[TowerTalk] Weird lightning hit

[Kim Elmore]

Lightning can act very non-intuitively. I've had the pleasure of working 
with lightning scientists at the National Severe Storms Laboratory. A 
few things to ponder:

Prior to a lightning strike, the E-field near the ground gets large 
enough that everything goes into corona. Grass, trees, houses, towers, 
power lines, you name it. At that point, there are no sharp gradients to 
trigger the strike because the gradients are smoothed out. Until 
something is about 200-300 feet above the average terrain (meaning 
trees, buildings, etc., not land surface) over a broad area, it will not 
experience a higher probability of a cloud-to-ground (CG) strike.

I recall asking Dave Rust (a noted lightning physicist who became an SK 
several years ago) about how tall something needs to be to trigger 
lightning. His experience at the lightning lab in Socorro, NM, indicated 
that at *least* 200 ft was required for anything reliable. They 
triggered lightning using rockets that trailed fine wire to span the 
e-field gradient and they would sometimes fly to several hundred feet 
before triggering a strike, if they triggered one at all. Researchers 
would remain in a sealed metal enclosure intended as a Faraday cage that 
held all the recording instrumentation. Even then, he saw large arcs (up 
to a meter long) span corners of the enclosure due to cavity resonances. 
Thus, anything electronic was in the center of the enclosure (it was a 
large room) and prior to firing the rocket, everyone would huddle in the 
middle as well.

Things have to stick up in the air quite a ways to trigger lightning and 
80 feet isn't nearly enough. When everything is in corona, an 80 ft 
tower doesn't "stick out" as we night otherwise think it does.

Kim N5OP

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