We Still Don't Know How Lightning Is Generated

[exchemist]

Due to a question asked on another forum, I tried to look into the mechanism by which charge separation takes place in thunderclouds. To my surprise it seems we still don't know how it happens.

 

I found this paper, summarising the various hypotheses and the drawbacks of each: https://www.researchgate.net/publication/227134643_Charge_Separation_Mechanisms_in_Clouds

Apparently the leading hypotheses are an inductive mechanism, relying on polarisation of liquid water droplets and one involving charge transfer between "graupel" (soft hail) and ie crystals.

The inductive hypotheses relies on the idea that the electric field within the cloud (+ve at the top and -ve at the bottom) polarises the larger droplets, which are falling under their weight, so that they become positively charged at their base. When they encounter small droplets, which are rising due to the convective updraught in the cloud, they abstract electrons, leaving the small droplets with a +ve charge.  So this leads to a further accumulation of +ve charge at the top and -ve at the bottom, further strengthening the electric field and so on.   

The ice one was more intriguing. Experiments at Manchester University have apparently shown that when falling lumps of graupel contact ice crystals, charge tends to be transferred, the extent and polarity of the transfer depending on the temperature. I found myself wondering why there should be a difference in tendency to lose electrons - or protons - (it is unclear which are the charge carriers in the interaction) - between crystalline ice and the presumably more amorphous ice in graupel. I wonder if it may be to do with the edges and vertices of crystals. There will be unsatisfied valencies there, since the molecules at such locations are not fully bound into the lattice in all directions. The paper doesn't go into this, being more concerned with the physics of the overall process. 

Anyway, it seemed interesting that this is not yet well understood. I wondered if anyone here might know more about the subject. 

 

 

Edited October 29, 2022 by exchemist

[dimreepr]

This is an interesting watch on the subject (hope you can view it).

[exchemist]

51 minutes ago, dimreepr said:

This is an interesting watch on the subject (hope you can view it).

It may be but it seems to address a different issue, viz. how the lightning discharge occurs. Does it actually discuss the mechanism of charge separation? I'm not going to waste time watching a video that may be irrelevant to what I'm trying to understand. 

[MigL]

Charge separation between the upper and lower parts of the cloud would indicate that the eventual discharge ( lightning ) would occurr within the cloud itself.
Most all lightning I've seen discharges between the earth and cloud, indicating that is where charge separation occurrs, and the mechanism would be similar to rubbing a balloon on your hair, or rubbing an amber rod with fur, or ...

The mechanism discussed in your link, may contribute, but it doesn't explain the lightning or its path.

[exchemist]

25 minutes ago, MigL said:

Charge separation between the upper and lower parts of the cloud would indicate that the eventual discharge ( lightning ) would occurr within the cloud itself.
Most all lightning I've seen discharges between the earth and cloud, indicating that is where charge separation occurrs, and the mechanism would be similar to rubbing a balloon on your hair, or rubbing an amber rod with fur, or ...

The mechanism discussed in your link, may contribute, but it doesn't explain the lightning or its path.

Cloud to cloud discharges are extremely common in thunderstorms.

But my interest is in the charge separation mechanism. Handwaving about the triboelectric effect (which by the way also seems poorly understood) doesn't seem to help very much. 

Regarding cloud to ground discharges, my understanding is that it is the charge separation within the cloud which causes a polarisation of the earth beneath and that is what leads to a lightning strike. I've never heard of any triboelectric effect involving the earth (what would "rub" against the earth and how would that work?).  

 

[MigL]

8 minutes ago, exchemist said:

how would that work?

Liquid water and ice, moving through the air, tend to build charge.

An example you may be familiar with ( if you were an industrial chemist ) ...
You never have a liquid like IPA, or Toluene, etc., free falling into a tank.
You should always have a dip-leg to prevent charge build-up

[exchemist]

1 hour ago, MigL said:

Liquid water and ice, moving through the air, tend to build charge.

