Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Why does Lightning Zig-Zag

  1. Aug 9, 2007 #1
    Why doesn't the bolt make a smooth arc shape? Why doesn't it just follow a straight path to the ground?
  2. jcsd
  3. Aug 9, 2007 #2


    User Avatar
    Gold Member

  4. Aug 9, 2007 #3
    path of least resistance, electricity
  5. Aug 9, 2007 #4
    "path of least resistance, electricity"

    pretty much, in vacuums electrons go in straight lines.. in the case of lightning they gotta push through the molecules in the atmosphere... maybe they zig zag between stray ions and polar molecules =)
  6. Aug 9, 2007 #5
    Off hand, it's where the charges are located. I think too thatjust how it forms probably depends upon ionization trails of cosmic rays too, permitting some of the first conduction. I don't think it has anything to do with general relativity but rather EM theory.
  7. Aug 10, 2007 #6
    Why is this path a zig-zag path?
    Yeah, but a sinking ship doesn't zig-zag.
  8. Aug 10, 2007 #7
    Do you think it is like a "connect the dots" type thing?
  9. Aug 10, 2007 #8


    User Avatar
    Gold Member

    Electrical charges can jump from one potential to another more easily when there is a path established, which is why I think the page I linked might have some real insights regarding ionizing radiation. One reason I think this is that in our old house, we had an overhead kitchen light on an old rheostat-type dimmer. On dry winter days, if the light was dimmed and I got out of an upholstered chair, walked over, and reached toward the dimmer knob, I'd get a fat blue spark of static electricity to one of the grounded screws holding the face-plate, and the kitchen light would momentarily get very bright. There wasn't enough static electricity on me to brighten those bulbs, BUT the voltage in that static electricity was high enough to jump a much higher potential than the 120V feeding the fixture could, and the 120V (with a lot of amperage on tap) jumped that gap along with the high-voltage spark for as long as the spark lasted.
  10. Aug 10, 2007 #9
    Do you think it is like a "connect the dots" type thing?

    I'm not sure what you're asking but basically, air is an insulator that doesn't conduct electricity normally. The amount, size and shape of of electric charges determine how strong an associated electric field is. If the electric field is strong enough, it will conduct. Big balls like van de graaf generators have offer very low electric fields per the charge involved. Small sharp objects like the tip of a tesla coil or a lightning rod have very high electric field strength at the tip and so discharge before all that much charge is present.

    In clouds, charges build up all over the place and electric fields exist all over as well. Sooner or later one or more of these electric fields reach critical strength, or perhaps a cosmic ray ionizes a path through the middle of it where things start to conduct and bam, lightning and thunder.

    While moving electrons are subject to change of direction from magnetic fields, the energy is coming from differences in statics voltage levels or electric fields (same sorta thing).

    A lightning bolt can go from a cloud out and down such that something miles away from the cloud might be struck.

    Additionally, there are upper phenomenon called sprites and jets that were officially discovered sometime after I was in school. They indicate a relationship or tie in with the upper atmosphere far above the clouds - perhaps a tie in to the cosmic ray notion I've mentioned.

    Ultimately, the lightning bolt is going to take the direction and path determined by the electromagnetic forces involved which are far stronger than gravity and other forces and those will substantially depend upon the location of the charges in the clouds and on the ground.
  11. Aug 10, 2007 #10

    Ivan Seeking

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    I think part of this results from the step-wise nature of lightning. Each discharge is a series of steps in which the current travels a short distance and then pauses. Each pause is where you see a change in direction. Meanwhile the local potential to ground is constantly changing, so the final target is constantly changing. As the discharge approaches the earth, many potential targets might be seen, but only one or a few will ionize the local air enough to provide the final path to ground. Failed step-leaders have even been filmed where a small discharge is seen coming from objects that were failed targets - that apparently couldn't ionize the local air quickly enough to win the strike. So even up to the final moment, a battle for the strike is underway between competing targets.

    Note also that this merely establishes the path. The "return stroke" occurs once the path is completely established; only then does a large current [hole] flow occur from the ground to the cloud; or on rare occasion, from cloud to ground.

