Learn / Glossary
air discharge
A form of lightning discharge probably similar to a cloud discharge in which the lightning channel propagates away from a cloud charge center into apparently clear air where it terminates. Thus, cloud charge is moved away from its original location and space charge of opposite sign outside the cloud may be neutralized.
atmospheric electric field
A quantitative term, denoting the electric field strength of the atmosphere at any specified point in space and time. In areas of fair weather, the atmospheric electric field near the earth’s surface typically is about 100 volts per meter and is directed vertically in such a sense as to drive positive charges downward to the earth. In areas of fair weather this field decreases in magnitude with increasing altitude, falling for example, to only about 5 volts per meter at an altitude of about 10 km. Near thunderstorms, and under clouds of vertical development, the surface electric field varies widely in magnitude and direction, usually reversing its direction immediately beneath active thunderstorms. In areas of minimum local disturbance, a characteristic diurnal variation of electric field strength is observed. This variation is characterized by a maximum which occurs at about 19 hr UTC for all points on the earth, and is now believed to be produced by thunderstorms which, for geographic regions, are more numerous for the world as a whole at that universal time than at any other. It is now believed that thunderstorms, by replenishing the negative charge to the earth’s surface, provide the supply current to maintain the fair-weather electric field in spite of the continued flow of the air-earth current that tends to neutralize that field.
During fair weather, a potential difference of 200,000 to 500,000 volts exists between the earth’s surface and the ionosphere, with a fair weather current of about 2×10-12 Amperes/meter2. It is widely believed that this potential difference is due to the worldwide distribution of thunderstorms.
Present measurements indicate that an average of almost 1 Ampere of current flows into the stratosphere during the active phase of a typical thunderstorm. Therefore, to maintain the fair weather global electric current flowing to the surface, one to two thousand thunderstorms must be active at any given time, producing on the order of 100 flashes per second. While present theory suggests that thunderstorms are responsible for the ionospheric potential and atmospheric current for fair weather, the details are not fully understood.
atmospheric transients
The atmospheric transient is a secondary effect resulting from varying electrostatic fields generated by thunderstorms and caused by discharges from direct lightning strikes. Any conductors suspended above the earth and immersed within an electrostatic field will be charged to that same voltage potential related to the object’s height (i.e. height times the field strength) above local grade (see electrostatic field). As discharges (lightning strokes) occur nearby, the electrostatic field changes, sending voltage transients searching for a path to earth, along these conductors. Unless the path is properly protected, it will damage sensitive electric and electronic equipment along the way.
ball lightning
A relatively rarely seen form of lightning, generally consisting of an orange, reddish, or dazzling blue-white ball a few cm to 30 cm in diameter and of moderate luminosity, which may move up to 1 m/s horizontally with a lifetime of a second or two. Hissing noises sometimes emanate from such balls, and they can explode noisily or disappear noiselessly. The physical nature of ball lightning is not understood. Similar phenomena occasionally occur in high-current industrial equipment, but the conditions for such production are not reproducible.
bead lightning
A particular visual variation of the end of a normal lightning flash where periodic sections of the channel appear to die out slowly because they have greater radius and hence lose heat more slowly, are seen end-on, or for other unknown reasons.
bound charge
A build up of induced or static charges within the products held in metal storage containers (for example petroleum within storage tanks, or ammunition within ammunition containers). When lightning strikes nearby, because the container is made of metal and is usually well grounded, any induced charges within the metal container are instantly discharged. However, because the products within the containers may be partially insulated from the metal container itself, they retain their charge, called the bound charge. This bound charge will dissipate over time, or instantly if properly grounded, however, if not properly grounded and if intense enough, it will cause arcing (sparking) between the floating roof and the tank wall or between the ammunition and the container. This can result in explosions and fires.
breakdown
The process by which electrically-stressed air is transformed from an insulator to a conductor. Breakdown involves the acceleration of electrons to ionization potential in the electric field imposed by the thundercloud, and the subsequent creation of new electrons which avalanche and expand the scale of enhanced conductivity. Breakdown precedes the development of lightning or higher current-carrying processes during lightning flashes.
charge separation
The physical process causing cloud electrification. The process can include particle collisions with selective charge transfer and particle capture of small ions at the particle scale. The process can include gravity-driven differential particle motions and convective transport of charged air parcels at the cloud scale.
