Scientists have learned some facts about lightning from pictures. Definition: Lightning stroke is the direct discharge of an electrical charge between the atmosphere and the object of earth. Lightning return stroke speed is one of the main parameters in lightning modeling, so as in evaluating lightning-induced effects [6]. Previous calculation methods generally use an average value for the return stroke velocity along a lightning channel. EMC, 33, 351-357, 1991). Wind blows the charged channel so position shifts between return strokes. The stroke channel of a lightning bolt is very narrow—perhaps as little as half an inch (1.25 centimeters). Graupel is between two and five millimetres across, and occurs when super-cooled water freezes on the outside of, say, a snowflake. Electron velocity in the partially ionized channel is non relativistic [2]. Once the step leader makes contact with a streamer, the negative charge that has accumulated along the leader channel flows rapidly to ground. return stroke) to shoot from the ground to the cloud. Lightning is fun to watch. Lightning Return-Stroke Current Waveforms Aloft, from Measured Field Change, Current, and Channel Geometry Three-dimensional reconstructions of six rocket-triggered lightning channels are derived from stereo photographs. The results show that the peak time derivative of the currents in lightning strokes terminating on poorly conducting ground is significantly lower than the case of highly conducting ground. This causes the characteristic blue-white colour of a lightning bolt. It happens so fast that you may not easily discern the direction of propagation. The stepped leader, moving at a velocity of about 200 miles per hour, takes about one-hundredth of a second to travel from the cloud to earth." The movement of the charge starts at the point of contact and rapidly works its way upward as charge is drained from the channel  It's carrying about 10-100 amps of current. The maximum field derivatives during return strokes range from 5 to 75 V/m(μs) -1 with a mean of 29 V/m(μs) -1 when normalized to a distance of 100 km. Please Contact Us. The reason why that's bad, is that (according to this) the return stroke is 1,000 times faster than the original.This isn't good since no one would get hit by the return stroke But it's kind of invisible because it's moving so fast. The lightning return stroke current is an important parameter for the evaluation of the efiect of lightning on power lines as the lightning can in°uence a power network both directly and indirectly. Your information is handled in accordance with the ABC Privacy Collection Statement. Results show that for a lightning stroke without an upward connecting leader, the large lightning stroke current is firstly generated at the channel base and then propagates upward as its amplitude decreases. The super-cooled water droplets and hail are much smaller and lighter, so the strong up-currents of wind inside the thundercloud carry them upwards. The expression "lightning return-stroke model" is generally used to describe a specification of the time- and height-dependent current in the rerum-stroke channel to make possible the calculation of resultant remote electromagnetic fields [Rakov and Uman, 1998]. Via a complicated process, they become positively charged, while the graupel becomes negatively charged. What happens next is the return stroke—which is much more powerful and yet kind of invisible. Many have asked, "Why don't we capture this awesome power, and use it to power our industries and boil our kettles?". Each step occurs in less than one-millionth of a second, and the time between each step is about one fifty-millionth of a second. 16, No. First, there's air moving rapidly upwards, and second, there are freezing temperatures (ranging between 15 and 25 degrees below zero). For another, lightning B is a single return stroke CG discharge process. Source: Leteinturier, C., J.H. CG return strokes usually have larger currents that make stronger signals that are easier to … This stroke was the third of eight otherwise negative strokes in a triggered lightning flash initiated at the Kennedy Space Center, Florida. Tom A flash of lightning is just 1 to 2 inches wide, but it generates a massive amount of electricity that is equal to 300 million volts, or 30,000 amps. of Florida site. iv First, we build a modeling environment for each function, which can be described as parameter estimation system. One-and-a-half billion lightning bolts sounds like a lot, but only about one quarter of them get to the ground. The air surrounding these pauses is again ionized and the leader in this way reaches the earth (Fig.1.6(c)).Once