    While the lighting is approaching the ground, charges in the earth are rushing towards the discharge, so I would think that local variations in ground resistivity might in part govern the path followed by the lightning. I also know that it is difficult to make lightning strike a particular spot. There has been a great deal of work done in trying to make the best lightning rod... some people even tried using radioactive materials that would create a cloud of ionized particles above the rod! But even with the best rods, lightning still might strike right next to the rod, damage the building, and miss the rod altogether. So I think the complexities of targeting [local ionization] and ground charge movemement could be parts of your answer.
    Last edited: Aug 10, 2007
  12. Aug 10, 2007 #11
    Actually, the true purpose of the lightning rod is really to relieve a charge buildup so lightning doesn't strike. That is the true purpose after it was figured out that it doesn't work very well to catch and 'guide' a discharge. Lightning doesn't like to change directions and sometimes tries to go straight when the conductor turns a corner.

    As for the cloud - it's all about lots of potential voltage differences in the cloud as well as on the ground. And, it's best to remember that ben franklin was virtually unique in the arena of lightning research. He survived his research project.
  13. Aug 10, 2007 #12

    Ivan Seeking

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Lightning rods are designed to transmit the current from a strike to ground, not to relieve a charge build-up.

    What you are talking about are lightning dissapators that are intended to reduce the cloud-to-structure potential by slowly leaking charge to the atmosphere; in principle reducing the level of accumulated charge resulting from the cloud-to-ground potential. These have been controversial but they seem to be gaining favor for very tall towers.

    Also, yes, the cloud to cloud potential can be a significant factor as well. I would imagine that this [repulsion] might even dominate as the step leader leaves the cloud, and earth variables influence the path as the strike nears the earth.

    As a matter of detail: The step leader [low current, usually negative charge] moves away from the cloud in steps about 50 meters long, with about a 50 microsecond pause after each step.
    Last edited: Aug 11, 2007
  14. Aug 11, 2007 #13
    I've read that the electrical fields inside clouds are, by themselves, not enough to result in lightning. I think this is the reason that some suspect that cosmic rays are involved. If this is the case, then maybe the electric field isn't enough for the bolt to travel through the air either.

    I imagine that the Earth's atmosphere is pock-marked by cosmic rays. As cbacba said, these cosmic rays form ion trails. I suspect that these ion trails likely have directional bias towards the Earth's surface because the Earth itself probably has some kind of shadowing effect.

    My thought was that lightning might be connecting the dots between different ion trails. The reason it so often goes from cloud to ground is because these trails happen to be biased in that particular direction. I'm just speculating though
    Last edited: Aug 11, 2007
  15. Aug 11, 2007 #14
    If you ever saw the output of a detector as large or larger than a person, you'd wonder why you're still alive with all that radiation around. Most people see at best some little handheld geiger counter device with a moderately insensitive detector half an inch in size. A single potent cosmic ray particle coming in to the atmosphere can generate a shower with millions of ionizing secondary particles cascading down thru the atmosphere. For the most part, they're headed down for whatever reasons might be involved such as the earth shadowing the 'up' direction. They definitely don't come straight down for the most part.

    I'm pretty sure you're correct on the trails following ion trails. The reason so much cloud to ground lightning is because there's a difference in potentials. Wind blowing dust is not all that different from rubbing an amber rod with a cat fur rag - or whatever gets used these days for electrostatic education in school.

    At best, the cosmic ray shower is going to open the paths up for conduction between charge concentrations. It's a trigger mechanism. Once the path is open then multiple strikes are possible down the same path if the timing is fast enough to utilize the trails.

    Otherwise, there's always some natural background radiation in the atmosphere.

    One thing compelling to me about the cosmic ray idea is that there are activities associated with lightning that happen above the clouds - sprites and jets - out into the edge of space.