charge transfer system
A charge transfer system (also called a streamer delaying system) consists of installing a suitable array composed of a multitude of well-grounded sharp conductors around the area to be protected. The system diverts lightning away from the protected area by forming a space charge above the charge Dissipation Array. The space charge is a collection of charged particles (ions) in air that lowers the local electrical field. In the charge transfer system, a space charge is generated by point discharge from the sharp conductors. Once formed, the space charge reduces the electric field locally above the protected area.
cloud electrification
The process by which clouds become electrified. This process separates positive and negative electric charge and develops potential differences occasionally sufficient to produce lightning.
cloud electrical shadow
See induced ground charge
cloud flash
A lightning discharge occurring between a positively charged region and a negatively charged region, both of which may lie in the same cloud. The most frequent type of cloud discharge is one between a main positive-charged region and a main negative-charged region. Cloud flashes tend to outnumber cloud-to-ground flashes. In general, the channel of a cloud flash will be wholly surrounded by cloud. Hence, the channel’s luminosity typically produces a diffused glow when seen from outside the cloud and this widespread glow is called “sheet lightning”, also called “intra-cloud flash” and “cloud-to-cloud flash”. There are roughly 5 to 10 times as many cloud-to-cloud flashes as there are cloud-to-ground.
cloud-to-ground flash
A lightning flash occurring between a charge center in the cloud and the ground. On an annual basis, negative charge is lowered to ground in about 95% of the flashes; in the remaining 5% of the flashes a positive charge is lowered to ground. This type of lightning flash, which can be contrasted with an intra-cloud flash or cloud-to-cloud flash, consists of one or more return strokes. The first stroke begins with a stepped leader followed by an intense return stroke which is the principal source of luminosity and charge transfer. Subsequent strokes begin with a dart leader followed by another return stroke. Most of the strokes use the same channel to ground. The time interval between strokes is typically 40 milliseconds.
Over the continental 48 states of the United States, an average of 20,000,000 cloud-to-ground flashes have been detected every year since the lightning detection network covered the entire continental US in 1989. In addition, about half of all flashes have more than one ground strike point, so at least 30 million points on the ground are struck on the average each year in the U.S. (approximately 19 direct strikes per square kilometer per year).
convection
In atmospheric electricity, a process of vertical charge transfer by transport of air containing a net space charge, or by motion of other media (for example, rain) carrying net charge. Eddy diffusion of air containing a net charge gradient may also yield a convection current.
corona
A faint glow enveloping the high-field electrode in a corona discharge, often accompanied by streamers directed toward the low-field electrode.
corona current
The electrical current that is equivalent to the rate of charge transferred to the air from a pointed object (or array of objects) experiencing corona discharge. Ordinarily, a corona forms upon terrestrial objects at times of thunderstorm passage and constitutes a transfer of negative charge from air to object.
corona discharge
A luminous, and often audible, electric discharge that is intermediate in nature between a spark discharge (with, usually, its single discharge channel) and a point discharge (with its diffuse, quiescent, and non-luminous character). It occurs from objects, especially pointed ones, when the electric field strength near their surfaces attains a value near 100,000 volts per meter. Aircraft flying through active electrical storms often develop corona discharge streamers from antennas and propellers, and even from the entire fuselage and wing structure. So-called precipitation static results. It is seen also, during stormy weather, emanating from the yards and masts of ships at sea. Known among mariners as St. Elmo’s Fire. It is also called a corporant.
counter-leader
See return stroke and streamer
dart leader
The leader which typically initiates each succeeding stroke of a multiple-stroke flash lightning after the first stroke. The first stroke is initiated by a stepped leader. The dart leader derives its name from its appearance on photographs taken with streak cameras. The dart leader’s brightest luminosity is at its tip which is tens of meters in length, propagating downward at about 10^7 m/s. In contrast to stepped leaders, dart leaders do not typically exhibit branching because the pre-established channel’s low gas density and residual ionization provide a more favorable path for this leader than do any alternative ones.
dart-stepped leader
See leader
earth current transient
The earth current transient is the direct result of the neutralization process that follows stroke termination. The process of neutralization is accomplished by the movement of the charge along or near the earth’s surface from the location where the charge is induced to the point where the stroke terminates. Any conductors (including electrical wiring, piping and plumbing) buried in the earth within or near the charge will provide a more conductive path from where it was induced to the point nearest the stroke termination. This induces a voltage on those conductors. Since the discharge process if very fast (20 microseconds) and the rate of rise to peak is as little as 50 nanoseconds, this induced transient voltage, although short, will be very high.
