Peter O. Brackett wrote:

Hi Tom:

Hmmm... Thunderclouds, lumped or distributed? It all depends upon the
application requirments... if the occurence is infrequent one may make a
quasi-static assumption and invoke DC conditions.

Then we can make an approximation and treat the lightning stroke just as a
DC conductor.

No!! A much better model is a capacitor arcing over. The current in the
strike goes from zero to Imax [100,000 amperes] in less than 1
microsecond. This is followed by a decaying current [approximate
exponential decay] that reaches 'steady state' in several 10s of
milliseconds. This is followed by an secondary exponential decay of up
to 500 milliseconds at somewhere around 500 to 600 amperes [this is
basically the sustaining or continuing channel current.

The static we hear is caused by the displacement current in the initial
discharge. The bandwidth of the static is determined by the rise and
fall times of the initial discharge characteristics.


Now... Just what is the steady state DC value for a lightning stroke?

90% of all lightning strikes in the USA have a "continuing channel
current" [long term channel current] of less than 600 amperes. It
continues for less than 1 second.


Ignoring the parasitic capacitance between strokes... we can approximate it
as a long vertical wire, without loading...

Balanced SNIPPED