I'd like a few of you fella's to help me here.
It is a well known theory amongst us free thinking people that lightning does not merely strike the ground as a source to earth.
My experience with high voltages and also things I have seen on the Net, would suggest that there are "feelers", that run from the ground upwards, to where a direct strike will hit.
Hence golfers being hit, the time between the feeler going up and the actual strike is measured in Nano-seconds.
Does anyone prescribe to this same theory?.
Lightning is a nasty thing, the more we can do to keep it away from our houses, people and anything else that affects our lives,the better.
Mind you though, Lightning really only became a problem once we started having Electricity in our houses and with using metallic building systems.
Please feel free to put your spoke in here.

Mike.

Trumpy
You've got it about right. Negative charges build up in the cloud base, while positive charges build on the ground. The + charges tend to collect and extend up round high points in the landscape; trees, masts, people, buildings. The -ve cloud charges extend down as leaders, some 100-200 feet, and when one of these gets near enough, a surge of + charges rises to make a channel- this channel then triggers a current flow from the ground, provoking the lightning return stroke proper. So, do lightning rods on buildings serve the purpose of grounding the +ve charges to reduce the chance of a strike? I've always thought; how can a puny strip of copper running down a building carry the hundreds of Megawatts of a bolt?
Alan

sln.fi.edu/franklin/bells.html

Ben Franklin provided the answer in 1753!!

Alan

Trumpy, here is a very basic site that explains what happens, but like I said, very basic, it's atcually done for kids to understand.
http://skydiary.com/kids/lightning.html

Alot more goes into how, why and where lightning will strike.
Stuff like ions,isokeraunic levels, inductance, ect..

Roger Block's book is awesome on this, if you have the time to read over and over again. It's kinda confusing.

Another note on this,

The old saying "lightning never strikes the say spot twice", isn't very true.

I rememmber reading that lightning strikes the Empire State building an average of 30 times per year.

If I can find that link, I'll post it.

Dnk..
Thanks for that link, I never realised that the actual flash went upward,which goes to show you learn something new every day.
Blinking science teachers!
Alan

Lightning is so very interesting!!!

The Elect. Engineering Manuals Sittin' Up On My Shelves - Collecting Dust each have an entire section devoted to "What Is Thought To Be Correct - So Far" regarding the phenomena.

Stroke Leaders "Pop" out from both sides - downwards from highly negative charged Cloud formations, and upwards from Earth bound areas of high Positive charge concentrations.

The Earth bound surface areas directly below the Cloud mass become Positively Charged, due to the increasing Negative Charge levels "Pressed Against" the Earth areas, from the Cloud mass above.

Negative charges in the ground areas are repelled away, leaving Positive charged moles O' dirt (and attracting additional Positive charge carriers).

All this increases until the dielectric strength of the enviromental Air gets punctured - then at least two stroke leaders connect, resulting in a discharge path.

The connection brings in an initiating arc, then the Plasma is developed. The Plasma is commonly oriented in an increasing "Step" from Ground to Cloud (appears to begin at the ground and "run up to the cloud"), whereas the initiating arc pulses downwards from the cloud.

The arc comes first, then the Plasma is created - which "Pushes" against the surrounding Air as it increases in size, and consequently as it decreases in size, the Air rushes into the void space.
That's where the thunder comes from!

If you are in the field of influence prior to a discharge event, you will feel its Capacitive field effects (hair will stand on ends).
That is the time for you to hit the floor!!!

To sum things up:

Water "cracking" into Ice when it freezes, generates the abundant Electrical Energy
(actually there are some other factors - even discharges from ABOVE the Stratosphere Clouds shooting downwards to the cloud mass, but too much to cover!).

The Charges in Cloud masses become oriented with Negative ones towards the bottom of clouds, and + towards the top.

Charges increase as more Ice cracks from Liquid Water (the water loses a small mass when becoming solid - hence the resulting energy "output").

As charges increase in the clouds, the ground plane becomes the "Opposite Plate" of the "Capacitor" and has a resultant "+" charge.

As the charge levels become high (+2 to +5 KV / Meter), "Stroke Leaders" begin to "Reach" towards the opposite polarity (up from ground, down from cloud). The entire event is similar to a Capacitor - with the cloud base being the "-" abundant plate, the Earth being the "+" abundant plate, and the surrounding air being the "Dielectric" between the plates.