electric charge
A fundamental property of matter exhibiting two states, positive and negative, that results in the action of electric forces in the presence of an electric field. These two states were identified and named by Benjamin Franklin. The positive charge on the proton and the negative charge on the electron represent the fundamental charge, 1.602 x 10^-19 coulombs (inversely, therefore, a coulomb can be defined as the charge on 6.24 x 10^ +18 electrons).
electric discharge
The flow of electricity through a gas, resulting in the emission of radiation which is characteristic of the gas and of the intensity of the current.
electrostatic field
A static field of electrical energy. The greater the difference between the electrical charge in a thunderstorm cloud and that of the ground below, the greater is the potential for a lightning event. The IMPACT ALDF and Electric Field Mill measure the difference between the ground level electric field and the above-ground electric field to estimate the potential of a lightning strike.
The electrical force exerted on a unit’s positive charge placed at a given point in space. The electric field strength is expressed, in the m.kg.s. (meters/kilograms/seconds) and in the SI (System International) systems of electrical units, in terms of volts per meter and is a vector quantity. The electric field strength of the atmosphere is commonly referred to as the atmospheric electric field and is usually expressed in kilo-volts per meter (for example: 10 kV/m or 100 kV/m).
electromagnetic pulse (EMP)
The electromagnetic pulse is a secondary effect from a direct lightning stroke and is the result of the transient magnetic fields that form from the flow of intense transient current through the lightning channel.
field changes
The rapid variations of the electrical field at the earth’s surface, beneath, within and above thunderclouds. Used to determine quantitative estimates of the charge transferred during a lightning discharge, heights of the charge centers, and many other features of thunderclouds.
flash
The entire cloud-to-ground or ground-to-cloud electrical atmospheric discharge is called a flash. A flash may also occur within a cloud, between clouds, or between clouds and earth. A flash includes one or more strokes and high current pulses called return strokes. Duration of a flash is usually less than one second, and typically has a duration of half a second.
forked lightning
The common form of cloud-to-ground discharge always visually present to a greater or lesser degree which exhibits downward-directed branches from the main lightning channel. In general, of the many branches of the stepped leader, only one is connected to ground defining the primary, bright return stroke path, and the other incomplete channels decay after the ascent of the first return stroke.
ground-to-cloud discharge
A lightning discharge in which the original leader process starts upward from some object on the ground; the opposite of the much more common cloud-to-ground discharge. Ground-to-cloud discharges most frequently emanate from tall mountain peaks or very tall structures which, and having equipotential with the earth, can exhibit the strong field intensities near their upper extremities necessary to initiate leaders. Upward-initiated flashes are relatively rare.
heat lightning
Non-technically, the luminosity observed from ordinary lightning too far away for its thunder to be heard. Since such observations have often been made with clear skies overhead, and since hot summer evenings particularly favor this type of observation, there has arisen a popular misconception that the presence of diffused flashes in the apparent absence of thunderclouds implies that lightning is somehow occurring in the atmosphere merely as a result of excessive heat.
induced ground charge
When a thunderstorm with electrified clouds (see charge separation) moves over an area, it induces a similar charge intensity of opposite polarity upon the ground surface below it. As the storm intensifies, so does the magnitude of this induced ground charge.
leader
The electric discharge which initiates each return stroke in a cloud-to-ground lightning discharge. It is a channel of high ionization which propagates through the air by virtue of the electric breakdown at its front produced by the charge it lowers. The stepped leader initiates the first stroke in a cloud-to-ground flash and establishes the channel for most subsequent strokes of a lightning discharge. High-speed photographs show that leader steps are typically one (1) microsecond in duration, tens of meters in length, and that the pause time between steps is 20 to 50 microseconds.
The dart leader initiates most subsequent strokes. Dart-stepped leaders begin as dart leaders and end as stepped leaders. The initiating processes in cloud discharges are sometimes also called leaders but their properties are not well measured.
lightning
Lightning is a transient, high-current electric discharge whose path length is measured in kilometers. The most common source of lightning is the electric charges separated in ordinary thunderstorm clouds (cumulonimbus).
There have been limited studies of the electrical properties of stratus, stratocumulus, cumulus, nimbostratus, altocumulus, altostratus and cirrus clouds. Any of these cloud types can potentially cause lightning, or some related form of electrical discharge, as can snowstorms, the clouds above volcanoes, and other turbulent environments such as dust storms.
