ECN Forum Forums Technical Discussion Electrical Theory and Applications Lightning Theory

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