the stepped leader has made contact with the earth it is believed that a power return stroke(Fig. Although the lightning return-stroke current, measured at the CN Tower, is simulated using the Pulse function and Heidler function, the simulation of the CN Tower lightning current derivative signal is considered using the derivative of the Pulse and Heidler functions. The effects of channel branches on return-stroke radiated fields have been theoretically studied by Le Vine and Meneghini [1978a], Vecchi et al. The numerous pulsing return strokes occur in rapid succession, making the lightning bolt appear to flicker on and off. Some lightning flashes are made up of as many as 25 or more lightning bolts (strokes). Figure 2 shows the various components of a lightning flash including the stepped leader, positive streamers, the return stroke, and three dart leaders/return stokes. The fast transitions found on the initial portion of return-stroke fields have 10–90% risetimes ranging from 40 to 200 ns, with a mean of 90 ns. We have investigated the roots of the modern concepts used to describe return stroke related phenomena and illustrated their developments and deviations from the original idea. Concepts of lightning return stroke models Abstract: Return stroke models have been reviewed according to the assumptions they make and their underlying concepts. Lightning strikes Sydney Tower during a storm. This lightning flash occurred near the campus of the University of Alabama in Huntsville on May 22, 2012. The return flow (positive charge) moves upward more slowly. A bullet fired from an AK-47 is about 26 mm long and moves at about 700 millimeters every millisecond. Lightning Discharges Yanan Zhu 1,*, ... with a single PB pulse train and NLDN-reported first-return-stroke (RS) peak current ≥50 kA were selected for detailed analysis. While the downstroke of the lightning strike moves at about 200 kilometres a second, the upward return stroke zips along at 100,000 kilometres a second—about one third of the speed of light. For a moment after the initial return stroke, the channel remains conductive and can be a favored path for subsequent downward leaders. On the transmission line model for lightning return stroke representation, Geophys. It is important to note that Liang et al. Evolution of the lightning stroke. This channel segment corresponds to the time when the initial peaks of the channel-base current (the typical 10-90% risetime of subsequent return-stroke currents is 0.3 to 0.6 µs (see Fisher et al., 1993, Fig. The third type of water, the graupel, is larger and heavier than the two other types, and either stays where it is in the strong updraft or falls to the bottom of the cloud. The "leader", the first stroke of a lightning discharge, actually proceeds in steps -- lengthening by about 30 meters at a time, taking about a microsecond (one millionth of a second) to do each step. Eventually, over about a 20,000th of a second, a lightning strike stutters its way towards the ground in a series of steps. Additionally, it is shown how a return stroke model could be utilized to study the effect of ground conductivity on the return stroke current. Lett., 30(24), 2294, doi:10.1029/ 2003GL018407, 2003. It take a unique series of weather factors to create the awesome power of lightning, and when it strikes it comes to earth with 1,000 times more energy than a household electrical system and with more heat than the sun. Above, branches extending deep into the cloud tap into areas of electrical charge. All propagation speeds were evaluated over 850 m of channel near ground and have an error estimate of 10‐15%. The arithmetic mean values of PB pulse train duration, PB-RS interval, and PB/RS pulse peak ratio were 2.7 ms, 8.8 ms, and 0.15, respectively. These reconstructed channels are used to infer the behavior of the current in return strokes above the ground from current waveforms measured at the channel base and … of Electrical Engineering, Indian Institute of … Lightning Return-Stroke Current Waveforms Aloft, from Measured Field Change, Current, and Channel Geometry Three-dimensional reconstructions of six rocket-triggered lightning channels are derived from stereo photographs. They move so fast that your eyes only see one flash! bead lightning. The return stroke is the very bright visible flash that we see as lightning, caused by the rapid discharge of electricity. Now this downstroke—impressive as it is—is just the warmup for the main event. Third, and again a bit unexpected, there are quite large blobs of soft hail with the unusual name of "graupel". only simulated return strokes with initial conditions consistent with