An example you may be familiar with ( if you were an industrial chemist ) ...
You never have a liquid like IPA, or Toluene, etc., free falling into a tank.
You should always have a dip-leg to prevent charge build-up

From my experience in the oil industryI'm aware of static generation in insulating liquids flowing in a pipe or in charged droplets in water sprays, used in tank cleaning etc, but I don't believe I've come across the idea that liquid falling through air does this to a significant extent.

 

[Sensei]

Quote

We Still Don't Know How Lightning Is Generated

 This is how I do it:

 

 

Edited October 29, 2022 by Sensei

[studiot]

I'm sure this graph is relevent.

 

https://www.researchgate.net/figure/Breakdown-voltage-in-air-versus-relative-humidity-with-an-alumina-surface-Electrode_fig17_3165903

[exchemist]

50 minutes ago, studiot said:

I'm sure this graph is relevent.

 

https://www.researchgate.net/figure/Breakdown-voltage-in-air-versus-relative-humidity-with-an-alumina-surface-Electrode_fig17_3165903

What does this tell us about the mechanism by which charge separation takes place in thunderclouds?

[studiot]

15 hours ago, exchemist said:

What does this tell us about the mechanism by which charge separation takes place in thunderclouds?

There are too many pages to reproduce here (10) but if you let me have an email address by PM (I usually recommend setting up a special gmail account for this) I can let you have a copy of the current electro-physics explanation due to Maynard.

[Eise]

Kevin's Thunderstorm? See here, from Veritasium.

Are clouds with upgoing and downfalling drops and ice crystals not gigantic influence machines, so to speak wet versions of the Wimshurst machine?

Which, of course as nothing more than you suggest...

Edited October 30, 2022 by Eise

[exchemist]

1 hour ago, Eise said:

Kevin's Thunderstorm? See here, from Veritasium.

Are clouds with upgoing and downfalling drops and ice crystals not gigantic influence machines, so to speak wet versions of the Wimshurst machine?

Which, of course as nothing more than you suggest...

Nice. This seems to be the inductive model, more or less. 

[studiot]

2 hours ago, Eise said:

Are clouds with upgoing and downfalling drops and ice crystals not gigantic influence machines, so to speak wet versions of the Wimshurst machine?

Which, of course as nothing more than you suggest...

No I don't think so.

For a start that machine requires large continuous metallic conductors AKA wires in the sky.
Last time I looked I didn't see any.

Secondly you quite rightly identified upward movement as well as downward movement.
Again I don't see this in the machine.

But many thanks for bringing this gadget to my attention.
I had not heard of it before.
If you listen to others, you can learn somthing new every day.

+1

 

The Maynard model I referred to is the result of many measurements of the electric field at various altitudes and is used in the flying industry for calibrating navigation equiment.

It is a capacitive model.

It also has both upward and downward movement of particles.
It was the result of a geat deal of research in the decades mid 1940s to mid 1960s.

[exchemist]

28 minutes ago, studiot said:

No I don't think so.

For a start that machine requires large continuous metallic conductors AKA wires in the sky.
Last time I looked I didn't see any.

Secondly you quite rightly identified upward movement as well as downward movement.
Again I don't see this in the machine.

But many thanks for bringing this gadget to my attention.
I had not heard of it before.
If you listen to others, you can learn somthing new every day.

+1

 

The Maynard model I referred to is the result of many measurements of the electric field at various altitudes and is used in the flying industry for calibrating navigation equiment.

It is a capacitive model.

It also has both upward and downward movement of particles.
It was the result of a geat deal of research in the decades mid 1940s to mid 1960s.

Curiously, Maynard's name does not appear in the review of the various models that I linked in the OP. A lot of work has been done since the 1960s, so it may have been superseded.

Rather than sending me 10 pages by PM, is it possible for you to post a short summary of its key features?

[trevorjohnson32]

On 10/29/2022 at 7:28 AM, exchemist said:

Due to a question asked on another forum, I tried to look into the mechanism by which charge separation takes place in thunderclouds. To my surprise it seems we still don't know how it happens.

