Precisely that, Jerry...
They've collected gigabytes of data from field mills all over Cape Canaveral,
and I'll bet they really don't have a real handle on what might make a strike
one place rather than the other. Sure they can predict that they'll get X
number of hits within Y area over a given time span, but as to what might
explain the phenomenon you mention..
There are folks seriously looking at storm electrification and the fine scale
behavior of lightning storms, but, it's hard to get lots of data. You CAN say
that if you're the highest grounded thing for miles around, you're probably
more likely to get hit, IF there is a strike, but as to whether the structure
might affect the rate of lightning....
There are people looking to trigger lightning artificially to protect high
value items (rockets sitting on pads?) using things like lasers to ionize the
air, but I don't know that it works all that well. It certainly doesn't work
well enough for them to discard all the conventional lightning protection (i.e.
strike damage protection) surrounding the gantry and launch facility. If
you've got a $100M box or a billion dollar shuttle sitting there, you'd have to
have a LOT of faith in your lightning prevention widget to justify getting rid
of the existing mass and hassle of EMP/Lightning protection stuff.
----- Original Message -----
From: Jerry Keller
To: Jim Lux
Sent: Tuesday, July 06, 2004 3:19 PM
Subject: Re: [TowerTalk] Lighting
And so we are left to attempt to define the undefinable in terms of
explaining its behavior. I refer again to the many instances described by guys
in the midwest, that T-storms with lots of lightning seem to stop striking as
they pass over their well-grounded tower farms, and resume striking after they
have passed. I have seen some of this myself at a distance, and the only thing
that makes any sense is that the ground under the towers is sometimes less
attractive for a strike than the ground elsewhere.
I love a mystery!! :-) 73, Jerry K3BZ
----- Original Message -----
From: Jim Lux
To: Tom Rauch ; Wilson Lui ; 'David Robbins K1TTT' ;
towertalk@contesting.com
Sent: Tuesday, July 06, 2004 5:56 PM
Subject: Re: [TowerTalk] Lighting
----- Original Message -----
From: "Tom Rauch" <w8ji@contesting.com>
To: "Wilson Lui" <wilsonlui@atitec.com>; "'David Robbins K1TTT'"
<k1ttt@arrl.net>; <towertalk@contesting.com>
Sent: Tuesday, July 06, 2004 2:07 PM
Subject: Re: [TowerTalk] Lighting
> Thanks Dave and Wilson.
>
> > Grounding does not prevent strikes. What a proper
> grounding system does do
> > is allow for any lightning strike that does happen is
> condected safely into
> > the surrounding soil and not arc through any
> equipment/structure trying to
> > find a lower resistance path to earth.
>
> That's my opinion also, based only on the physics involved.
>
> I notice a large group of people actually think lighting
> does not hit grounded structures because grounding causes
> the charges to bleed off or dissipate.
>
> I'm curious where that idea actually came from. Does anyone
> know?
>
It might go back as far as Ben Franklin, inventor of the lightning rod.
There is much "lore" (no better word for it.. anecdotal, not based on any
sound theoretical basis, etc.) about one kind of air terminal or another.
The problem is it's really, really, really hard to do objective tests.
There were some researchers at Erico (in Australia) who designed a HV power
supply that can recreate the E field time history before the strike to do
the testing, but I think they ran out of funding or were transferred or
found other jobs before they got any substantive results. The usual HV
testing deals with the "after the strike" currents (e.g. the classic 2
microsecond rise time (10%-90%) and 50 microsecond fall (to 50%) double
exponential used for lightning impulses) or for switching surges (much
slower rise and fall times).
As it happens, there's not much commerical market in validated lightning
prevention.. Nobody has anything that's 100% guaranteed, so you'd have to
have a afterstrike damage protection scheme anyway, and once you have that,
you don't care as much about whether you do or don't get hit. There's
plenty of market for one sort of air terminal or another, but, it appears
(to me) that the selection would be based more on speculation than any hard
science.
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
questions and ask for Sherman, W2FLA.
_______________________________________________
TowerTalk mailing list
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http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
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