been seen to descend to the cloud tops, but also to ascend up into near space. The later are known as jets. They are thought to be electrons or protons captured by the geomagnetosphere being drawn into the lower atmosphere by an electrical imbalance.
Earth lights are often mistaken for UFOs or flying saucers. They are not and are now considered most closely related to ball lightning. They are electrical discharges from the earth, especially associated with imminent earthquake activity.
St. Elmo's fire is a peculiar electrostatic glow that can form inside or outside any for of aircraft. It is thought to be a natural form of fluorescence in an electrically charged atmosphere. That it should occur specifically around aircraft suggests that the flying vehicle is serving as some sort of receiver that works in a process not dissimilar to what happens in artificial fluorescence. St. Elmo's fire, though frightening to most who are unfamiliar with it, is usually harmless.
The most dangerous form of lightening, is also thankfully, relatively rare. Invisible lightning is not seen nor heard. It occurs most frequently in the high atmosphere. It presents the greatest danger to anyone who is flying. A strike is always fatal. Invisible lightning is generated by relativistic gamma rays that create an ionized path when entering the atmosphere. As the rays progress, they decay before most of them reach the ground. A complex shower of ionized particles result. Should a shower of these pass through a human body in flight, the rays create an intensely ionized and complex path through the body that create a fatal dose of radiation. The affected individual may live for some time to experience a death by severe irradiation. Invisible lightning may or may not betray its presence by a flash of a deep violet glow. It is impossible to predict such a strike, but it is thought that the originate in gamma ray bursts. Fortunately, the earth's magnetic field, weakening though it is, and the atmosphere prevent most invisible lightning from ever reaching the ground.
Today, we have enough understanding to tap and direct lightning by ionizing the atmosphere with a powerful laser. This forms a channel which natural electrical forces can be controlled and directed. Massive amounts of power can be tapped instantaneously as a result. We have yet to devise a way to store such a surge on the order of milliseconds.
to 9, except 4. http://en.wikipedia.org/wiki/Lightning