those of subsequent strokes. In this paper, using the spectra of lightning return stroke process obtained by high-speed spectrograph in the range of 400–1000 nm, different methods are adopted to diagnose the temperature of the discharge channel. The return-stroke breakdown pulse and the dart leader are treated as electric waves guided by conducting lightning channels; such waves are launched when current is … A schematic illustration from one of the triggered lightning experiments in Florida (at the northern edge of the Kennedy Space Center in this case, not at the Univ. Res. Answer to In the return stroke of a typical lightning bolt, a current of 4.9 × 104 A exists for 45 μs. ribbon lightning. Instead of carrying 10-100 amps of current, it carries 30,000 amps—sometimes as much as 120,000. Representative models of lightning return … 1. Hamelin, A. Eybert-Berard, "Submicrosecond Characteristics of Lightning Return-Stroke Currents," IEEE Trans. The lightning channel expands rapidly outward initially as a shock wave. So how does lightning form in a cloud? The positive charges repel each other. once the stepped leader and the return stroke have connected, then electrons from the cloud can flow to the ground, and positive charges can flow from the ground to the cloud. The future is 5G and it won't kill you. Possible Impacts of Earthing Path Impedance on Lightning Return Stroke Currents. Safety1325 East West HighwaySilver Spring, MD 20910Comments? The return steamer moves very fast and produces the well known, intensely luminous lightning flash. The rest of the lightning happens either within a single cloud or from one cloud to another. This is what we see and call lightning (return stroke). The bullet won't affect the path the lightning takes. The ratio of leader to return stroke electric field change versus distance is presented as a function of stroke order for 218 first and subsequent strokes in 70 cloud-to-ground flashes which occurred near Tampa, Florida, in 1979. The validation and comparison of models in reproducing measured lightning parameters are discussed. If lightning is so powerful, why don't we tame it? On its way down, the downstroke has blasted a conductive pathway between the bottom of the cloud and the ground. But, make sure you do so safely. The faster return stroke speeds estimated by our model lend credence to the results of Liang et al. While not all negative flashes have more than one return stroke, some negative flashes have been observed with more than a dozen return strokes. If there is a flicker, the upward stroke is repeating the process. When the lightning leaders attach, the lightning zaps down in something called a discharge, and the discharge is called a return stroke. It is surrounded by a "corona envelope" or a glowing discharge that can be as wide as 10 to 20 feet (3 to 6 meters) in diameter. heat lightning . We discuss the return stroke models in two categories in accordance with the direction of the charge transfer along the channel. Subsequent Dart Leaders and Return Strokes, National Oceanic and Atmospheric Administration. The adopted propagation speeds for the return-stroke and mixed-mode pulses are in the range of the experimentally observed return stroke speeds (e.g., Idone & Orville, 1982; Rakov, 2007). What would happen if lightning struck a bullet in midair? Lightning is so impressive that when it happens it stops you in your tracks. , who predicted a current return stroke speed of 0.84c, significantly faster than the optical speed. For one thing, lightning A is a multiple return strokes CG discharge process, including four return stroke processes, which are named as R0, R1, R2 and R3, respectively, where R0 is the first return stroke and R1–R3 represent the corresponding subsequent return strokes. Part of lightning stroke may be concealed by clouds or rain or channel may be broken up. Return stroke starts from two different spots on the ground at the same time, creating two channels. Reasons for the return-stroke speed being lower than the speed of light are discussed. by first return strokes in negative cloud-to-ground lightning using a modified transmission line model. That's not the whole story, however -- a lightning flash may have only one return stroke or may have several tens of strokes using the same column of ionized air. National Weather Service For another, lightning B is a single return stroke CG discharge process. You can subscribe on iTunes, ABC Radio or your favourite podcasting app. I've also seen a problem where people use the return stroke of a lightning bolt for speed instead of the first stroke. Lightning travels at around 220,000 miles per hour when traveling downwards from a cloud, and then reaches a speed of 220,000,000 miles per hour when moving skyward on its return stroke. Frequently, after the return stroke, the thunderstorm will send down another leader, this time called a dart leader, that quickly recharges the channel and leads to another return stroke. How fast does lightning travel? This is similar to cars that have been stopped by an open drawbridge. First, and rather surprisingly, there's some actual liquid water in the shape of small droplets that are super-cooled. (Figure 1. A complete lightning discharge event can contain anywhere from a single return stroke to more than twenty, depending on the electrical structure of the storm. Learn about Subsequent Dart Leaders and Return Strokes or return to Contents page. this flow of current from the cloud to the ground is visible at the return stroke. Dileep Kumar HVE Laboratory, Dept. The return stroke is the very bright visible flash that we see as lightning, caused by the rapid discharge of electricity. Get 1:1 help now from expert Physics tutors Data were collected at the Kennedy Space Center, Florida, during the summer of 1987. Dr Karl: Can you get pregnant during a pregnancy. Robert S. Wacker, Richard E. Orville, Changes in measured lightning flash count and return stroke peak current after the 1994 U.S. National Lightning Detection Network upgrade: 2. It may seem to flicker. These two systems work by detecting radio waves (sferics) emitted by fast electric currents (strokes) in lightning channels. The electrons all come zapping down from the cloud, and it has about 30,000 amps! Once the drawbridge is opened for traffic, cars initially start moving forward toward the bridge but movement across the bridge works its way backward through the line of stopped cars. Either way, the bottom of the cloud becomes negatively charged. Dr Karl explains why, Dr Karl explains the difference between A1 and A2 milk. Lightning return-stroke models have been categorized by Rakov and Uman [1] into four classes depending on their governing equations: (a) gas dynamic models; (b) engineering models; (c) distributed circuit models; and (d) electromagnetic (or antenna-theory) models. Thanks to the strong updrafts of wind, the graupel runs into the other two types of water (the small super-cooled droplets and the small ice hail). Expert Answer 100% (8 ratings) Previous question Next question Get more help from Chegg. This downward-going lightning bolt is clearly visible—even though it's travelling at about 200 kilometres a second. Early in a return stroke, pressure in the channel is several times (maybe a few 10s of times) atmospheric pressure. For comparison, 10 amps running a domestic electrical heater will make the power cable a bit warm, while 100 amps is a bit more than your entire house can draw from the electrical grid. A flash of lightning is just 1 to 2 inches wide, but it generates a massive amount of electricity that is equal to 300 million volts, or 30,000 amps. 261 The Open Atmospheric Science Journal, 2008, 2, 261-270 1874-2823/08 2008 Bentham Open Open Access Time Domain Modelling of First Return Stroke of Lightning Udaya Kumar*, Rosy B. Raysaha* and K.P. Hence, we use the term 'discharge' to describe everything our network is capable of detecting. Most of the charge flows after this leader makes electrical contact with the ground, however. Questions? The available experimental data on return stroke speed for both negative and positive lightning are reviewed. Numerical field expressions are proposed to evaluate the electromagnetic fields due to the lightning channel with variable values of return stroke velocity. The return stroke (the current that cause the visible flash) moves upward at a speed of about 320,000,000 ft per second or about 220,000,000 miles per hour (about 1/3 the speed of light). Photoelectric data only yielded propagation speeds of 1.4, 1.6, 1.2, 1.3, 1.0 and 0.90 × 10 8 m/s for the first, second and fifth through eighth return strokes, respectively. Did you know Great Moments In Science is a podcast? 6) [27] are formed. The step leader that initiates the lightning flash propagates downward from the cloud at a rate of about 320,000 ft per second or about 220,000 miles per hour. The often assumed relationship between the return-stroke speed and peak current is shown to be generally not supported by experimental data. Lightning travels at around 220,000 miles per hour when traveling downwards from a cloud, and then reaches a speed of 220,000,000 miles per hour when moving skyward on its return stroke. Lightning appears to sway from cloud. Al Peterlin: Lightning is, generally, any and all forms of visible electrical discharge produced by thundershowers. You'd have somehow to time the shot so the bullet was in the middle of the bolt when the return stroke happened. . A return stroke explodes "up" the pathway or channel and this is what we actually see as the lightning stroke. All you see with the naked eye is the slower downward strike and a really bright flash of light from the upward return stroke. The first return stroke follows the path of initial downward-progressing stepped leader emerging from the cloud, and subsequent return strokes are usually initiated by dart leaders propagating downward along channels traversed by the preceding stroke(s). For one thing, lightning A is a multiple return strokes CG discharge process, including four return stroke processes, which are named as R0, R1, R2 and R3, respectively, where R0 is the first return stroke and R1–R3 represent the corresponding subsequent return strokes. It is known that the return stroke speed may vary along the lightning channel. Stroke : this refers to all the return strokes of a lightning flash, i.e. The only way you can "see" the upward movement of the return stroke is if you use a military-industrial-scientific-grade ultra-high-speed camera—otherwise all you see is a flash. Much of the energy in a lightning stroke is dissipated during the formation and outward growth of the shock wave. We show that all the models that we have considered can be described by two general sets of mathematical equations. Although the lightning return-stroke current, measured at the CN Tower, is simulated using the Pulse function and Heidler function, the simulation of the CN Tower lightning current derivative signal is considered using the derivative of the Pulse and Heidler functions. The air is heated almost instantaneously, making it expand explosively, producing a shock wave, which we hear as thunder. The return stroke phase of lightning involves a large transfer of charge to ground, which occurs in a front­like manner within the channel ‘carved out’ by the leader (Rakov and Uman 2003). All of this happens in a fraction of a second (Figure 3) and cannot be discerned by the human eye which is overwhelmed by the bright return stroke. If you could make the clouds and the earth invisible - allowing you to see an entire cloud-to-ground lightning strike from top to bottom, you would see a full dendritic structure very similar to a tree. A “stroke” can be a fast current within the cloud, or a “return stroke” in a channel to ground. a subsequent return stroke propagates upward from the ground to the cloud. We still don't fully understand how a bolt of lightning gets started, but we have some idea. Once the step leader makes contact with a streamer, the negative charge that has accumulated along the leader channel flows rapidly to ground. The return stroke phase of lightning involves a large transfer of charge to ground, which occurs in a front­like manner within the channel ‘carved out’ by the leader (Rakov and Uman 2003). National Oceanic and Atmospheric Administration Fast electric field changes from subsequent return strokes of natural and triggered lightning with propagation paths almost entirely over water are compared. How many forms of lightning are there? Photoelectric data only yielded propagation speeds of 1.4, 1.6, 1.2, 1.3, 1.0 and 0.90 × 108m/s for the first, second and fifth through eighth return strokes, respectively. Although the visible flash is associated with the rapid movement of charge downward, the actual flash propagates upward throughout the channel as the negative charge starts moving toward the ground (Figure 2). lightning return-stroke speed within the bottom 100 m or so of the channel. Lightning flashes into existence about 1.4 billion times each year across the whole planet. [1997], Lupo et … Frequently, after the return stroke, the thunderstorm will send down another leader, this time called a dart leader, that quickly recharges the channel and leads to another return stroke. A powerful "return stroke" releases much more energy. Lightning return stroke is a channel of fully ionized plasma, and Bremsstrahlung emission takes place in this plasma due to Coulomb field interaction of electron in its hyperbolic or parabolic orbit around the ion or atom. HKIE Transactions: Vol. While the downstroke of the lightning strike moves at about 200 kilometres a second, the upward return stroke zips along at 100,000 kilometres a second—about one third of the speed of light. Comparisons have been made of the average shape, the risetime, and the spectrum of the electric field changes. These rather perverse conditions produce three types of water. 7-13. The process begins inside a thunderstorm, where the two important ingredients are located. The whole process may take a few milliseconds (one-thousanths of a second), providing enough time to perceive motion. This stupendous amount of current is enough to create temperatures 10 times hotter than the surface of the Sun—50,000 degrees. The return stroke heats the lightning channel to an extremely high temperature in a very short time, forming the visible lightning flash and causing thunder as the lightning channel expands rapidly. This electrical tension between the bottom of the cloud and the ground can be huge—in extreme cases, it can make your hair stand on end. 1.6(c)) moves very fast up towards the cloud through the already ionized path by the leader. 1, pp. US Dept of Commerce This electrical tension between the bottom of the cloud and the ground can be huge—in extreme cases, it can make your hair stand on end. Techniques for measuring return stroke speed were discussed by I done and Orville [7]. On Earth, the lightning frequency is approximately 44 (± 5) times per second, or nearly 1.4 billion flashes per year and the average duration is 0.2 seconds made up from a number of much shorter flashes (strokes) of around 60 to 70 microseconds. The current in amps that comes from a regular plug in the wall is about 20 amps, so a lightning strike is like 1,500 plugs! All you see with the naked eye is the slower downward strike and a really bright flash … How much charge is transferred in this event? (2009). 1.6(c)) moves very fast up towards the cloud through the already ionized path by the leader. This negative charge on the bottom of the cloud induces a positive charge on the ground, a kilometre or more below. Second, as you would expect, there are small crystals of hail. NWS In the return stroke of a typical lightning bolt, a current of 4.9 × 10 4 A exists for 45 μs. Other types of lightning (see pages 399-400 in the text for more details): forked lightning; ribbon lightning; bead lightning; ball lightning; sheet lightning; heat lightning; St. Elmo's fire This is part of the reason that you get the so-called "anvil"—the large flattened area at the top of a thundercloud. There is a pause between steps of about 50 microseconds. Dr Karl Kruszelnicki explains. : the first stroke and the subsequent strokes. How wide is a lightning bolt? Each step is about 45 metres long—a tad smaller than an Olympic swimming pool. This process makes the top of the thundercloud become positively charged. The air surrounding these pauses is again ionized and the leader in this way reaches the earth (Fig.1.6(c)).Once the stepped leader has made contact with the earth it is believed that a power return stroke(Fig. These secondary return strokes often make a lightning strike seem to 'pulse' or 'flicker' on and off. All NOAA. A total of nine flashes containing 44 RS‐type ICC pulses and 24 return strokes were analyzed. These reconstructed channels are used to infer the behavior of the current in return strokes above the ground from current waveforms measured at the channel base and … Lightning is essentially a giant spark that occurs either within a cloud or between the cloud and the ground. We analyze the currents and fields associated with these fast pulses (return‐stroke type (RS‐type) initial continuous current (ICC) pulses) and compare their characteristics with those of return strokes. Theory, Journal of Geophysical Research: Atmospheres, 10.1029/1998JD200059, 104 , D2, (2159-2162), (1999). this can happen 3-4 times in quick succession. The core of a lightning bolt is a few centimeters in diameter. The first direct determination of the propagation speed of a lightning return stroke lowering positive charge to ground has been made. Multiple return strokes will cause the lightning to flicker. lightning return stroke is deliberately downplayed and the emphasis is placed on achieving agreement between the model-predicted electromagnetic fields and those observed at distances from tens of meters to hundreds of kilometers. Using fast electric-field data, we estimated the positive stroke peak current to be 21 kA. M of channel near ground and have an error estimate of 10‐15 % for each function, can... Of hail 's some actual liquid water in the shape of small that. Into the cloud and the ground, a kilometre or more below flattened area at the Space. Thunderstorm, where the two important ingredients are located cloud induces a positive charge to ground if is... From one cloud to another as half an inch ( 1.25 centimeters ) if struck., as you would expect, there are quite large blobs of soft hail with the of... 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