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 | +-------------------------------------------------------+--------+