Well over half (over 90%) of all lightning discharges occur within the thunderstorm cloud and are called intra-cloud discharges. The usual cloud-to-ground lightning, sometimes called streaked or forked lightning, has been studied more extensively than other lightning forms because of its practical interest, as the cause of injuries and death, disturbances in power and communicating systems, and the ignition of forest fires, and because lightning channels below cloud level are more easily photographed and studied with optical instruments. Cloud-to-cloud and cloud-to-air discharges are less common than intra-cloud or cloud-to-ground lightning. All discharges other than cloud-to-ground are often lumped together and called cloud discharges.
Lightning is a self-propagating and electrode-less atmospheric discharge that transfers through the induction process the electrical energy of an electrified cloud into electrical charges and current in its ionized and thus conducting channel. Positive and negative leaders are essential components of the lightning. Negative cloud-to-ground (CG) flashes probably account for about 90% of the CG discharges worldwide, and less than 10% of lightning discharges are initiated by a downward-moving positive leader.
Only when a leader reaches the ground, the ground potential wave (return stroke) affects the lightning process. Natural lightning starts as a bidirectional leader although, at different stages of the process, unidirectional leader development can occur. Artificially triggered lightning starts on a tall structure or from a rocket with a trailing wire. Most of the lightning energy goes into heat, with smaller amounts transformed into sonic energy (thunder), radiation, and light. Lightning, in its various forms, is known by many names such as the common streak lightning, forked lightning, sheet lightning, heat lightning and the less common air discharge; also, the rare and mysterious ball lightning and rocket lightning. For some detailed explanation of lightning processes, see lightning discharge and related terms.
An abrupt, discontinuous natural electric discharge in the atmosphere. Lightning produces a sound wave that is heard as thunder.
An important effect of worldwide lightning activity is the net transfer of negative charge from the atmosphere to the earth. This fact is of great importance in one problem of atmospheric electricity, the question of the source of the supply current. Existing evidence suggests that lightning discharges occurring sporadically at all times in various parts of the earth, perhaps 100 per second, may be the principal source of negative charge that maintains the earth-ionosphere potential difference of several hundred thousand volts in spite of the steady transfer of charge produced by the air-earth current. However, there is also evidence that point discharge currents may contribute to this more significantly than lightning.
Many bad things happen when lightning strikes, resulting in direct and secondary effects. Direct effects include: fires, high voltage and high current surges along conductors (along lightning rods to grounding rods, and along any electrically or metallically connected equipment), and death. (See lightning damage). Secondary effects include intense electromagnetic pulses (EMP), earth current transients, atmospheric transients and bound charges. (See secondary effects.)
lightning channel
The irregular path through the air along which a lightning discharge occurs. The lightning channel is established at the start of a discharge by the growth of a leader, which seeks out a path of least resistance between a charge source and the ground or between two charge centers of opposite sign in the thundercloud or between a cloud charge center and the surrounding air or between charge centers in adjacent clouds. (See also cloud-to-ground, intra-cloud, and air discharges.)
lightning damage
Cloud-to-ground lightning can kill or injure people by direct or indirect means. The lightning current can branch off to a person from a tree, fence, pole, or other tall object. It is not known if all people are killed who are directly struck by the flash itself. In addition, flashes may conduct their current through the ground and then through a person after the flash strikes a nearby tree, antenna, or other tall object. The current may also travel through power or telephone lines, or plumbing pipes to a person who is in contact with an electric appliance, telephone, or plumbing fixture. Objects can be struck directly and this impact may result in an explosion, burn, or total destruction as a result of the intense transient currents of up to 300 kiloAmperes. Or, the damage may be indirect (see secondary effects) when the current passes through or near them. Sometimes, current may enter a building and transfer through wires or plumbing and damage everything on its path to earth. Similarly, in urban areas, it may strike a pole or tree and the current then travels to several nearby houses and other structures and enter them through wiring or plumbing.
lightning discharge
The series of electrical processes taking place typically within one second by which charge is transferred along a discharge channel between electric charge centers of opposite sign within a thundercloud (intra-cloud discharge) between a cloud charge center and the earth’s surface (cloud-to-ground discharge or ground-to-cloud discharge), within two different clouds (inter-cloud or cloud-to-cloud discharge), or between a cloud charge and the air (air discharge). It is a very large-scale form of the common spark discharge. These lightning discharges could be either “Negative” or “Positive” (see polarity). A single lightning discharge is called a lightning flash.
lightning flash
The total observed lightning discharge generally has a duration of less than one second. A single flash is usually composed of many distinct luminous events (strokes) that often occur in such rapid succession that the human eye cannot resolve them.
