franka@mmintl.UUCP (Frank Adams) (07/30/85)
This thought occurred to me the other day, regarding bursts of lightning. Could the surge of current from a lightning bolt set up trickle currents nearby, which would provide a path for other lightning bolts? I haven't tried to compute the size of the currents which would be induced by a lightning bolt, but this seems intuitively plausible to me.
pmk@prometheus.UUCP (Paul M Koloc) (08/01/85)
> Once one lightining strike has ionized the air it leaves a path of lesser > resistance than existed before. That alone should make successive strikes > more probable until the available potential has diminished. Then air > turbulence eliminates the ionized path and the max potential must rebuild. > > This does not explain why paths OTHER than the first one appear to be part > of the cluster of strikes that follow the first one, a phenomena I have > observed myself (from the ground). My suggestion is that there is > leakage current moving through the air that preceeds the strike and that > they are ALL about ready to produce stike paths. Which one goes first is > therefore random and the burst is NOT "caused by" the first one. > > Rick Merrill 617-493-3751 Cloud to ground lightning generates a vaccuum channel which persists for a couple of milliseconds. "M" strokes can light up the vacuum channel sort of like a florescent tube without the phosphor. Consequently such strokes are only seen using image intensifier fast optics. It is more likely that multiple strokes which can be seen by rapidly moving ones eye back and forth so as to spacially separate the strokes on the retina, probably track along the same breakdown path (stationary with respect to the air mass), because of the copius generation of ozone and nitrous oxides which are which are quit unstable. Also, oxygen and these compounds are electrophilic and will attach electrons to form negative ions. These ions give up free electrons in a relatively weak field as far as lightning potentials go. The triggering of ancillary cloud to cloud lightning probably occurs because once a cloud to ground stroke occurs the charge of the adjacent clouds redistributes and this produces a series of cloud to cloud lightning. The potential to generate a discharge is less in clouds with heavy rain so that such charge redistribution can also signal the potential build up it takes to generate a new cloud to ground stroke. So that cloud to cloud strokes can preceed a cloud to ground stroke. Dry air strokes often generate the biggest wallop. They usually come from the leading edge of thunderheads along a fast squall line. A boys camera (wide angle lens looks straight up) took a picture out west (krider at arizona) that showed a stroke which had feed branches spreading out radially for forty miles. And there are "bright" lightning strokes off the coast of Japan that have triggered nuclear bomb monitors in satellites. Suggested energies were well over 10^11 joules. One more interesting thing. Charge on tiny rain drops tends to prevent their merging. So usually two minutes after a nearby heavy stroke (rain drop fall time), the rain will start or increase significantly. That's more reliable at the beginning five or ten minutes of a rain storm. - - NOTE: MAIL PATH MAY DIFFER FROM HEADER - - +-------------------------------------------------------+--------+ | Paul M. Koloc, President: (301) 445-1075 | FUSION | | Prometheus II Ltd., College Park, MD 20740-0222 | this | | pmk@prometheus.UUCP; ..seismo!prometheus!pmk.UUCP | decade | +-------------------------------------------------------+--------+
pmk@prometheus.UUCP (Paul M Koloc) (08/15/85)
Mark Brader observes: > I happened to videotape a TV news show a couple of weeks ago > that included a view of a lightning strike (in Wyoming). > It was interesting to play it back in slow motion. > In both of those frames there was a bright aura splaying out from the bolt; It sure was!. Thanks for putting me on to it because I had the same news ariticle on video tape. So I did the same examination and it turns out that in my recording the "framing" didn't "split" the stroke. What I saw as the step leader "aura" which was very wide at the top, and not so wide at the bottom. I discussed this in a previous reply to this same topic. However, reference to a "charge cylinder" was made and what is apparent is that the charge cylinder varies quite a bit in width as a function of height. In fact, it's much wider at the top than previously expected, but, it makes sense just because of the density variation and longer time for radial expansion. The aura was created by the "charging" radially outward flow of electrons from the tip of the step leader as it descends. The "first frame" showed the integrated picture of the step leader formation, and the next one the return stroke. The second thing that was obvious and very surprising. It was an afterglow of the return stroke channel, and that afterglow remained in the air for better than a second. It wasn't an "afterimage" created by the bright return stroke image. Brader observes: > The frame after the washed-out frame had no lightning in it, though there > was a powerful afterimage (artifact of the TV camera, I assume) that faded > in about 1.5 seconds. Nope!, it was "really there". How do I know this? Glad you asked. The image "moved with the big wind" and it moved less near the ground due to the "strong wind shear". The camera was not panning at the time and the other ground objects were still. It was quite amazing how much neater it is to have a TV camera image recorded on mag tape so that it can be played back a frame at a time to see the much better time resolution than our eye is capable of achieving. All things considered it was a nice piece of work Mark Brader! - - NOTE: MAIL PATH MAY DIFFER FROM HEADER - - +-------------------------------------------------------+--------+ | Paul M. Koloc, President: (301) 445-1075 | FUSION | | Prometheus II Ltd., College Park, MD 20740-0222 | this | | pmk@prometheus.UUCP; ..seismo!prometheus!pmk.UUCP | decade | +-------------------------------------------------------+--------+