Using fast electric-field data, we estimated the positive stroke peak current to be 21 kA. One-and-a-half billion lightning bolts sounds like a lot, but only about one quarter of them get to the ground. Second, as you would expect, there are small crystals of hail. 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. Scientists have learned some facts about lightning from pictures. It may seem to flicker. 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. First, there's air moving rapidly upwards, and second, there are freezing temperatures (ranging between 15 and 25 degrees below zero). US Dept of Commerce Al Peterlin: Lightning is, generally, any and all forms of visible electrical discharge produced by thundershowers. For another, lightning B is a single return stroke CG discharge process. Lightning is fun to watch. The process begins inside a thunderstorm, where the two important ingredients are located. Did you know Great Moments In Science is a podcast? 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. Possible Impacts of Earthing Path Impedance on Lightning Return Stroke Currents. 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. A “stroke” can be a fast current within the cloud, or a “return stroke” in a channel to ground. The first direct determination of the propagation speed of a lightning return stroke lowering positive charge to ground has been made. 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. On its way down, the downstroke has blasted a conductive pathway between the bottom of the cloud and the ground. If there is a flicker, the upward stroke is repeating the process. 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. 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]. Hence, we use the term 'discharge' to describe everything our network is capable of detecting. by first return strokes in negative cloud-to-ground lightning using a modified transmission line model. For another, lightning B is a single return stroke CG discharge process. 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. Safety1325 East West HighwaySilver Spring, MD 20910Comments? Either way, the bottom of the cloud becomes negatively charged. 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. Lightning is so impressive that when it happens it stops you in your tracks. A return stroke explodes "up" the pathway or channel and this is what we actually see as the lightning stroke. So how does lightning form in a cloud? 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. 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. 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. 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 … All NOAA. This downward-going lightning bolt is clearly visible—even though it's travelling at about 200 kilometres a second. only simulated return strokes with initial conditions consistent with those of subsequent strokes. Concepts of lightning return stroke models Abstract: Return stroke models have been reviewed according to the assumptions they make and their underlying concepts. The faster return stroke speeds estimated by our model lend credence to the results of Liang et al. 7-13. This negative charge on the bottom of the cloud induces a positive charge on the ground, a kilometre or more below. NWS Questions? 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). a subsequent return stroke propagates upward from the ground to the cloud. The numerous pulsing return strokes occur in rapid succession, making the lightning bolt appear to flicker on and off. 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 wide is a lightning bolt? 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 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. The rest of the lightning happens either within a single cloud or from one cloud to another. Lightning strikes Sydney Tower during a storm. It happens so fast that you may not easily discern the direction of propagation. 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. 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 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 … Techniques for measuring return stroke speed were discussed by I done and Orville [7]. of Electrical Engineering, Indian Institute of … Please Contact Us. All propagation speeds were evaluated over 850 m of channel near ground and have an error estimate of 10‐15%. 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. How fast does lightning travel? Lett., 30(24), 2294, doi:10.1029/ 2003GL018407, 2003. Via a complicated process, they become positively charged, while the graupel becomes negatively charged. Expert Answer 100% (8 ratings) Previous question Next question Get more help from Chegg. this flow of current from the cloud to the ground is visible at the return stroke. Additionally, it is shown how a return stroke model could be utilized to study the effect of ground conductivity on the return stroke current. 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. The return stroke is the very bright visible flash that we see as lightning, caused by the rapid discharge of electricity. How many forms of lightning are there? Dileep Kumar HVE Laboratory, Dept. Stroke : this refers to all the return strokes of a lightning flash, i.e. this can happen 3-4 times in quick succession. 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). 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 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 return-stroke speed within the bottom 100 m or so of the channel. 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. They move so fast that your eyes only see one flash! On the transmission line model for lightning return stroke representation, Geophys. Numerical field expressions are proposed to evaluate the electromagnetic fields due to the lightning channel with variable values of return stroke velocity. 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. 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. The lightning channel expands rapidly outward initially as a shock wave. Wind blows the charged channel so position shifts between return strokes. CG return strokes usually have larger currents that make stronger signals that are easier to … This causes the characteristic blue-white colour of a lightning bolt. 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. 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. National Weather Service 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 validation and comparison of models in reproducing measured lightning parameters are discussed. The available experimental data on return stroke speed for both negative and positive lightning are reviewed. 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. Eventually, over about a 20,000th of a second, a lightning strike stutters its way towards the ground in a series of steps. The whole process may take a few milliseconds (one-thousanths of a second), providing enough time to perceive motion. 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. Your information is handled in accordance with the ABC Privacy Collection Statement. The stroke channel of a lightning bolt is very narrow—perhaps as little as half an inch (1.25 centimeters). 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. 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. How much charge is transferred in this event? iv First, we build a modeling environment for each function, which can be described as parameter estimation system. This process makes the top of the thundercloud become positively charged. 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. Return stroke starts from two different spots on the ground at the same time, creating two channels. 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