Net charge of the surface of the earth

[samueljun]

I am trying to understand why is the surface of the Earth negative. From the internet search, I found -10⁵ C. I make a sequence according to the conventional model and question at each step.

1. The surface is slightly negative: here I just accept and start.

2. Atmosphere is positive: Some internet source explains that friction of air or water, which seems that it should be net neutral. Only cosmic rays seem to be the reason for positive charge. Am I wrong?

3. 1800A of net electric current: This means the positive ions are coming down bit by bit due to the built in potentail between the surface and the atmosphere. Some explains that it is rain and dust causing 1800A of current. Which is right?

4. If the positive charges reach the surface of the earth, the net charge of the surface of the Earth must be already neutral (if the positive ions migrated due to the built in potential) or positive (if the positive ions came with rain and dust). It contradicts #1.

5. If the surface is positive, it is balanced by lightning making the surface "negative" again: how can more electrons come down or positive ions go up more than the potential between the cloud and surface becomes 0? In other words, lower surface of the cloud had electrons and these are recombined by the positive ions from the Earth surface. Than the electric field must be 0. Although there are more electrons up in the cloud, they cannot come down to make negative charge on the surface.

Could anyone explain clearly? Thanks!

 

[davenn]

see if this helps your understanding...

Re: what is the total net charge of the Earth's surface?
Date: Fri Oct 27 11:40:20 2000
Posted By: Jason Goodman, Graduate Student, Massachusetts Institute of Technology
Area of science: Earth Sciences
ID: 969209055.Es
Message:

I found viewgraphs for a lecture titled Lightning, Nature's Fireworks on the University of Alberta's website. This answers your question, plus many more related ones.

The solid Earth has a negative charge of about a half million coulombs. The atmosphere has a roughly equal and opposite charge, so that the Earth as a whole is roughly neutral. The charge difference produces a "fair weather electric field" in the lower atmosphere averaging about 6 volts per meter -- however, this field varies strongly with altitude, and is nearly 100 volts per meter at ground level. The total voltage difference between the ground charge and the atmosphere's charge (which exists roughly 30-50 km up) is about 300,000 volts. A simple calculation shows that the total energy stored in the fair weather electric field is 150 billion joules.

Since air isn't a perfect insulator, electrons leak from ground to air constantly, trying to reduce the charge difference to zero. This current amounts to 2000 amps. (Easy exercise for the reader: what's the resistance of the atmosphere?) Another simple calculation shows that the electrical power dissipated is 600 megawatts. This is the output of a large electrical power plant. While it's theoretically possible to harness this power for use by people, the fact that it's spread throughout the entire globe (to the tune of about a watt per square kilometer) makes it impossible in practice.

Since charge is constantly leaking between ground and air, there must be an "electrical generator" somewhere which is pumping electrons from air to ground, against the electric field. Thunderstorms are the generators. The movement of air and charged cloud particles within them separates electrical charges vertically; lightning then transfers the extra electrons at the base of the cloud to the ground. Positive charge at the top of the cloud leaks into the upper atmosphere. This recharges the fair weather electric field.

cheers
Dave

 

[samueljun]

Thank you Dave. It am more confused by reading the quote.

1. I thought 2000A of eath vertical electricity is due to ion coming down, not electrons leaving the earth.

2. From my internet search, lightning dissipates average 16 TW, which is 140,000 TWh per year. It is much more than 600 MW.

3. The the positive ion in the thunderstorm is spread -> electron comes up 2000A on a fine day but slowly due to air insulation. -> Earth surface is getting less negative charged -> there is no reason for lightning to come down.

4. It sounds like there is no contribution of cosmic ray in the atmosphere.

I have doubting about the conventional model. This is why I am picking on. Not personally against the post.

 

[davenn]

OK some things to consider

1) NOT ALL lightning is negative strokes down ... some are positive
2) NOT ALL lightning strokes are down ... some are upwards ~ 25% and again some positive and some negative
3) NOT ALL lightning strokes are between cloud and ground (and visa versa) a large % of them are intra-cloud
(within clouds)
4) There are massive discharges from the tops of storm systems that go up into the Ionosphere. These totally dwarf the cloud-cloud and cloud-ground discharges ... do some googling on Sprites, and Jets in the upper atmosphere

I spend a lot of time in the summer months storm chasing both here in Australia and also in the USA (when I have the time and money). And one thing I have observed over and over again is option 3

I couldn't find any internet references to your figures maybe you can supply some reliable references for me to check out

cheers
Dave

 

[samueljun]

Thank you for being active in the discussion.

10% of lightning is cloud to ground. This energy should be equal to 600 MW according to the quote. This means the total energy (causing lightning) in the cloud is around 6 GW. It is still far from 16 TW unless we change the claim that 10% of lightning is cloud to gournd.