lightning stroke
In a cloud-to-ground discharge, a leader plus its subsequent return stroke. In a typical case, a cloud-to-ground discharge is made up of three or four successive lightning strokes, most following the same lightning channel.
lightning suppression
Procedures to prevent the occurrence of lightning. Seeding below cloud base with 10 cm fiber chaff in a Colorado study resulted in corona discharges that caused a discharging current to flow within developing or active thunderstorms. Electric fields below thunderstorms seeded with chaff decayed much faster than electric fields below non-seeded storms, and chaff seeding of existing thunderstorms greatly reduced cloud-to-ground flashes in non-seeded storms. Recent evidence suggests that chaff releases may result in a significant decrease in downwind cloud-to-ground lightning. Another experimental approach is to use lasers to discharge lightning in an overhead cloud in order to divert the flash from striking people or highly sensitive equipment on the ground; more research is needed to make this a realistic method of lightning suppression. In the 1960’s, seeding with silver iodide was considered in order to produce an excess of ice crystals to cause numerous coronal discharges within the thunderstorm and reduce the need for the flash to reach the ground, but the test results were complex and difficult to identify. Electric space charges were released into the atmosphere from a network of high-voltage wires on the ground to produce corona discharge, but a field test showed minimal effects on suppressing lightning. However, notable documented success has been achieved using charge transfer systems, which dissipate some of the ground charge into the air creating local space charges and locally reduces the electrostatic field. Since lightning always prefers to follow a path of least resistance, lightning strokes terminate in nearby areas with a higher ground charge and within higher electrostatic field.
negative lightning discharge
A cloud-to-ground discharge which begins in a negative region of the cloud and effectively lowers some tens of coulombs of negative charge to the earth. Over 90% of all cloud-to-ground lightning strikes are of this type. (See polarity.)
peak current
The maximum current measured in kilo Amperes (kA) of the lightning discharge is typically in the 20 to 30 kA range with a maximum of 310kA.
polarity
Lightning may be of a negative or positive polarity depending on the direction of the current flow between a cloud and the ground. Most lightning flashes are negative in polarity − negative cloud to positive ground. Broadly defined polarity describes voltage as positive or negative in reference to the originating point.
positive lightning discharge
A rare cloud-to-ground discharge which begins in a positive region of the cloud (from one of the small localized regions, or an inverted large region) and terminates in a temporarily induced negative area on the earth below.
return stroke
The current pulses that transfer charge along highly luminous channels between cloud and ground during a cloud-to-ground stroke
The intense luminosity which propagates upward from earth-to-cloud base in the last phase of each lightning stroke of a cloud-to-ground discharge. In a typical flash, the first return stroke ascends as soon as the descending stepped leader makes electrical contact with the earth, often aided by short ascending ground streamers. The second and all subsequent return strokes differ only in that they are initiated by a dart leader and not a stepped leader. It is the return stroke which produces almost all of the luminosity and charge transfer in most cloud-to-ground strokes. Its great speed of ascent (about 1 X 10^8 m/sec) is made possible by residual ionization of the lightning channel remaining from passage of the immediately preceding leader, and this speed is enhanced by the convergent nature of the electrical field in which channel electrons are drawn down toward the ascending tip in the region of the streamer’s electron avalanche. Current peaks as high as 300,000 Amperes have been reported, and values of 30,000 Amperes are fairly typical. The entire process of the return stroke is completed within a few tens of microseconds, and even most of this is spent in a long decay period following an early rapid rise to full-current value in only a few microseconds. Both the current and propagation speed decrease with height. In negative cloud-to-ground flashes the return stroke deposits the positive charge of several coulombs on the preceding negative leader channel, thus charging earth negatively (or neutralizing a portion of the induced ground charge). In positive cloud-to-ground flashes, the return stroke deposits the negative charge of several tens of coulombs on the preceding positive leader channel, thus lowering positive charge to ground (or neutralizing a portion of the induced ground charge). The entire return stroke process is completed in a few tens of microseconds. In negative cloud-to-ground flashes, multiple return strokes are common. Positive cloud-to-ground flashes, in contrast, typically have only one return stroke. The return streamer of cloud-to-ground discharges is so intense because of the high electrical conductivity of the ground, and hence this type of streamer is not to be found in air discharges, cloud discharges, or cloud-to-cloud discharges.
stroke
A singular electrical discharge or high current pulse identified as a flash or as one of several strokes (usually 3 or 4) that make up a flash of lightning. The transfer of electrical charge may be within or between clouds or between clouds and earth.