 

I found this paper, summarising the various hypotheses and the drawbacks of each: https://www.researchgate.net/publication/227134643_Charge_Separation_Mechanisms_in_Clouds

Apparently the leading hypotheses are an inductive mechanism, relying on polarisation of liquid water droplets and one involving charge transfer between "graupel" (soft hail) and ie crystals.

The inductive hypotheses relies on the idea that the electric field within the cloud (+ve at the top and -ve at the bottom) polarises the larger droplets, which are falling under their weight, so that they become positively charged at their base. When they encounter small droplets, which are rising due to the convective updraught in the cloud, they abstract electrons, leaving the small droplets with a +ve charge.  So this leads to a further accumulation of +ve charge at the top and -ve at the bottom, further strengthening the electric field and so on.   

The ice one was more intriguing. Experiments at Manchester University have apparently shown that when falling lumps of graupel contact ice crystals, charge tends to be transferred, the extent and polarity of the transfer depending on the temperature. I found myself wondering why there should be a difference in tendency to lose electrons - or protons - (it is unclear which are the charge carriers in the interaction) - between crystalline ice and the presumably more amorphous ice in graupel. I wonder if it may be to do with the edges and vertices of crystals. There will be unsatisfied valencies there, since the molecules at such locations are not fully bound into the lattice in all directions. The paper doesn't go into this, being more concerned with the physics of the overall process. 

Anyway, it seemed interesting that this is not yet well understood. I wondered if anyone here might know more about the subject. 

 

 

Hey Exchemist, hot handing my question from the other forum ay?

I think we need to look at the difference between non lightning rain clouds and lightning bearing rain clouds. Both are going to have friction in the clouds. Could perhaps the keys lie in the clouds reaching up to a higher level of ionsphere? Perhaps the heat from humidity rises and collects in the ionsphere and produces lightning that is attracted to the heavy metal on and in Earth?

The electrosphere layer (from tens of kilometers above the surface of the Earth to the ionosphere) has a high electrical conductivity and is essentially at a constant electric potential.

Storm clouds are 6-12 miles high.

So as gravity tapers off into the exosphere, it gets colder and probably more conductive, or it could be conductive from Earth's magnetic field, or a combination of the two, the clouds reaching up so high are like wires for the heat on the surface up into the colder regions, then the heat converts to electricity probably from running water through the conductive zones, or maybe something else, and of course then you get lightning.

Edited October 30, 2022 by trevorjohnson32

[exchemist]

1 hour ago, trevorjohnson32 said:

Hey Exchemist, hot handing my question from the other forum ay?

I think we need to look at the difference between non lightning rain clouds and lightning bearing rain clouds. Both are going to have friction in the clouds. Could perhaps the keys lie in the clouds reaching up to a higher level of ionsphere? Perhaps the heat from humidity rises and collects in the ionsphere and produces lightning that is attracted to the heavy metal on and in Earth?

The electrosphere layer (from tens of kilometers above the surface of the Earth to the ionosphere) has a high electrical conductivity and is essentially at a constant electric potential.

Storm clouds are 6-12 miles high.

So as gravity tapers off into the exosphere, it gets colder and probably more conductive, or it could be conductive from Earth's magnetic field, or a combination of the two, the clouds reaching up so high are like wires for the heat on the surface up into the colder regions, then the heat converts to electricity probably from running water through the conductive zones, or maybe something else, and of course then you get lightning.

Yes Trevor it was stimulated by the research I did on this arising from your question on the other forum. There are more scientists here, so there is more of a chance of getting further with the topic.  Suggest you read and learn, and refrain from outlandish speculations. 

Edited October 30, 2022 by exchemist

[studiot]

4 hours ago, exchemist said:

Curiously, Maynard's name does not appear in the review of the various models that I linked in the OP. A lot of work has been done since the 1960s, so it may have been superseded.

Rather than sending me 10 pages by PM, is it possible for you to post a short summary of its key features?

Shrug.

If I thought the 10 pages from Professor Kraus, Director of the Radio Astronomy Observatory Taine could be condensed I would have already don this.

