You know, I'm a strange guy... I think I should have been a scientist instead of a cruiser because I really study these things for no other purpose than my need to know how it works. This often makes me skip details in my posts and they still end up very long posts ;-)
So, here we go; I'll be blunt sometimes but be assured that it isn't personal... it's how engineers talk to each other ;-)
Seriously what is a leader or a streamer in terms of accepted physics. Are they particles (atoms etc), forces, can they be measured, can laws be ascribed to them. If not, then they may well be meaningless.
Both leader and streamer are fully understood and documented. They have recorded them with high speed filming and you can do experiments yourself with a Van De Graaff (Dutchman of course ;-) generator
, where the streamers form from your fingertips and the leader from the generator
. They are indeed ionization of air, plasma. The plasma is conductive and this forms the electrical path for the lightning strike.
So, when you look at lightning you often see many many leaders coming down (branching) from the sky, like the roots of a plant. Only one or sometimes two reach the earth. The ones that don't reach the earth
are the leaders and the top part
of the ones that do reach the earth are the leaders. The bottom part of these are the streamers. You see the leaders that don't reach the earth because they discharge into the path that connects to earth first... they supply power to it just like the cloud
. The leaders and streamers are visible when filmed with high speed film as a purple glow... just like St Elmo's fire... you actually see plasma.
As the leaders work their way down while ionizing the air, their presence (they are highly charged) triggers the streamers to form from earth upwards. These are the ones that form from high and sharp points and that can be a brush, carbon-crystal but even tips from leaves on a tree. It is all about the moment when a streamer meets and connects with a leader (they attract each other because they have opposite charges)... now there is that conductive path from cloud to ground and the strike occurs. Many strikes through that same path follow, sometimes so quick you see it as one strike or maybe two or some flickering (there's dozens in reality). The nice thing is that the leaders that didn't make it only flash with the initial strike as they discharge themselves into the path to earth. I have actually seen a single
plasma path used over and over for minutes with pauses of up to 20 seconds or so. All the repeat flashes are just the single channel without branches.
To read up on this there is Wikipedia but I also like the "How Stuff Works" site. Here is the page starting with the ionization process... the next pages describe the leaders and streamers etc.: HowStuffWorks "Ionization"
So, there are no questions about if this is what really happens with lightning. The unknown part is how exactly the cloud gets charged because there are multiple theories that make sense. I think the ice-crystals (they melt and freeze over and over) moving up and down in the cloud create it but there are much juicier theories too.
This appears to be a description of the ionization process of a gas. I don't believe an object on the ground "breaks down and emits streamers". No description of any object I have ever heard about states it contains "streamers" which can be emitted when influenced by large electrical fields.
Blunt mode on: it isn't relevant if you believe this, it's how it is regardless of what you believe ;-) When you see St Elmo's fire in the rigging
you are watching the rigging
and surrounding air breaking down. Don't think the steel
wire is breaking apart, "breaking down" must be read as in how an magnetic field can break down
, i.e. it gets ionized. It is not about metal or air breaking apart.
If I understand the point correctly, it says a sharp point will ionize at a lower potential and therefore the streamer will be shorter. This would seem to indicate that the sharp point would be struck more often given that ionization has to occur for the low resistance current path (strike) to be established.
We're getting very close now ;-) Indeed, a sharp point starts ionizing surrounding air sooner (at a lower level of charge which is earlier in time
) than a blunt point. But that doesn't mean it gets struck more often. This is exactly why they started making lightning rods with blunt points or even balls on top. The sharp point starts sooner, when the charge isn't high enough for a large leader to form yet. As the point starts ionizing, it bleeds the charge off, while other objects only build up at that same moment in time. Now, when the charge gets high enough it's time to start the race
for who can form the highest leader and the sharp point looses because blunt objects have "saved their charge" earlier.
Yet here, it is suggested that the ionized gases stop a "streamer". What is happening here, earlier we had a streamer meeting up with a leader and an ionized channel becoming a path for the strike. Now we have ionization occuring before the streamer meets the leader and effectivly preventing the two meeting to develope an ionized channel. This sounds like a "Catch 22" - you have to have ionization occuring to prevent ionization occuring.
No, it doesn't stop the sharp object from forming a streamer. But the streamers from the sharp objects are smaller as they lost
part of their charge earlier. The moment in time they ionize while blunt objects don't do that yet is the same as the wicks on aircraft even though that charge is from a different source. Also, a sharp point doesn't "bleed ions" better or in a bigger volume compared to blunt objects... they start doing it earlier at a lower level of charge at an earlier moment in time... and while doing so, they loose part of their charge while blunt objects save it all for later.
There is no logic here, it makes a case for something to be true when the premise is (at the best) suspect and not proven. If there is only a slightly different view taken then the argument is reversed i.e. A sharp point "breaks down" at a lower potential and therfore is more likely for an strike to occur at the sharp point.
The logic becomes obvious when you realize that the charge builds up as the cloud moves closer
. The sharp point starts ionizing at a time that the leaders aren't close enough or far enough down yet to connect to it's little leader.
The whole thing makes sense and it will really works... the question is if it will work good enough, i.e. if the little brush really makes a difference. In a really violent lightning storm I think all bets are off. We have seen some horrific stuff like a horizontal lightning bolt that passed under the boom, striking the water
hundreds of yards further on. Try to explain that... we didn't even had the brushes
yet at that time. Our neighbors here had a lightning storm so bad that the husband was hiding under the salon
table and the wife saw Elmo's fire coming down the mast
and traveling over the boom right in her face! She yelled so loud for help on the VHF
that the coastguard copied them 125 miles out from California
... but that's more for the max. VHF
range thread ;-)
So, does it work enough to make a difference? I think they do, statistics will tell us. I challenge anyone to come up with an incident where lightning struck the masthead of a boat that had a static dissipater which was installed correctly (bonded to ground).
Every example I received over the last 4 years turned out to be an incorrect installation
... even dissipaters screwed onto a wooden mast
, like it was some kind of magic wand. Start asking around and check details and you will collect a significant amount of data over the years like I did, so you can form the same opinion... or not... let me know ;-)
It's time people stop thinking of these as magic wands because their enthusiastic stories have nothing to do with it and confuse others who prefer a more scientific approach. It puts many people off when they hear about the magic and they discard them, calling them snake oil
as the result. It might te true that they don't work well enough, my personal statistics gathering is too small for any form of conclusive evidence, and I don't record
it professionally anyway, but the brushes
will really "bleed ions" before any other part of the boat does so with all that I wrote above as the result... only the quantity and if that is enough is what I am not sure of.