> Not really, Electrons are stripped by friction.
Lots of ways to put charge on something. Tribocharging is only one.
Induction or direct charge transfer (both of which are used in electrostatic
generators like Van deGraaff or Pelletrons, as well as the "Kelvin water
dropper" and it's ilk). You can also accumulate charge by merely touching
and removing (which is actually the dominant mechanism in "shuffling your
feet"). There are also things like electrets and electrophorouses.
-----------
> > > The lightening strike occurs when a low enough resistance path is
> > > established between two points be they cloud to ground or between two
> > > clouds.
> >
> > Resistance has very little to do with spark/arc breakdown in air. It's
a
>
> It has every thing to do with it. Just not in the way most people think in
> terms of resistance.
Explain further (off list, if needed).. It's E-field distribution.. granted
conductors (or semiconductors with high resistivity) will affect the field,
but for long sparks in air (which lightning certainly qualifies as), I think
that E fields are the thing to worry about.
Perhaps you are using resistance as a "term of art" to represent something
other than current/voltage?
----------
>
> > (not very well understood, in the details) ionization phenomena, with
> > cascading leaders proceeding in short jumps, with charge moving through
> the
> > leaders to the head end of the leader.
>
> How they proceeded is one thing, but the ionized air is a relatively low
> resistance compared to the sourrounding air.
Indeed, however, the leader is progressing into non-ionized air, which is
exactly the same resitivity as all the surrouding air. On the other hand,
the e-field at the leading point (head) of the leader IS greater (and, in
fact, greater than approx 30 kV/cm breakdown for air, depending on density,
etc.)
> > And, as well conventional capacitors... A Tesla coil has a v, ery
> different
> > spark propagation mechanism than lightning or a DC single shot spark
(like
> a
> > Van deGraaff generator, or, more commonly in impulse research, something
> > like a Marx generator). However, like lightning, these are all
> > characterized by extremely non uniform fields, at least at some point in
> the
> > process. (Tesla coils can make quite long sparks with relatively low
> > voltages because they are repetitive impulses and have high peak power
in
> > the impulses)
>
> True, but lightening strikes consist of a number of relatively short
pulses
> with high currents and very high, or steep rise and fall times.
Nothing like a Tesla coil. Most Tesla coils have "break rates" in the 120 Hz
or higher range. The time between strokes in a lightning flash is on the
order of 10 times slower. Furthermore, the repeat strokes in a flash follow
essentially the same path as established in the first leader, unlike in a
tesla coil where each successive spark extends a channel beyond where it had
previously extended. The rise time in a typical TC is on the order of
several microseconds, and the waveform is a classic damped sinusoid
(although often with linear, not exponential decay). Lightning has a
waveform that looks more like two superimposed exponentials (something along
the lines of exp(-at)*(1-exp(-bt))), and that's once the stroke has started.
The voltage waveform before breakdown occurs (in lightning) is much
different. In fact, there's been some work in the last few years to develop
a simulator for the "pre-breakdown" field of lightning (as opposed to the
"post breakdown" stroke current, which is adequately modeled by conventional
RLC impulse generators). In any case, a Tesla coil is very, very different
in the time history of the field before and after breakdown.
>
> >
> >
-----------------
> > microamps, a corona current of a microamp is significant. When you're
> > looking at transferring 10's of Coulombs at kiloAmps, as in lightning,
> it's
> > another story entirely. Corona is the bane of HV engineers everywhere
>
> Except the build up is not abrupt. It may take tens of seconds or even
more
> than a minute for the charge differential to build. If the build up can
be
> spread out, or partially drained it should have a positive effect.
Sure.. if the corona current is comparable to the charging current, then, by
simple algebra, the voltage (and hence, stored energy) will be limited,
since voltage is current *time/capacitance.
-------------
> > What they're really designed to do is to reduce the corona
> > inception/breakdown voltage, so that as the airplane body gets charged,
it
> > discharges in lots of little zaps as opposed to a few big ones.
>
> Those things look like little running lights when in heavy rain near a
> thunderstorm. They become a steady corona.
indicating that they are doing their job. Better to have the discharge of
the wicks than off your nav antenna?
----------------
> >
> > Ooops.. the big problem with lightning is that it isn't a simple gap
> between
> > two points.
>
> Didn't say simple gap.
Perhaps, it's better to say that looking at lightning simulators (of any
type, Marx, Tesla Coils, Van deGraaff generators, etc.) isn't particularly
representative of how lightning actually works.
>
> > At least one of the sides is a fairly large (km) scale diffuse
> > charged cloud, and the other is the earth. Sure, there are rough and
> pointy
> > spots on the earth side, but in the context of the overall scale
(several
>
> I think from what I've seen the main charges are more on the order of
rather
> localized spots a few hundred yards across (most of the time).
A spot a hundred meters across probably cannot hold enough charge to create
a lightning stroke. There is definitely "lumpiness" in the charge, however,
as evidenced by the forked/dendritic nature of the "starting end" of the
visible stroke. The whole "how the leader gets started" thing is of great
interest in the research community, since it doesn't have any good models in
laboratory equipment, where you have nice metal electrodes with high
conductivity. There is an analog in dendritic treeing in dielectrics on
breakdown, but, still, there are differences.
> He had just asked me how close we could get when the storm gave a very
> graphic answer. A lightening bolt came out of the storm at roughly our
> altitude. It came straight at us, parallel to the ground. Then it
> gracefully curved down and struck the ground about 2 miles to the west of
> us. That lightening bolt struck a good 10 miles ahead of the storm and
out
> in clear bright sunshine. Actually it was almost 10 miles of blue sky
> between the strike and the exit point from the storm. I had the camera
"Bolts from the Blue" are well known phenomena in the thunderstorm research
business, and, in fact, are responsible for a large number of fatalities in
the US. Most people are smart enough to get out of the rain, but the cell
moves through, the sun comes out, and zap, another lightning fatality.
There are some photos of such strokes in Florida. I don't recall exactly
where, but I think it was in a AMS Severe Storms Conference Proceedings a
few years back.
This points up the real problem with lightning... Measurements, such as
exist, show that there's no particular field distribution that would result
in such right angle bends, but they do. Streamer and leader propagation is
a random process in many ways.
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