Stepped Leader in Lightning

On September 13, I gave a short reply to JL on the iniation of a lightning stroke. Here is the text:

A stepped leader starts in the cloud and reaches towards the earth. When it gets close, a streamer reaches up from the earth. When it reaches the leader, a conductive path is formed that allows the discharge from the cloud to the ground. Here are some videos in slow motion:

Sprites, Jets, and Glowing Balls: The Science of Lightning

formatting link

How does lightning work? Where does it come from? | Weather Wise S2E2

formatting link

Lightning Strike at 103,000 FPS

- in Singapore

formatting link

Lightning in Super Slow Motion

formatting link

This left the question what is a stepped leader? I came across an article that gives a good description. I'll give the text here, but check out the link. It has good pictures that explain better.

"Inside a thunderhead, electrical charges become separated. Warm updrafts sweep positive charges aloft, leaving the bottom of the cloud negatively charged. The attraction between the ground and the negative charges in the bottom of the cloud creates the lightning stroke, a brief current of negative charge that travels from cloud to ground.

The awesome power of the lightning stroke originates in the thunderstorm cloud where charges somehow become separated. There are several complicated theories that try to explain the actual mechanism of this charge separation, but no one really knows what pulls the charges apart in a thunderstorm cloud. It is believed that somehow water drops in the cloud become negatively charged and, being heavier than the surrounding air, fall to the bottom of the cloud. Meanwhile, the positive ions left behind are swept upward to the top of the cloud by the warm updrafts within the thunderhead. As more and more charges separate, parts of the cloud become so highly charged that the electrical forces tear nearby air molecules apart, making more charged fragments.

Since the ground beneath the cloud has far fewer negative charges on it than the bottom of the cloud, there is an attraction between the ground and the bottom of the cloud. Therefore, any electrons liberated near the cloud are pulled down toward the ground. As these electrons move, they bash into air molecules that are in their way, breaking the molecules up and creating more charged fragments. All the new negative fragments are dragged downward along with the original electrons and we have the makings of an electrical avalanche.

The avalanche would continue unabated were it not for the heavier and more sluggish positive charges that are left behind. They tend to attract the accelerating army of electrons back toward the cloud.

But more electrons are continually being liberated up in the cloud, and they stream to the rescue of the slowing electrons below, reinforcing their race downward. This process of electrons slowing and then being rescued by reinforcements repeats itself over and over again.

Stepped Leader

The initial party of electrons makes its way in jerky 150-foot steps along a sinuous path toward the ground.

This initial exploratory mission forms what is called a "stepped leader," named for its start-stop motion. The stepped leader takes about 5/1000 of a second, moving at about 240 miles per second, to reach from cloud to ground. When the leader gets near the ground, it may draw a stream of positive charges (called a streamer) up from the ground to meet it. When either the stepped leader reaches the ground or a streamer runs up to join the stepped leader, an electrical connection is completed between the cloud and the ground.

The ionized air molecules of the leader conduct electricity quite well, and the path of charged particles acts as a wire, connecting the highly negative cloud and the positive ground. This ionized air becomes the path of the main bolt of lightning.

The first charges to feel the connection are those near the ground.

The light and mobile negative charges quickly accelerate along the wire of ionized air. In their mad rush to the ground the negative charges collide with the air, causing it to glow like a neon sign--only thousands of times brighter and with a bluish-white color. The air near the ground is the first to start glowing, but as the electrons further and further up feel the connection and begin to accelerate, the air further and further up also starts to glow.

Even though the negative charges all move from cloud to ground, the bright flash of lightning moves from ground to cloud in a speedy

1/10,000 of a second, moving 61,000 miles per second! The super-heated air expands outward explosively, producing the shock wave we hear as thunder. The bright flash of glowing air is called the return stroke since it moves from ground to cloud, opposite to the moving charges.

The return stroke discharges a region of the cloud, but the cloud can reorganize quickly and as many as 40 strokes have been observed to use the same charged channel. If you've been told that lightning never strikes twice in the same place, don't believe it! Lightning usually strikes more than once!

There is quite a lot of energy in a lightning stroke, about 250 kilowatt-hours. At the current cost of energy, this would be about $16.75 worth. Doesn't sound like much, but with that amount of energy, you could lift a 2000-pound car 62 miles high!

Lightning doesn't always travel from cloud to ground. If two parts of the cloud are charged highly (and oppositely), a lightning bolt can actually occur inside the cloud. Lightning can also arc from one cloud to another.

lightning strike

The typical type of lightning is called streak lightning, or forked lightning. (Photo to the right from NASA - Marshall Space Flight Center.) If the lightning channel is blown by the wind during a multiple discharge, each succeeding stroke is displaced by a short distance, making it appear as ribbon lightning. On rare occasions the lightning seems to break up into beads that persist for as long as one second, an unexplained form called bead or chain lightning.

Sometimes the lightning flash is obscured by clouds, which are then brightly illuminated. During this sheet lightning, the flash seems to come from everywhere. The most controversial form of lightning is ball lightning. Ball lightning has never been observed scientifically and many doubt its existence altogether. It is reported to occur with or right after a nearby lightning stroke and is described as a luminous ball of light that floats along fences, rooftops, or through the open air. The jury is still out on ball lightning.

formatting link

Reply to
Steve Wilson
Loading thread data ...

It's impressive that nobody understands lightning.

Ground strikes can be positive or negative.

Reply to
John Larkin

[...]

It's improving. I used to think a lightning bolt had to cover the entire distance from the ground to inside the cloud, perhaps trillions of volts.

The stepped leader is a much better explanation. The ionized channel behind the leader is conductive, so it greatly reduces the voltage necessary to form a lightning bolt.

