I'm gonna stick with it just as I wrote it. <:-))
>
> ----- Original Message -----
> From: "Tower (K8RI)" <tower@rogerhalstead.com>
> >
> > First, Lightening is a discharge of static electricity, just like the
> spark
> > from your finger to the door knob after walking across a carpet. They
are
> > pretty much developed by the same kind of process which is friction
> removing
> > electrons from atoms.
> Not exactly.. shuffling your feet across the carpet is a somewhat
different
> charging mechanism than, say, rain drops and ice crystals being carried by
> up and down drafts.
Not really, Electrons are stripped by friction.
>The exact mechanism for thunderstorm electrification is
> the subject of a fair amount of research (made more difficult by the fact
> that thunderstorms tend to kill probes inserted into them).
True, but it's not the basics, but the actual mechanics for which we still
search.
Such as the amount of energy given off when hail stones are formed and the
amount of energy
They contribute versus the water and wind. One theory holds that only with
hil forming is there enough energy to produce thunderstorms.
>
> >
> > 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.
> (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.
>
>
> >
> > It can be, and has been shown using a Tesla coil, and Vandegraff
generator
> > that some pretty hefty sparks can be developed.
> 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.
>
>
> Add a couple Lenhide Jars
> > (sp?) and they and give you a poke you won't soon forget. It has also
been
> > shown that a single *sharp* protrusion added to the static ball on top
can
> > completely eliminate the *big* spark. A coronal discharge will develop
> > around the sharp point bleeding off the energy.
>
> Yes, indeed, having sharp corners will create corona, which will bleed off
> charge, but that's a small scale effect. On a Van deGraaff generator,
where
> you're basically charging a capacitor of a few tens of pF with a current
of
> 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. With the
sharp points the charge should start bleeding immediately while still low.
That is not to say the lightening strike could be prevented. Maybe so and
maybe not.
> (except those making ionizers<grin>) for a bunch of reasons: Where there's
> corona, there's ozone and nitrogen oxides and other reactive/corrosive
> species, which tends to degrade insulation; Corona is often a precursor to
You should see the top of my tower. I have to replace the connectors every
couple of years. The HF antenna switch looks like I'd mounted it near a
chimney. All of the connectors are badly corroded on the exterior.
Likewise, electrical tape doesn't do well. So far the longest lasting
insulation has been the UV protected heat shrink and the liquid electrical
tape.
> breakdown (by effectively reducing the total gap length)
>
> > This is the premise behind lightening rods, static balls, and static
> wicks.
> > How well it works in real life is the question.
> >
> > It should be noted that "Static wicks" are a requirement on most
aircraft
> > certified in the last 20 or 30 years.
>
> These wicks are designed to reduce P-static, not eliminate lightning
though.
> 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. Once they do that you are dead
reconing on the gauges with no nav instruments.
Essentially
> the same as putting a needle point on your Van deGraaff generator
collector.
> Charge still accumulates (from the precipitation particles (impact
> charging)) at the same rate, but it dissipates more quickly. They also
> provide a "preferred location" for the discharge to occur (i.e. the static
> wick, as opposed to your Com or Nav antennas).
>
That is true, but once the corona becomes visible the Nav and Com antennas
only hear the noise.
> >
> > OK, so we know lightening is nothing more than the release of a very
> > powerful "spark" of static electricity between two charged points
>
> Ooops.. the big problem with lightning is that it isn't a simple gap
between
> two points.
Didn't say simple gap.
> 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). OTOH I was
headed north at 5000. There was a thunderstorm over Gladwin MI (GDW). We
were well to the east by probably 15 miles.
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
pointed at the cloud, but did not get the lightening bolt. However I do
have a good photo of the area within seconds of the strike.
> thousand meters), a few tens of meter isn't going to make a lot of
> difference. And, you'd have a hard time using the "shortest distance"
It's not the shortest distance. They call it the tallest object which
doesn't mean the same thing.
> argument to explain why golfers standing in open fields get hit. The 2
> meters or so isn't going to make a lot of difference in a gap of 1000
You wouldn't think so.
> meters. Likewise, the field concentration from that golfer isn't all that
> big, in the context of the 10kV/meter kinds of fields you see before a
> strike.
> >
Again, you wouldn't think so.
Yet they tell us that if your hair starts to stand on end (been there and
done that)
curl up on the balls of your feet and make as low a target as possible and
with as small a foot print as possible. I dove in a pickup (through the
open windown) instead.
The strike hit the tower behind the truck.
The main thing is ... Lightening is unpredictable.
I'd head of it being capable of striking as much as 10 miles out fromt he
storm, but never thought I'd have a front row seat from a mile up to watch
it happen.
Roger Halstead (K8RI, EN73 & ARRL Life Member)
N833R, World's Oldest Debonair (S# CD-2)
www.rogerhalstead.com
>
>
>
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