glassner (01/25/83)
When in high school my physics prof described
lightning this way: A high potential difference builds
between the surface of the Earth and the storm clouds
above, which are chock-full of ions.
The air in-between ionizes, and when there's
enough ionization to permit conduction between Earth
and sky, ZAP! Lightning actually does not "fall from
the sky", but is a two-way connection between heaven
and Earth.
He claimed that this explained the usually-true
myth that "lightning doesn't strike twice in one place."
The idea was that the short-circuit removes all the
available ions in an area, so it's not likely that a
new potential difference will build up there soon.
-Not afraid to be wrong,
-Andrew Glassner
decvax!cwruecmp!glassnerrdp@teddy.UUCP (07/15/85)
During a recent flight from Boston to (yech) Allentown-Bethlehem PA, we had
the occasion to spend quite a bit of time flying around in thunderstorms.
It was quite fascinating, and I noticed two very interesting phenomenon.
First, there was a lobster walking down the aisle. (It should have kept
it's seatbelt fastened and stayed out of hot water :-)).
The second, and more mysterious was something I noticed about lightening.
The strokes (flashes, what have you) seemed not to occur at random intervals,
but with a very definite pattern. There would be a period as long 10 seconds
during which no lightning would occur, the, as soon as one flash would occur,
many more would, at very different location.
It seemed as if there was some sort of trigger mechanism at work. That is,
p[otential would build up at multiple sights, but no discharge would occur
unless A) The potential was REALLY high, and just couldn't wait, or B) the
potential was high and bolt had just occureed somewhere else.
I had offhandedly noticed this before, but from the vantage point of an
airplane (anywhere from 5000 to 25000 feet high) it was quite vivid.
Question: Is there some sort of trigger mechanism at work here? Does the
occurance of one discharge increase the likelyhood of another remotely
(greater than 1000 feet away) located discharge. If so, how does it
happen ("photoelectric" effect, increase in the ionization of the air
because of extreme electric/magnetic/RF, magic?). Am I suffering from to
little a sample here to have stumbled across a real phenomenon (possible,
but the effect was VERY apparent!)
Any suggestions?fred@mnetor.UUCP (Fred Williams) (07/18/85)
In article <936@teddy.UUCP> rdp@teddy.UUCP (Richard D. Pierce) writes: > >The strokes (flashes, what have you) seemed not to occur at random intervals, >but with a very definite pattern. There would be a period as long 10 seconds >during which no lightning would occur, the, as soon as one flash would occur, >many more would, at very different location. I seem to remember an article in some science magazine about lightning strokes being mapped. The method used was an array of microphones to record the thunder. Signal analysis, was then used to map the source of the noise, and the pattern of the lightning stroke could be clearly shown. The results, as I recollect, were that we generally only see a small portion of the discharge. A single discharge can span many miles hidden from the ground by cloud. I suspect that the many flashes you saw could really be different parts of the same stroke. I cannot of coarse be sure. I wasn't there. Cheers, Fred Williams
mikes@AMES-NAS.ARPA (07/18/85)
From: mikes@AMES-NAS.ARPA (Peter Mikes) I have no suggestion concerning mechanism of interaction but want to point out very general feature *the entrainment* of the non-linear osci- lators (described e.g. by Van Der Pol equation). They tend to synchro- nise. Example of that are fireflies, neurons etc. More on that can be found in extensive literature on circadian rythm - see Zeit-gebers. - Now of course they are acoustical waves released with discharge - the trigger can be wery week - some sea animals are said to entrain on tides.
RESS%LLL@LLL-MFE.ARPA (07/19/85)
From: David Ress <RESS@LLL.MFENET> To: physics@SRI-UNIX.ARPA In a recent bulletin, it was noted that lightning at high altitudes seemed to occur in bursts. A mechanism for such a process occurs to me. Suppose that initially we have a large build-up in potential between two clouds. The resulting electric field tends to accelerate the ambient low density of charged particles. The electrons tend to be confined to geomagnetic field lines, while the ions are less restricted. Electric fields that are oriented along the field lines would probably do the most effective acceleration (?). The accelerated particles interact collisionally with the neutrals to create more ionization, and the charged particle density rises. Finally, along some path, the line density of ionization builds up to point where the current becomes substantial, and a cascade of ion- ization leads to a major discharge. Since lightning tends to follow a jagged path, it is apparent that the discharge does not follow magnetic field lines. One explanation might be that the ions, which have relatively large gyral radii, are the majority charge carriers. Another possibility is that the plasma in the lightning discharge distorts the magnetic field to allow the discharge. Whatever the actual mechanism of the initial dis- charge, the huge energy dissipated is sure to accelerate many more charged particles. The new particles proceed to raise the background ionization still further, thus facilitating the formation of additional discharges until the potential energy of the system is exhausted. I am not an astrophysicist, although I do know a bit about plasmas. Is there an astrophysicist out there who has a better picture on lightning? -------
rdp@teddy.UUCP (07/23/85)
In article <1366@mnetor.UUCP> fred@mnetor.UUCP (Fred Williams) writes: >In article <936@teddy.UUCP> rdp@teddy.UUCP (Richard D. Pierce) writes: >> >>The strokes (flashes, what have you) seemed not to occur at random intervals, >>but with a very definite pattern. There would be a period as long 10 seconds >>during which no lightning would occur, the, as soon as one flash would occur, >>many more would, at very different location. > > I seem to remember an article in some science magazine about >lightning strokes being mapped. The method used was an array of >microphones to record the thunder. Signal analysis, was then used >to map the source of the noise, and the pattern of the lightning >stroke could be clearly shown. > The results, as I recollect, were that we generally only >see a small portion of the discharge. A single discharge can span >many miles hidden from the ground by cloud. I suspect that the >many flashes you saw could really be different parts of the same >stroke. I cannot of coarse be sure. I wasn't there. > >Cheers, Fred Williams You may be correct, except from my vantage point, I easily had a 25-30 mile view of things, and could see similar patterns in remote locations. I will post a summary of conclusions in a week or so, and then we can all nominate each other for the Nobel prize in physics.