The steps occur in jumps of about 150 feet, so the breakdown only has to go that far. Still takes a lot of voltage, but not nearly the miles of the previous understanding.

Reply to
Steve Wilson

Don't be silly! Avalanche in solids (like a Zener diode) or gasses (Geiger tubes, to name the old examples) are well-studied in a variety of materials and regimes. Nobel Prize 1992 went to Georges Charpak for this subject.

Large scale and atmospheric chemistry are... minor details.

Reply to
whit3rd

Last I read there were/are uncertainties in the charge separation mechanism.

George H.

Reply to
George Herold

The common phrase in the Wiki article on lightning is "For reasons not well understood,..."

The x-ray and gamma radiation from lightning aren't understood either.

--
John Larkin         Highland Technology, Inc 

Science teaches us to doubt. 
 Click to see the full signature
Reply to
jlarkin

iger tubes, to

regimes.

It's stinking hot plasma. Even if the X-rays and gamma rays were just the h igh energy tail of a thermal distribution of emitted photons, they wouldn't take much understanding. As it is, you've got ionised atmospheric gases - including water vapour - and free electrons (which do most of the conductio n since they move faster than the - much heavier - ions).

We may not understand it in terms of having a detailed species-by-species i nventory of the ions and electrons in the hot channel, but there's no parti cular mystery about seeing the the occasional high energy photon get emitt ed.

--
Bill Sloman, Sydney
Reply to
Bill Sloman

A major mystery was how the lightning leader is initiated inside the storm cloud - i.e., what starts the initial spark breakdown process. The measured E-fields in thunderstorms are too low to trigger the avalanche breakdown processes that are necessary for initial spark breakdown and stepped leader formation. It now appears that cosmic ray showers play a role by creating showers of high-energy electrons ("runaway electrons" that initiate the avalanches that culminate in streamers and then leaders.

Reply to
Bert Hickman

What article are you referring to?

A great deal is understood about lighting, from high speed videos to actual flights inside thunderstorms. A more generous term might be "details are still being studied". See Wikipedia

formatting link

See Also

formatting link

Thunderstorms and lightning are fascinating topics. As engineers, it behooves us to learn as much as possible in order to minimize the destructive effects of nearby strikes.

Reply to
Steve Wilson

I have heard the same thing also. An additional effect is noted in the jerky and random changes in direction of the stepped leader due to cosmic rays.

Reply to
Steve Wilson

On a sunny day (Thu, 01 Oct 2020 19:09:05 GMT) it happened Steve Wilson wrote in :

I have seen ball lightning face to face in my high-school years. One day, just after I placed an FM reception dipole on the neighbors roof, a big lightning storm started. Told him to disconnect the antenna, I was on the first floor, the other neighbor below us had a long wire antenna in his garden.

I had the window open, looking at the lighting... After some bang a big white ball, about 30 cm or so in diameter, appeared and hung before the window. Looked at it face to face, from maybe about 1 meter distance, no heat coming from it. It hung there a few seconds, and then slowly started sinking and a load bang happened. Next morning went to look at the antenna in that garden, was between 2 trees, only 2 black burned ends were left, the ball evaporated it. Look up Murat Ozer electron black hole:

formatting link

I was almost a magic experience, sort of 'will it come to me or?' well, I take it as nature showing me something, plenty of discussions in sci.physics about that years ago.

Reply to
Jan Panteltje

PS that was in the days when we were experimenting to control things with our thoughts. Take it as sign to me perhaps, Had some experiences before that, this was a day or so after that. Everything is connected.

We really know shit. :-)

Reply to
Jan Panteltje

This looks OK. Many of the hits I got searching google were for papers from the 60-80's.

formatting link

George H.

Reply to
George Herold

But not much else.

Reply to
John S

Avalanche diodes are NOT Zener diodes. Prof. Zener even sued against his name being used for this. They settled to call them Z-Diodes and attribute it to the form of the curve.

Cheers, Gerhard

Reply to
Gerhard Hoffmann

On a sunny day (Fri, 2 Oct 2020 08:28:48 -0500) it happened John S wrote in :

plonk

Reply to
Jan Panteltje

ger tubes, to

egimes.

What are sold as "zener diodes" ranges from actual Zener diodes which have breakdown voltages below 5V to avalanche diodes which break down above this .

Around 5V both mechanisms. are going on in parallel. Low voltage regulato r diodes in which the Zener mechanism is dominant have a negative temperatu re coefficient, while higher voltage regulator diodes have a positive tempe rature coefficient, but if you want a low temperature coefficient regulator , a roughly 5.6V avalanche diode in series with a forward biassed diode - a s in the 1N821 to 1N829 series - is the usual choice, giving you a distribu tion between 5.89V and 6.51V centered at about 6.2V at 7.5mA. If you want to get stability you pay for in a 1N829, you have to be very careful to kee p the current very closes to 7.5mA

I don't think that anybody gets too excited about the name.

--
Bill Sloman, Sydney
Reply to
Bill Sloman

Everybody calls them zeners.

That sure didn't last long.

--
John Larkin         Highland Technology, Inc 

Science teaches us to doubt. 
 Click to see the full signature
Reply to
jlarkin

Am 02.10.20 um 17:48 schrieb snipped-for-privacy@highlandsniptechnology.com:

Just a case of honesty. Does not fit into today's world.

Gerhard

Reply to
Gerhard Hoffmann

What should we call a 5.2v diode?

Zenalanche? Avazar?

Should Digikey have three catagories?

--
John Larkin         Highland Technology, Inc 

Science teaches us to doubt. 
 Click to see the full signature
Reply to
jlarkin

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.