When the field strength / charge level, develope to a point which results in a potential difference of +15 KV / Meter, stroke leaders are long enough to make connections.

Many leaders connect, but the ones of best conduction result in the visible event blasts.

At the point(s) of highest conduction, the initializing arc "Smacks Together" via the leaders - tearing the dielectric strength at that location.
This is usually heard as a "Loud Hard Clap" followed with a "Ripping" like sound.
The rip sounds like it is coming down from the clouds.

After the arc is setup, the Plasma begins its "Pulses" against the surrounding air.

The Plasma pulses rise in strength, become somewhat stable as the charges begin to flow easilly, then as the clouds' charges decay, the pulses lose strength and eventually cease all together - marking the end of that complete event.

Plasma pulses may range from as little as 10, upto hundreds per an event.

As the Plasma flows, it makes a more conductive path, so more charges flow.
As more charges flow, the Plasma becomes more conductive path, so it increases in size.

The Plasma pulses outwards in strength against the surrounding air - which keeps it "In Check", and has an energy transfer involve (compressing the air requires energy - and the resultant sound generated - the Thunder, also requires energy).

When the energy state become "Neutral" (or at least close to it), the event is complete.

The entire process repeats as needed per imbalanced energy levels are developed.

Sorry to throw in such simple and quick & dirty descriptions here.
Also, my descriptions are somewhat "odd", likely due to it being years since I've discussed this stuff!

There's TONS more to study in this area of theory, so have fun!

Scott35

But not with a kite.
Alan

***Bump***

Bumping thread to life.

BTW: Mike (Trumpy);
Did any of the stuff I posted make sense?
Was any of it helpful / enlightening (sp??)?

Scott35

My understanding follows somewhat as Scott put it, as follows.
In a storm, clouds rotate much like a generator producing AC, and a state of strain exists between the top + and bottom -of the cloud formation (capcitor effect).With AC, the + end is short of electrons, so when the dielectric breaks down, the + end gets its supply from the - end, the strain is relieved and a flash results.
In other situations, a state of strain also exists between the clouds and the ground, which has an even greater supply of electrons, and when this strain breaks down, a strike results - logically from the ground up. We see the strike moving downward, but I believe this is due to the illumination of the ionised air - not the strike itself.
I take the point re the small strap of copper lightning conductors - and Ben Franklin's sterling work, which I assume took place during a quiet phase in the affairs of state - but they seem to work satisfactorily - and it is interesting to note that other skyscrapers in the area may not need to bother with lightning conductors as they can rely on the Empire State attracting any wayward strikes!

Hope this helps.

Ron Braggins - England

Guys, some one provide me a link to the info that states a lightning strike originates in the ground and goes to the cloud.

Everything I've read, always stated that the strike is from "cloud to ground" or cloud to cloud".

I've heard many times people argue over this "ground to cloud" theory, but I am never able to find anything that backs this up.

One more note, is the thunder we hear the air collapsing upon itself. When the bolt tears through the atmosphere, it vaporizes the air in its path, and then pushes the surrounding air outwards as it is heated up.
When the strike is done, the air collapses back together and that force of the air collapsing is the thunder.

Is that true?

Any help?

Dnk...........

Ben Franklin, 1706-1790,is one of my heros. ("Well done is better than well said.")- did just that. He did more than just invent the lightning conductor. He also invented bifocal spectacles, proposed watertight compartments in ships, invented the finest woodstove ever built ( his pattern still on sale), proposed the terms +ve and -ve to describe the direction electrons travel in a circuit, described a battery, but was unsure of its usefulness- ( he died 8 years before Volta 'invented' it), crossed the Atlantic 5 times, invented the odometer, showed that lightning was actually electricity, as well as his prominant place in the first Governments of the United States.
dnk. I'm still a bit confused about the up/down strike thing, but thunder is, I think, the air collapsing back after being shock-wave expanded by very rapid heating by the immense power of a stike. Our Science Master at school said lightning struck down, but then the bloody old fool thought that one day we'd get the Empire back! He even had a huge map ( 10FT x 6 FT) of the World on the wall with the US, (and about 90% of the other landmass) filled in Red, (the British Imperial Empire color, nothing to do with the Commies!!)
Alan

Alan, The only Empire I know of, Luke destroyed with his light saber.

(Bad American humor)


Dnk.......