Interestingly, I don't see a reference to Andreas Neuber, the author of my reference ot the rel humidity work in your link either.

 

3 hours ago, trevorjohnson32 said:

I think we need to look at the difference between non lightning rain clouds and lightning bearing rain clouds. Both are going to have friction in the clouds. Could perhaps the keys lie in the clouds reaching up to a higher level of ionsphere? Perhaps the heat from humidity rises and collects in the ionsphere and produces lightning that is attracted to the heavy metal on and in Earth?

The electrosphere layer (from tens of kilometers above the surface of the Earth to the ionosphere) has a high electrical conductivity and is essentially at a constant electric potential.

Storm clouds are 6-12 miles high.

So as gravity tapers off into the exosphere, it gets colder and probably more conductive, or it could be conductive from Earth's magnetic field, or a combination of the two, the clouds reaching up so high are like wires for the heat on the surface up into the colder regions, then the heat converts to electricity probably from running water through the conductive zones, or maybe something else, and of course then you get lightning.

Hello trevor.

There seems to be a deal of bad feeling spilling over from some other forums and you have posted some rather outlandish statements in other threads here.

I do not wish to get involved in such matters.

But I will just say that the post of yours I have just quoted is the only sensible one I can attribute to you.
You do need to understand further some of the statements in it though.

The electrosphere is conductive at D C.

Above it the ionosphere is also conductive but at radio frequencies.

In his book, Electromagnetics, Kraus deals with the electrical engineering of this pages 98 to 103 and pages 211 to 214.

Some of the material comes from the work of Maynard Hill (sorry @exchemist I missed the Hill bit)

https://www.jhuapl.edu/Content/techdigest/pdf/V05-N02/05-02-Hill_Electro.pdf

[Eise]

14 hours ago, studiot said:

For a start that machine requires large continuous metallic conductors AKA wires in the sky.
Last time I looked I didn't see any.

Oh, I nearly always see steel constructions in thunder clouds ...

OK, without joking, there is a nice subtle difference in Kevin's thunderstorm, and real-life thunderstorms. With Kevin, all the droplets fall downwards. So my guess is that this construction is needed, because otherwise the influence can not be self-amplifying. In real thunderclouds of course we have up- and down-streams, making steel constructions unnecessary. 

[exchemist]

1 hour ago, Eise said:

Oh, I nearly always see steel constructions in thunder clouds ...

OK, without joking, there is a nice subtle difference in Kevin's thunderstorm, and real-life thunderstorms. With Kevin, all the droplets fall downwards. So my guess is that this construction is needed, because otherwise the influence can not be self-amplifying. In real thunderclouds of course we have up- and down-streams, making steel constructions unnecessary. 

Indeed. If you read my description of the inductive mechanism in the OP, it explains how that can take place.

[studiot]

7 hours ago, Eise said:

Oh, I nearly always see steel constructions in thunder clouds ...

OK, without joking, there is a nice subtle difference in Kevin's thunderstorm, and real-life thunderstorms. With Kevin, all the droplets fall downwards. So my guess is that this construction is needed, because otherwise the influence can not be self-amplifying. In real thunderclouds of course we have up- and down-streams, making steel constructions unnecessary. 

That would be equivalent to claiming that because there are two streams in an electrolyte, the external wiring is unnecessary to make the cell work.

I agree that two streams are necessary but there is a whole lot more to it than that.

 

I would observe that exchemist's reference looks at the microscale and disregards the macroscale circuit.

Equally Kraus' conventional discussion looks at the macroscale and disregards the  microscale.

 

A further comment neither of these address the question of 'Where does the energy come from ?'.

A good place to start would be global meteorology.
I say this because it was in the same period of development that the mechanism for moving large quantities of energy from the tropics towards the poles is due to a handful of giant cumulus cloud structures at any one time and the internal mechanism of these clouds is most interesting and strangely relevent.

Sarah Dry   Waters of the World  (2019)

Chapter 5  Hot Towers  page 147 ff.

Edited October 31, 2022 by studiot