LIGHTNING STRIKE PROBABILITY
 

pair of lox, weren't you the guy who claimed expertise in all things because
you have an EE degree in physics?

Yup, that was you.

(Parallax)
Date: 7/10/2004 12:16 PM Eastern Standard Time
Message-id:

"rnh17" wrote in message
...
How do you define "effective" area?
Your equation assumes that any lightning within the effective area of your
boat will strike your boat. If that were the case I'd be very afraid.

"Parallax" wrote in message
om...
Out of curiosity, I did a quick back of the envelope estimate of the
probability of a lone sailboat getting hit by lightning in a
thunderstorm.

...


As I said, effective area is defined as pi*9*(mast height squared).
This is comes from the distance over which a conductor over a flat
conducting plane (3* mast height) has minimal effect on the electric
field distribution(you know, the area of a circle being pies are
squared.

Telephone poles have conductors attached to them and normally have a
ground wire. Trees on the top of a tall hill all alone would not last
long if active thunderstorms passed over them often enough. Around
here, tall pines get hit and die while many other trees survive
strikes. Look at pines with vertical slashes on them running waaaay
up the tree, this is often caused by lightning strikes.

If you do not believe my 1 in 20 chance, consider the number of
golfers who get hit each year here in FL playing during thunderstorms.
Furthermore, find something wrong with my reasoning. Since the math
is correct, the only possibility is that the cloud to ground strike
rate is too high but I watched such strikes during a storm to get this
rate.

I believe my analysis is correct, and until I did this simple
calculation based on area, my experience with electrostatics had
caused me to think the probability should be MUCH higher with this set
of assumptions.

LIGHTNING STRIKE PROBABILITY
 

"rnh17" wrote in message ...
How do you define "effective" area?
Your equation assumes that any lightning within the effective area of your
boat will strike your boat. If that were the case I'd be very afraid.

"Parallax" wrote in message
om...
Out of curiosity, I did a quick back of the envelope estimate of the
probability of a lone sailboat getting hit by lightning in a
thunderstorm.

...

I found a web site that gave a strike rate of about .5 strikes/km^2/yr
but they did not say where they measured this. However, this means
that a lone sailboat with a mast 17 m tall would have a .35% chance
each yr of getting struck. This is an ideal situation though and may
not address the situation of a sailboat under a thunderstorm where the
strike rate/km^2 is hundreds of times higher. Because I know that the
strike rate in Fl is much higher than average, I'd want to double the
strike rate they give to be about 1/km^2/yr. This gives about a .7%
chance each yr of getting hit. Again, this does NOT address the
situation where you know the strike rate is much higer than average
(sitting under a storm). Based on math and observed strike rate, I
still think my estimate is good.

LIGHTNING STRIKE PROBABILITY
 

On 9 Jul 2004 10:29:26 -0700, (Parallax) wrote:

Strongest storms cover a larger area with greater wind. I have never
been in one of those but have watched them. The sky doesnt just get
dark, but turns a strange color. Intense strike rate for a few
minutes followed by a sudden increase in rain rate followed by a taper
off in wind and strike rate.

Parallax, of course you get the worst storms in Florida, but don't
think they don't happen elsewhere anywhere in N. America it gets warm
and humid.

We had tornados in northern Alberta a couple of days ago, and it's not
summer here in Toronto if there isn't a few monster squalls and/or
heat-driven thunderstorms that can spawn waterspouts and plenty of
lightning...

Thankfully, we don't have the duration or the frequency of Florida,
but short of hurricanes, the storms we get CAN be as violent.

BTW, that "strange colour" reference I recognize: it's the hallmark of
a vicious blow. First comes grey, greyer, greyest...then comes a sort
of gangrenous green flecked with black...THAT's the time to duck and
cover/deploy the storm jib/lash down everything! G

R.

LIGHTNING STRIKE PROBABILITY
 

pair of lox, a 5% chance of getting hit = a 95% of NOT getting hit.

A 5% chance of getting hit = .95 times .95 = a 90% of NOT getting hit even
once EITHER time in two tries.

a 5% chance of gettting hit = .95 times .95 times .95 times .95 = 81% of NOT
getting hit even once in FOUR tries.

by 8 tries the chance of NOT getting hit is only about 2 out of 3, by 14 tries
there is a better than even chance of being hit **AT LEAST ONCE**. by 30
tries, the chances of being hit at least once are 4 out of 5. by 50 tries,
chances of being hit at least once are greater than 15 out of 16. by 70 tries,
32 out of 33. by 90 tries, greater than 99 out of a 100.

that oak tree standing on the hill would be toothpicks by the end of the second
season.