Scott35,
Of course it made sense.
Yes, as always, it was!.
There's some really interesting comments here,
thanks to all that replied!.

Scott35 basically has it right. The difference in charge does try to poke its way across from both directions at the same time. Every time some of the charge flows across the gradient to try to make it to the other side, more charge comes in to take its place near the cloud or ground. Half way in between that won't happen nearly as much, so you won't see leaders just popping up in the middle, though there will be some gradient flow there.

The cloud is also lifting upwards. With a given charge, increasing the distance between the poles of the charge, which lowers the capacitance in farads, actually causes the voltage to go up. This is balanced by the breakdown voltage also going up due to the increased distance. But once there is a plasma connection established, that now extremely high voltage will spread that connection over a larger volume of cloud and ground, increasing the overall charge it can access, and hence a higher current (think of it as an available fault current, if you will).

Turbulence certainly influences where successful leaders can be established, as well as shorter and better paths like radio towers or trees. Updrafts and downdrafts also have their effects. It just makes it very unpredictable where the next connection will be.

Lack of turbulence can actually make things worse in a few cases. The most intense lightning strike I ever saw took place in a rain event that involved flat land, a flat cloud base, no horizontal movement, and three hours of very slow lifting and cooling. That strike, over a mile away, produced thunder strong enough to knock out a couple windows in the apartment complex I was living in then, and triggered every car alarm in the parking lot. Several people around at first thought a bomb had gone off (it happened 3 months after 9/11 so I presume people were still jittery).

As the storm clouds move along with the winds, their charge slides along above the earth, pulling the earth charge along with it. This flow of charge can actually cause damage on its own to wiring that is multiply grounded in the direction of storm travel. It can also result in some strange lightning, like one I saw which took a leap from the backside of a storm cloud 5 miles out into clear air and hit the ground where the storm used to be.

The charge gradient is actually established long before a cloud can even be seen. I've experienced a high voltage buildup in open clear air that in involved inch-long sparks jumping from the radio antenna on top of my car to the metal frame of the car. Through the AM radio I could hear the gradient discharges taking place (a periodic buzz that starts at a high pitch and goes down very low in a second or two). I immediately left that location. By the time I was 3 miles away and looked back, the first storm cloud had formed. Within 30 minutes it was a long storm line dumping rain and lightning.

Scott,
I can absorb all the lucid explanations you and others have posted, but my problems are twofold;-
In my casual observations of lightning, as a layman, I see the strike come out of the cloud to earth, but this may be an optical illusion. My other problem is that when I read Isaac Asimov's book 'The Left Hand of the Electron' many years ago, he stated that whoever (I forget who, probably not Franklin) finally designated +ve and -ve, he had to guess which way electrons travelled in a conductor, and got it wrong. Asimov stated that electrons travel
-ve to +ve. But the earth is positively charged. So which way do electrons go in a lightning strike?

Alan

Finally found Asimov's book hiding in the loft, and it was Ben Franklin's original guess notation for + & - that was chosen to set polarities. Another point, Scott, if the strokes are pulsing rapidly- do they have inductive effects on power lines close by, (apart from actually hitting them?). I assume that there are also magnetic fluxes occuring in a stroke, but can't find any references to induction effects on the net.
Alan

Alan,

Let me search the books for more data, then get back to you regarding this topic.

BTW, Good "Ol Ben Franklin sure had ..., err.. with lack of a better term:

"Testicals O' Steel"

(referring to flying Kite in electrical storm, attaching key to string, and with Kite in clouds, "observed" sparks jumping from key to his finger!)

The Guy was creating a nice path for Streamers to contact Ground based Stroke Leaders!
Lucky as heck there was no contact, or that would have (likely) been the last experiment for him.

Scott35

He did too! Philadelphia, June 1752:

"But, dreading the ridicule which too commonly attends unsuccessful experiments in science, he communicated his intended experiment to nobody but his son who assisted him in raising the kite.... At length just as he was beginning to despair of his contrivance, he observed some loose threads of the hempen string to stand erect, and to avoid one another, just as if they had been suspended on a common conductor. Struck with this promising appearance, he immediately presented his knuckle to the key and, let the reader judge of the exquisite pleasure he must have felt at that moment, the discovery was complete. He percieved a very evident electric spark."

Sir Joseph Priestley writing in 1767


Alan