[TowerTalk] Re: static cat

[Didier Juges <didier@cox.net>]

The problem is that the ground is not charged, the clouds are charged. 
Think of the earth and the cloud as both plates of a capacitor, except that 
the bottom plate is a few 10 of thousands of miles long and conductive, and 
the top plate (the cloud) is a few thousand feet wide, and basically a 
charged insulator (each water droplet is charged, but isolated from its 
neighbor. The charge on the earth side is for all practical purposes 
infinite. You cannot drain it to anywhere because it always returns to earth.

When charges escape the porcupine, they do not make it to the cloud. They 
just dissipate in the air and return to ground, so they do not contribute 
to reducing the charge in the cloud. I'll agree that they may locally 
reduce the field in the air somewhat (as seen from a distance of a few 
feet). The argument is whether that reduction is sufficient to reduce the 
probability of a lightning coming from hundred or thousands of feet higher up.

Think of it another way. The earth is conductive. At least until lightning 
strikes causing great amounts of currents, before that point little current 
flows, so the potential along the earth is not affected very much by a few 
charges flowing out of a porcupine because the earth is conductive and 
charges are replaced as soon as they escape. Charges may be flowing out and 
into the air, but the earth's potential is the same, and the potential 
difference between earth and the cloud is what causes the lighting to go.

The other side of the argument is whether it is actually a good thing to 
eliminate smaller strikes, as they act as bleeders and may prevent the 
larger strikes.

I am not sure I want a lightning protection device that would reduce the 
number of smaller strikes at the expense of greater probability of getting 
the big one.

There is a lot of anecdotic evidence that these types of devices work, but 
no serious, objective, peer reviewed studies to support the same.

The bottom line, as long as you are happy with it, and you do not cause 
other problems doing this, why not do it? Just be aware that it may or may 
not work, and it may even increase the probability of getting a serious hit.

73,
Didier KO4BB

At 10:20 AM 3/21/2004, you wrote:
> I think that's the key.  Their web page is misleading, but, in my own
> belief, not entirely wrong.  Yes, there will be direct strikes to the
> tower, even the whiskers.  But before the differential reaches the point
> of discharge, I think the whiskers are trying hard to discharge it
> slowly, thus preventing some of the smaller strikes.


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