Understand that in central Florida they receive more than 100 electrical storms
each year. a 5% chance of getting struck would mean central Florida has never
had trees.



How do you define "effective" area?
Your equation assumes that any lightning within the effective area of your
boat will strike your boat. If that were the case I'd be very afraid.

"Parallax" wrote in message
om...
Out of curiosity, I did a quick back of the envelope estimate of the
probability of a lone sailboat getting hit by lightning in a
thunderstorm.

...

I found a web site that gave a strike rate of about .5 strikes/km^2/yr
but they did not say where they measured this. However, this means
that a lone sailboat with a mast 17 m tall would have a .35% chance
each yr of getting struck. This is an ideal situation though and may
not address the situation of a sailboat under a thunderstorm where the
strike rate/km^2 is hundreds of times higher. Because I know that the
strike rate in Fl is much higher than average, I'd want to double the
strike rate they give to be about 1/km^2/yr. This gives about a .7%
chance each yr of getting hit. Again, this does NOT address the
situation where you know the strike rate is much higer than average
(sitting under a storm). Based on math and observed strike rate, I
still think my estimate is good.

LIGHTNING STRIKE PROBABILITY
 

"Parallax" wrote in message
om...
"rnh17" wrote in message
...
How do you define "effective" area?
Your equation assumes that any lightning within the effective area of
your
boat will strike your boat. If that were the case I'd be very afraid.

"Parallax" wrote in message
om...
Out of curiosity, I did a quick back of the envelope estimate of the
probability of a lone sailboat getting hit by lightning in a
thunderstorm.

...


As I said, effective area is defined as pi*9*(mast height squared).
This is comes from the distance over which a conductor over a flat
conducting plane (3* mast height) has minimal effect on the electric
field distribution(you know, the area of a circle being pies are
squared.

Do you have any equations for chance of getting bitten by a shark? But
seriously, I have no idea what you mean by "the distance...minimal effect on
the field distribution," but for the layman, why do you equate this with
lightning striking in that area?

LIGHTNING STRIKE PROBABILITY
 

But
seriously, I have no idea what you mean by "the distance...minimal effect on
the field distribution,"

no one else has any idea either.

for the layman, why do you equate this with
lightning striking in that area?

because pair of lox has an EE degree in physics. just ask him.

LIGHTNING STRIKE PROBABILITY
 

LIGHTNING STRIKE PROBABILITY
 

LIGHTNING STRIKE PROBABILITY
 

yup, pair of lox, there ain't no trees in central Florida, and none either in
Malaysia or Equatorial Africa. All blasted to toothpicks by lightning hundreds
of thousands of years ago.

I am pleased to see that JAX can multiply. However, my analysis
assumes a LONE sailboat (or other tall object).

Now, I found a site giving the strike rate for Malaysia and remember
that only two places have a higher strike rate than Central FL,
Equatorial Africa and SE Asia. Malaysia has a strike rate of
25/km^2/yr. I remember that C. FL rate isnt too much smaller than the
highest so I assume 10/km^2/yr and you get (using my effective area)
of a 7% chance/yr of a LONE sailboat getting hit. I find this to be
VERY believable based on experience.

JAX, not all lightning strikes kill and not all trees hit are killed,
most are not. Perhaps you just are not familiar with being in a high
lightning environment. Around here, I can go into the woods and find
MANY trees that have been hit by lightning. This is particularly true
of tall cypress trees.
I have found web sites calculating strike probability and they all use
a formula similar to mine where effective area goes as the height
squared. However, none i have found specify the factor by wich to
multiply the height to account for electric field modification, they
just qualitatively say it goes as height squared or use empiracaly
derived effective areas.

I still find my calculation to be very reasonable.

LIGHTNING STRIKE PROBABILITY
 

BE CAREFUL, PAIR OF LOX!!! YOU ARE GOING TO DIE A CRISPY CRITTER!!!!!!!

For further local perspective on the strike rate, consider that in my
own back yard of 1 acre, while I have lived here (15 yrs) three trees
have been hit with two being killed. My well enclosed in a shed was
struck. My neighbors well has been struck three times although it is
below ground. JAX, you just dont know lightning.