    Please note too I've not studied anything of lightning in the modern era - after the discovery of sprites and jets so I'm likely speculating about things that may well be known (or known not to be).
  16. May 9, 2009 #15
    i asked my physics teacher this question and he said it had to do with the lighting being a plasma and stripping the electrons off atoms and molecules and then it being up to electromagnetic fields as to in which direction it goes.

    now i comment now because he was irriated that i asked the question whilst the topic we're studing is vectors and scalars (which i've already learned in engineering studies), so i was sceptical to his answer and googled it and this is what came up and i thaught well while im here i can ask some other questions.

    and those other questions are why does lightning branch out as it does, if my physics teacher is right why doesent it just become a single sort of ray or beam? and if my belief is right and lighting spilts oxygen molecules to create O3 then why wouldnt we artifically create lighting to make more O3 and fix up our ozone layer? after all we can artifically create lightning cant we?

    now i've probably gone outside the topic but it is my first post.
  17. May 16, 2009 #16
    Welcome to the forum! If I'm not mistaken, the path taken by lightning can be described using vectors.
  18. Sep 24, 2009 #17


    User Avatar
    Gold Member

    Zig-Zag Lightning paths.

    Scientists who study lightning refer to these zig-zag paths as “tortuosity”. No one knows yet how to explain what causes it. One of the most respected scientists in the field is Martin A. Uman, and here is a chapter from one of his books where he addresses tortuosity:


    Here is a biography and research description of Vincent P. Idone who is studying the subject, plus lots more references:

    http://www.atmos.albany.edu/facstaff/idone.html [Broken]

    Two detailed technical reports are:
    R.D. Hill, "Analysis of Irregular Paths of Lightning Channels," J. Geophysical Research, Vol. 73, No. 6, March 1968, pp. 1897-1906.
    D.M. LeVine and B. Gilson, Tortuosity of Lightning Return Stroke Channels, Tech. Report TM 86104, Goddard Space Flight Center, Nat'l Aeronautics and Space Administration (NASA), Greenbelt, Md., May 1984.
    There probably is more recent work, so you may want to search more.
    Last edited by a moderator: May 4, 2017
  19. Sep 24, 2009 #18
    Cosmic rays leave a track of ionized air over a length of several hundred meters. These tracks are the least resitive path for a lightning bolt. These tracks of free electrons and ions recombine quickly, but are replaced by other cosmic ray tracks. Based on the LBL Table of Atomic and Nuclear Properties of Materials:
    The radiation length and the nuclear collision length of high energy charged particles in air are 37 and 90 grams per cm-square. Using an air density of 1.2 Kg per cubic meter, the radiation length and nuclear cascade development lengths in air are 31 and 75 meters respectively. These are the effective lengths of electromagnetic and nuclear cascade development in air. It is very likely that lightning follows these ionization tracks.
  20. Sep 24, 2009 #19
  21. Oct 11, 2009 #20

    Vanadium 50

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor
    2017 Award

    If you're interested in lighting, I highly recommend Martin Uman's book, entitled simply Lightning.

    The role of cosmic rays on lightning is unclear. Gurevich and others have suggested that cosmic ray ionization acts as a trigger, and the zigzagging is due to the bolt following ionization trails. He co-wrote a very interesting article in Physics Today about this: "Runaway Breakdown and the Mysteries of Lightning", Physics Today, May 2005.

    One puzzling bit of evidence is that there is a correlation between x-rays and lightning. The question is whether the lightning causes the x-rays (meaning there is a much more energetic component to it than thought) or whether the x-rays cause the lightning, as in a cosmic ray air shower.
  22. Oct 11, 2009 #21


    User Avatar

    Staff: Mentor

    First of all - air is not homogenous. Especially during storms it is highly turbulent, with density and humidity gradients, and it is not continuous as it is full of droplets of water. It would be rather surprising if the lightning would be straight in such circumstances.
  23. Oct 12, 2009 #22


    User Avatar
    Gold Member

    Vanadium 50,
    Thank you for recommending Martin Uman’s book “Lightning”. My copy is dog-eared from years of use. And thank you for the reference to Gurevich’s paper in Physics
    Today, May, 2005 “Runaway Breakdown and the Mysteries of Lightning”. It is very interesting, but unfortunately in it I found no mention whatsoever of zig-zag, or tortuous, lightning paths. The original question in the OP remains unanswered.
  24. Jan 12, 2010 #23
    And that is because when a ship sinks, the water around it creates a vaccum. :)
  25. Jan 13, 2010 #24


    User Avatar

    Staff: Mentor

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook