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. : the first stroke and the subsequent strokes. Lightning is so impressive that when it happens it stops you in your tracks. 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 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. iv First, we build a modeling environment for each function, which can be described as parameter estimation system. Tom This stupendous amount of current is enough to create temperatures 10 times hotter than the surface of the Sun—50,000 degrees. 16, No. While not all negative flashes have more than one return stroke, some negative flashes have been observed with more than a dozen return strokes. 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). This is part of the reason that you get the so-called "anvil"—the large flattened area at the top of a thundercloud. The first direct determination of the propagation speed of a lightning return stroke lowering positive charge to ground has been made. Safety1325 East West HighwaySilver Spring, MD 20910Comments? lightning return-stroke speed within the bottom 100 m or so of the channel. Additionally, it is shown how a return stroke model could be utilized to study the effect of ground conductivity on the return stroke current. Data were collected at the Kennedy Space Center, Florida, during the summer of 1987. Part of lightning stroke may be concealed by clouds or rain or channel may be broken up. Above, branches extending deep into the cloud tap into areas of electrical charge. 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. Many have asked, "Why don't we capture this awesome power, and use it to power our industries and boil our kettles?". 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. Definition: Lightning stroke is the direct discharge of an electrical charge between the atmosphere and the object of earth. 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. This causes the characteristic blue-white colour of a lightning bolt. Res. US Dept of Commerce 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. Lightning flashes into existence about 1.4 billion times each year across the whole planet. . 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. 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. These rather perverse conditions produce three types of water. 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. 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. So how does lightning form in a cloud? 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. Wind blows the charged channel so position shifts between return strokes. 1, pp. This process makes the top of the thundercloud become positively charged. 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). These two systems work by detecting radio waves (sferics) emitted by fast electric currents (strokes) in lightning channels. Third, and again a bit unexpected, there are quite large blobs of soft hail with the unusual name of "graupel". On its way down, the downstroke has blasted a conductive pathway between the bottom of the cloud and the ground. A return stroke explodes "up" the pathway or channel and this is what we actually see as the lightning stroke. 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. 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. The return stroke is the very bright visible flash that we see as lightning, caused by the rapid discharge of electricity. 1.6(c)) moves very fast up towards the cloud through the already ionized path by the leader. Get 1:1 help now from expert Physics tutors Reasons for the return-stroke speed being lower than the speed of light are discussed. this flow of current from the cloud to the ground is visible at the return stroke. 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). Al Peterlin: Lightning is, generally, any and all forms of visible electrical discharge produced by thundershowers. How much charge is transferred in this event? A powerful "return stroke" releases much more energy. Theory, Journal of Geophysical Research: Atmospheres, 10.1029/1998JD200059, 104 , D2, (2159-2162), (1999). The movement of the charge starts at the point of contact and rapidly works its way upward as charge is drained from the channel Lightning is essentially a giant spark that occurs either within a cloud or between the cloud and the ground. Answer to In the return stroke of a typical lightning bolt, a current of 4.9 × 104 A exists for 45 μs. 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." All propagation speeds were evaluated over 850 m of channel near ground and have an error estimate of 10‐15%. 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. 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. , Lupo et … 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. Your information is handled in accordance with the ABC Privacy Collection Statement. 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. For a moment after the initial return stroke, the channel remains conductive and can be a favored path for subsequent downward leaders. Lett., 30(24), 2294, doi:10.1029/ 2003GL018407, 2003. Instead of carrying 10-100 amps of current, it carries 30,000 amps—sometimes as much as 120,000. 7-13. This is what we see and call lightning (return stroke). 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. But, make sure you do so safely. 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. I've also seen a problem where people use the return stroke of a lightning bolt for speed instead of the first stroke. Lightning return stroke speed is one of the main parameters in lightning modeling, so as in evaluating lightning-induced effects . Questions? Learn about Subsequent Dart Leaders and Return Strokes or return to Contents page. this can happen 3-4 times in quick succession. Using fast electric-field data, we estimated the positive stroke peak current to be 21 kA. It is important to note that Liang et al. We still don't fully understand how a bolt of lightning gets started, but we have some idea. The process begins inside a thunderstorm, where the two important ingredients are located. 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. On the transmission line model for lightning return stroke representation, Geophys. 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. a subsequent return stroke propagates upward from the ground to the cloud. (Figure 1. They move so fast that your eyes only see one flash! 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. The return steamer moves very fast and produces the well known, intensely luminous lightning flash. National Weather Service 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). Lightning is fun to watch. The return stroke is the very bright visible flash that we see as lightning, caused by the rapid discharge of electricity. Each step is about 45 metres long—a tad smaller than an Olympic swimming pool. We discuss the return stroke models in two categories in accordance with the direction of the charge transfer along the channel. 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 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. Via a complicated process, they become positively charged, while the graupel becomes negatively charged. Early in a return stroke, pressure in the channel is several times (maybe a few 10s of times) atmospheric pressure. 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. The validation and comparison of models in reproducing measured lightning parameters are discussed. 1. Multiple return strokes will cause the lightning to flicker. 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. The core of a lightning bolt is a few centimeters in diameter. Electron velocity in the partially ionized channel is non relativistic . All you see with the naked eye is the slower downward strike and a really bright flash … It happens so fast that you may not easily discern the direction of propagation. How many forms of lightning are there? Did you know Great Moments In Science is a podcast? Subsequent Dart Leaders and Return Strokes, National Oceanic and Atmospheric Administration. The stroke channel of a lightning bolt is very narrow—perhaps as little as half an inch (1.25 centimeters). 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. This stroke was the third of eight otherwise negative strokes in a triggered lightning flash initiated at the Kennedy Space Center, Florida. You can subscribe on iTunes, ABC Radio or your favourite podcasting app. 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. One flash 45 μs, intensely luminous lightning flash initiated at the Kennedy Space Center,,. 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