Each stroke lasts about a millisecond, and the separation between strokes is typically several tens of milliseconds. Lightning often appears to “flicker” because the human eye can just resolve the individual pulses of luminosity that are produced by each stroke.
The second stage of a lightning event is called a “stroke.” It creates a discharge of electrical energy, along with a blinding white flash. These blinding white flashes are followed by the crash of thunder due to the supersonic expansion of the air as it heats up. The first leader/stroke is often followed by another leader/stroke combination within a few hundredths of a second. Up to 20 or more such sequences can occur, creating the flickering appearance of lightning. Strokes can connect to the ground at more than one location, up to seven (7) kilometers (about 4.3 miles) apart! The combined strokes occurring in a second around the first stroke location are called a “flash”.
ribbon lightning
Ordinary cloud-to-ground lightning that appears to be spread horizontally into a ribbon of parallel luminous streaks when a very strong wind is blowing at right angles to the observer’s line of sight. Successive strokes of the lightning flash are then displaced by small angular amounts and may appear to the eye or camera as distinct paths. The same effect is readily created artificially by rapid transverse movement of a camera during film exposure.
rocket lightning
A form of cloud discharge, generally horizontal and at cloud base, whose luminous channel appears to advance through the air with visually resolvable speed, often intermittently.
secondary effects
Lightning activity (direct lightning strikes resulting in lightning discharges) within close proximity to wiring, plumbing, electrical and electronic equipment generate destructive and disruptive secondary effects. Secondary effects include intense electromagnetic pulses (EMP), earth current transients, atmospheric transients and bound charges.
sheet lightning
A diffused, but sometimes fairly bright, illumination of those parts of a thundercloud that surround the path of a lightning flash particularly a cloud discharge or cloud-to-cloud discharge. Thus, sheet lightning is no unique form of lightning but only one manifestation of ordinary lightning types in the presence of obscuring clouds.
space charge
Any net electrical charge that exists in a given region of space. In electronics, this usually refers to the electrons in the space between the filament and plate of an electron tube. In atmospheric electricity, space charge refers to a preponderance of either negative or positive ions within any given portion of the atmosphere. A net positive space charge is found in fair weather at all altitudes in the atmosphere, and is largest near the earth’s surface. The general downward flux of this positive space charge is known as the air-earth conduction current.
stepped leader
The initial leader of a lightning discharge; an intermittently advancing column of high ionization and charge which establishes the channel for a first return stroke. The peculiar characteristic of this type of leader is its step-wise growth at intervals of about twenty to fifty to one hundred microseconds. The velocity of growth during the brief intervals of advance, each only about one microsecond in duration, is quite high (about 5 x 10^7 m/s), but the long stationary phases reduce its effective speed of downward propagation to only about 2 to 5 x 10^5 m/s. To help explain its mode of advance, the concept of a pilot streamer was originally suggested but has been supplanted by analogy to recent work on long laboratory sparks.
A fully developed stepped leader can effectively lower the cloud charge by 10 coulombs or more of negative charge toward the ground in tens of milliseconds. Step leaders have peak pulse currents of at least 1 kA.
streak lightning
Ordinary lightning, of a cloud-to-ground discharge that appears to be entirely concentrated in a single, relatively straight lightning channel
streamer
A sinuous channel of very high-ion density which propagates itself though a gas by continual establishment of an electron avalanche just ahead of its advancing tip. In lightning discharge the stepped leader, dart leader, counter-leader and return stroke all constitute special types of streamers.
subsequent stroke
The strokes that occur after the first stroke of a flash.
thunder
Sound is generated along the length of the lightning channel as the atmosphere is heated by the electrical discharge to the order of 20,000 degrees C (3 times the temperature of the surface of the sun). This compresses the surrounding clear air producing a shock wave which then decays to an acoustic wave as it propagates away from the lightning channel.
Although the flash and resulting thunder occur at essentially the same time, light travels at 186,000 miles in a second, almost a million times the speed of sound. Sound travels at the relatively snail pace of one-fifth of a mile in the same time. Thus the flash, if not obscured by clouds, is seen before the thunder is heard. By counting the seconds between the flash and the thunder and dividing by 5, an estimate of the distance to the strike (in miles) can be made.
thunderbolt
In mythology, a lightning flash accompanied by a material bolt or dart; this is the legendary cause of the damage done by lightning. It is still used as a popular term for a lightning discharge accompanied by thunder.
zigzag lightning
Ordinary lightning of a cloud-to-ground discharge that appears to have a single, but very irregular, lightning channel.