I do believe thundercloud has much more power (energy) than 6 GW considering elve, sprite and so on.

Although we correct this (10%) part, still the question remains, how is the Earth negatively charged on a fine day? This should make 2000A current on a fine day, which should make the Earth neutral slowly. Lightning has nearly no reason to flash down because it is either negative or getting positive due to the positive ions coming down. And it this circle should stop some day.

Some people say it is inductive that the Earth becomes positive under the thunderstorm. This does not make sense either unless the core of the Earth is strongly positive. Dielectric behaviour is due to the coulomb force. If the net charge of the Earth is neutral, there is no net coulomb force to ionise the air.

I want those questions answered. To start with it I am asking, why is it negatively charged?

 

[davenn]

did you not read that ALL lightning is NOT cloud to ground ?
and any figures given will include all forms of discharge

why is what negatively charged ?

you haven't given any references yet to back up your quoted figuresDave

 

[samueljun]

Yes, I read and answered 10% is cloud to ground. I just read in wikipedia.

But this cloud to ground discharge (normal lightning) cannot be understood, thinking that the Earth surface is negatively charged. As I read, lightning from positive cloud to negative Earth is rare.

Sorry for the unclear statement at the end. It meant the question of the title. Why is the surface of Earth net negatively charged? In your quote, it is also written half million coulomb.

 

[samueljun]

In the meanwhile I found out the best document available in the internet.

http://74.63.154.231/here/wp-content/uploads/2013/06/Chevalier_electrical_surface_potential-2007.pdf

I am reading it carefully. What I already learned ist that

* the reason for the negative charge of the Earth surface is not known.
* hypothesis that lightning is balancing the negative charge to the Earth is 100 years old and it is not based on actual measurement but on the time calculation of the Earth field and lightning time. It is not well accepted now.

 

[Quincy cuff]

Why couldn't you just have a giant dc motor with one pole to 100 feet into surface ground and the other 100 feet into the atmosphere and essentially just convert lightning to kenetic energy then into usable ac current

 

[Baluncore]

Welcome to PF.
The insulation needed for the motor would need to be better than air since lightning has no problem with air. The inductance of a motor would delay the current rise and so result in an arc through the air. It would require an insulation medium such as Sulfur hexafluoride to displace the air. That would require a gas tight containment, with an insulated lightning rod connection at the top. SF₆ is a greenhouse gas.

 

[Quincy cuff]

Welcome to PF.
The insulation needed for the motor would need to be better than air since lightning has no problem with air. The inductance of a motor would delay the current rise and so result in an arc through the air. It would require an insulation medium such as Sulfur hexafluoride to displace the air. That would require a gas tight containment, with an insulated lightning rod connection at the top. SF₆ is a greenhouse gas.

So it would be complicated, but most definitely more plausible than trying to store the energy in high amp dc energy.

 

[Quincy cuff]

After the engineering of en electric motor to be able to take a hit from lightning and spin up you could then convert electricity into kenetic energy witch is way more sustainable.

 

[Baluncore]

After the engineering of en electric motor to be able to take a hit from lightning and spin up you could then convert electricity into kenetic energy witch is way more sustainable.

You are dreaming.
If the motor could spin up during the strike then the kinetic energy must be stored there in the motor at the end of the strike. To accelerate so quickly requires a very light motor. If the motor was so light that it could accelerate, then it's speed of rotation would have to be extremely high. It would be overbuilt for average strikes, or self destruct on bigger than normal strikes.

Many people have thought it possible to capture lightning energy for productive use. It is technically a very significant challenge. It is probably the most unreliable and unpredictable source of energy. It is an incredibly uneconomic investment, there are many better ways to harvest energy from the environment.

 

[rootone]

Prior to a lightning strike occurring a huge electrical potential is being produced.
In principle there might be a way of harvesting energy from that, without awaiting for an actual lightning discharge.
I guess it would need to involve some kind of a huge airborne capacitor though, so not really doable.

 

[Baluncore]

I guess it would need to involve some kind of a huge airborne capacitor though, so not really doable.

That is the fundamental problem we have now.
The "Earth–Ionosphere" is a huge spherical capacitor with the atmosphere as the dielectric. There is turbulence and instability in the dielectric. Every so often there is a failure of the dielectric, we call that failure lightning.

Unfortunately there is no good "upper conductor" overhead, only the ionosphere, so we cannot make a good electrical connection. If we draw any power we have to wait for the local dielectric to recover before we can harvest more power. The very act of harvesting energy from the atmosphere changes the charge distribution and potential field to make further harvesting even more difficult.