Re: 20 joules at 100 bps vs 4 joules at 500 bps

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>

At 12:17 PM 8/4/2005, you wrote:
> Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>
>
> Hi Jim,
>
> Is there something here that is uniquely different??  Are we talking 
> about the field strength at the point of origin for the lightning or 
> the average field strength??
>
> Gerry R.
>
> > Original poster: Jim Lux <jimlux@xxxxxxxxxxxxx>
> >
> > At 02:35 PM 8/3/2005, you wrote:
> > > Original poster: "Denicolai, Marco" <Marco.Denicolai@xxxxxxxxxxx>
> > >
> > > Hello Jim, all,
> > >
> > > Based on my readings there are 3 different situations for breakdown:
> > >
> > > - small gaps (some cm), Efield required 30 kV/cm, breakdown with 
> > > avalanche (Townsend).
> > > - medium gaps (< 1 m), Efield required 5 kV/m, breakdown with 
> > > stable streamers and final jump.
> > > - large gaps (> 1 m), Efield required only 1 kV/m, breakdown with 
> > > leader-streamer phases and final jump.
> > >
> > > These phenomena are very well documented, although usually with 
> > > different names and in not such a clear manner. So, for a 2 m 
> > > breakdown you need a 30 kV/m on the toroid surface, then at least 
> > > some 5 kV/m within 1 m from it and the rest of the travel will 
> > > succeed if 1 kV/m can be ensured.
> >
> > Indeed... for instance, lightning typically starts in a field of a few kV/m.
> >
> > Bazelyan and Raizer have a fair amount of description of breakdown 
> > conditions in non-uniform fields at high voltages, although not 
> > such a nice table as you have created.

That's observed field at the ground before a lightning strike 
(typical numbers are in the few kV/meter, but sometimes as high as 
20kV/m).  Calculations of the overall field (i.e. the voltage 
difference between cloud and ground divided by the height of the 
cloud) can actually give lower numbers. (B&R say hundreds of V/m)

Obviously, it's tough to measure this sort of thing accurately 
(especially when there are spatial variations), so there's a fair 
amount of uncertainty.

What's important is that it's nowhere near 3MV/meter, although, the 
field "somewhere" must be greater than 3MV/meter or the lightning 
wouldn't start in the first place.