[TowerTalk] Static Discharge Porcupines - great for....

[Jim Lux]

On 8/8/15 6:11 PM, Roger (K8RI) on TT wrote:

>
> I'm glad Kim posted that information, but I wish the scientific
> community would go back to averages rather than median.  The average is
> much more meaningful than knowing the number that lies half way between
> the highest and lowest figure measured, at least they are for me. Median
> is an interesting number, but average seems to be much more informative
> and typically what is used for design.  With a number of samples large
> enough to be statistically valid a single, significant outlier, be it
> high or low can substantially skew the median, but have little effect on
> the average.


Actually, the median is the one you want: half the strokes are higher, 
half the strokes are lower.   it is not skewed as much by a outlier. 
The mean (arithmetic sum divided by the number of entries) would be 
skewed by a single very large number.

In practice, what you'd really want is something like the 95th or 99th 
percentile. And that's something that's in the standard scientific 
literature.  I think pretty much any of Uman's books has a figure in it 
of stroke current distribution.

http://www.iclp-centre.org/pdf/Invited-Lecture-3.pdf

has a lot of interesting charts..
On page 10, it shows that 50% of the first strokes are around 35 kA or 
less, and 90% are <100kA peak.

http://surgelogic.com/documents/technotes/Lightning_Stroke_Tech_Note_1300DB1101.pdf
says 95% of positive strokes <30kA, 98%<60kA
for negative strokes, 82%<30kZ, 98%<60kA

>
> The so called "super strikes", or Positive lightening, which is
> associated with sprites can move the median, but happen so seldom, they
> have little effect on the average and when it come to lightening, do we
> design for the median, average, maximum, or the best we can afford?


Design for what you can afford to lose. I suspect that designing for the 
99th percentile is inappropriate for hams..