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Can a lightning take the same path multiple times?

  1. Aug 27, 2011 #1
    Hi all,

    I wondered if you guys could help me with this question.
    I have been showed a picture of a lightning. It is not the complete lightning on that picture, maybe 1-2 thirds of it.
    To me it looked a little blurry, so I asked if the photographer had used a tripod to make sure the camera was completely stable for the time the shutter was open. (30 seconds)
    He said that he did use a tripod, and that the blur I was seeing was really caused by multiple flashes taking the same path.
    Looking at the pic closely you see indeed several images of a lightning on the exact same path, but moved a tiny little bit side wards, maybe the fraction of a millimetre.
    So my question is, is this possible?
    After thinking about it, it does seem to me that multiple flashes of lightning originating and ending in the same (or almost the same) spots would still take a slightly different path every time, and that it is more likely that something moved the camera a tiny little bit just when that lightning occurred.
    But would the lightning be "slow" enough to cause such an effect in that case?

    What do you all think?
     
  2. jcsd
  3. Aug 27, 2011 #2
    I read somewhere that lightning strikes are generally multiple discharges.
     
  4. Aug 27, 2011 #3
    If you read about lightning you'll find an ionized header precedes the main brilliantly visible strike...I'm sure a bit of turbulance can displace portions of that initial header a bit so each successive strike might follow a slightly different path....also portions of the path likely are re-ionized over time so that too could cause a slight displacement.
     
  5. Aug 27, 2011 #4
    During the Mount St. Augustine eruption scientists set up equipment to monitor lighting discharges that seem to always accompany volcanic eruptions. They discovered a phenomenon termed "constant lightning".

    *The really intense phase of constant lightning went on for twenty to thirty minutes.......'We saw more lightning than we'd generally see in a major thunderstorm'........'those lightning strikes lasted only 1 to 2 milliseconds and were a different kind of lightning than we had ever seen before'.

    While I realize that this might not answer the original question it does open up exciting possibilities to such an answer.


    *Kaufman, Marc: First Contact, Scientific Breakthroughs in the hunt for life beyond Earth. Simon and Schuster, 2011. pgs. 64-65.
     
  6. Aug 27, 2011 #5

    A.T.

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    Here is a nice video showing multiple strikes along the same path:
    http://www.collegehumor.com/video/6248362/super-slow-motion-lightning [Broken]

    If I understand the timer right, the entire film shows 0.3s real time. So in a strong wind the discharge channel can offset by some meters.

    But you should not see this on a picture taken from safe distance. I assume the camera was shaking. If you have lightning, you have thunder. Not yet from the one that you see on the picture, but from previous strikes.
     
    Last edited by a moderator: May 5, 2017
  7. Aug 27, 2011 #6

    davenn

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    Nice video AT thanks for the link.
    As a Stormchaser, I have often seen/videoed lightning that does multiple strikes down the same path. Some strikes are multi ones sometimes up to 8 discharges, other strikes are just a single zap

    cheers
    Dave
     
    Last edited by a moderator: May 5, 2017
  8. Aug 28, 2011 #7
    Once the electric potential builds up high enough, electricity flows towards the ground. This leaves a small path of ionized air. Once the charge reaches the ground, a larger current now forms going from the earth to the cloud due to the low resistance ionized air. The down travel is fast, but the upstroke travels at a speed of approximately 1/20 to 1/10 the speed of light. This backflow is where most of the light comes from. Once the lightning has traveled down and then back up, it repeats the process multiple times until the electric potential is no longer high enough to make lightning (about 8 or 9 round trips later). Clouds will usually take 30 seconds in between strikes to charge up.

    If you look at pictures of lightning, lightning that has reached the ground is noticeably brighter than cloud to cloud lightning or just the single flashes that don't reach the ground.

    Check out http://en.wikipedia.org/wiki/Lightning for a less garbled explanation. (I put this together from memory with Wikipedia filling in the blanks.)
     
  9. Aug 29, 2011 #8

    A.T.

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    I have a question about that backstroke/upstroke/backflow:

    What is actually flowing back up there? I would assume that the electrons are always flowing downward, from the negative cloud to the positive ground.

    Are the positive ions moving upwards and causing the flash?

    Or does "back upwards" simply mean that the dramatic increase in downward flow of electrons is initiated at the ground, and then propagates upwards?
     
  10. Aug 29, 2011 #9
    If I remember right, it's like the electrons were pushed down on the down stroke. Then, they return to about their original position releasing a lot more energy. That's just a guess on my part; I'm having trouble remembering the explanation.

    I originally heard it from MIT's OpenCourseware Electricity and Magnetism (Prof. Walter Lewin). He explains it much more clearly than I have just done. I would have hunted down the clip in question, but I have to go to class in the morning. The particular lecture in question is about Corona discharge and St. Elmo's Fire.

    Hope that helps.
     
  11. Aug 29, 2011 #10
    I believe lighting can and WILL strike in the same place twice because it will want to follow the least resistant path. Someone has probably already stated this though!
     
  12. Aug 30, 2011 #11

    A.T.

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    Thanks for the hint. I found the clip:
    http://www.youtube.com/watch?v=9501V-D-SM4#t=1524s

    To answer my own question, this is the right version:

    Or does "back upwards" simply mean that the dramatic increase in downward flow of electrons is initiated at the ground, and then propagates upwards?
     
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