What is the net charge on the Earth?

[CWatters]

As I understand it Cosmic rays are mostly protons which have a positive charge. If the overall charge state of the Earth remans neutral is there a similar outflow of positive charge or a source of incoming negative charge?

Google wasn't very helpful.

 

[Baluncore]

If the overall charge state of the Earth remans neutral is there a similar outflow of positive charge or a source of incoming negative charge?

Well that is an interesting question.
As I understand it... When the solar wind reaches Earth's magnetosphere the wind is magnetically deflected around the Earth.

The solar wind is composed of ionised hydrogen = ( protons and electrons ). Each takes a different charge dependent trajectory through Earth's magnetic field. The majority of the mass is in the protons, so they are harder to deflect than the electrons, so more protons reach the Earth's surface. That suggests Earth's surface should be positive relative to a negative ionosphere, which is NOT the case.

Since the Earth's surface is screened from space by the conductive ionosphere, the positive ionospheric polarity relative to the negative ground must be more a function of atmospheric processes than the solar wind. We reference ground as zero volts, and the ionosphere as being charged positive simply because we have our feet on the ground.
I would expect the external charge on the Earth, relative to the solar wind to be neutral, like the wind. Any significant deviation from neutral would distort the partition of charge in the solar wind passing the Earth. Electrostatic deflection would regulate the external charge on the Earth's ionosphere.

 

[CWatters]

Thanks. I should have realized that the solar wind is much more significant than cosmic rays.

 

[anorlunda]

But every time we see an aurora, it means charged particles entering the atmosphere. I don't know if those particles are net positive, negative, or neutral.

I suspect but don't know, if there are mechanisms for charged particles to leave Earth.

I believe that this thread will get better answers in Astronomy and Astrophysics. I'm going to move it there.

 

[CWatters]

I think what Baluncore is saying is that if the Earth had a net positive charge due to cosmic rays then positive particles in the solar wind would be deflected and negative attracted. This would restore charge neutrality.

I don't think cosmic rays would be deflected as they are very energetic but solar wind is much slower (I think).

 

[fresh_42]

I think what Baluncore is saying is that if the Earth had a net positive charge due to cosmic rays then positive particles in the solar wind would be deflected and negative attracted. This would restore charge neutrality.

I don't think cosmic rays would be deflected as they are very energetic but solar wind is much slower (I think).

I'm also interested in an answer. Where do all the proton charges go to? Perhaps they are simply too few to have any measurable effect, or they ionize existing atoms and some electrons leave the Earth system, although this seems unlikely. I've found many pages about secondary cosmic rays, the calculation of energies, the kind of decay processes and so on, but nothing about the charge balance. So is Earth an anode?

 

[anorlunda]

Can we pose the question this way. Suppose the Earth acquired a net charge, either plus or minus, the mechanism unspecified. Then what are the mechanisms to return it to neutral? It would be strange if the solar wind was the only mechanism.

But if there was no mechanism, then net charge could build up indefinitely and that sounds unlikely.

Edit: Related, here's a post from @davenn about lightning between Jupiter and its moons. https://www.physicsforums.com/threads/can-a-spark-form-through-vacuum.630710/#post-4047029

 

[JMz]

To anorlunda's point, if the Earth acquired a net charge, whether from a solar flare or cosmic rays, then the solar wind would almost certainly neutralize it: The Earth would attract more of the opposite charge from it, repel more of the like charge, and even (I suppose) expel a few like-charged ionospheric ions into the solar wind. The net result would be to restore neutrality.

 

[davenn]

To anorlunda's point, if the Earth acquired a net charge, whether from a solar flare or cosmic rays, then the solar wind would almost certainly neutralize it: The Earth would attract more of the opposite charge from it, repel more of the like charge, and even (I suppose) expel a few like-charged ionospheric ions into the solar wind. The net result would be to restore neutrality.

have you got some references for that, please

 

[stefan r]

I thought sprites exchange electricity with space. I do not know how much exchange takes place during calm weather.

You cannot track electrons. There is no compound, element, or isotope. There can never be a paper that says "We measured x% martian electrons in this batch of plasma". All plasma's have the same electrons. We can see the effect of electrons moving. Electricity can flow via vacancies. A cosmic ray colliding with Earth adds a vacancy. Holes may not do anything we can easily see.

I suspect a space elevator on Mars could provide some sort data.

 

[Baluncore]

have you got some references for that, please

The currents flowing between the Solar Wind, Magnetosphere and Ionosphere are called Birkeland currents. They go both ways, all the time.

Start here; https://en.wikipedia.org/wiki/Birkeland_current There are references at the bottom of the page.

See also; "The solar wind‐magnetosphere‐ionosphere current‐voltage relationship" - JA Fedder, JG Lyon - Geophysical Research Letters, 1987.

 

[davenn]

I thought sprites exchange electricity with space.

no, they got between the tops of thunderstorms and the ionosphere

 

[stefan r]

no, they got between the tops of thunderstorms and the ionosphere

The sprite's glow is in the mesosphere. Normal lightning connects a cloud to the surface. We do not see underwater lightning but you can still get electrocuted while swimming. You will not find an pile of electrons in a tree that got struck by lightening. The bright bolt of a lightning is ionized air which glows because the electricity passed through it. The ionosphere is already partially ionized.

 

[davenn]

The sprite's glow is in the mesosphere. Normal lightning connects a cloud to the surface. We do not see underwater lightning but you can still get electrocuted while swimming. You will not find an pile of electrons in a tree that got struck by lightening. The bright bolt of a lightning is ionized air which glows because the electricity passed through it. The ionosphere is already partially ionized.

that is just a word salad ... doesn't even begin to make sense

 

[stefan r]

that is just a word salad ... doesn't even begin to make sense

Probably right about the wording. Is this article better?
Section 3:

Thunderstorms directly couple the atmosphere and the ionosphere...

...charge state of the Earth remans neutral is there a similar outflow of positive charge or a source of incoming negative charge?...

The Earth is negatively charged. Lightening builds up the potential gradient.

 

[Baluncore]

The Earth is negatively charged. Lightening builds up the potential gradient.

The Earth is only negatively charged relative to the Ionosphere.
Lightning does not build up the Earth-Ionosphere charge and gradient, it tends to reduce or discharge it.
The charge build up across the atmosphere is modeled as the “fairweather current”.
https://en.wikipedia.org/wiki/Global_atmospheric_electrical_circuit

 

[JMz]

Eyes on the OP: I believe the "Earth", as referred to in the OP, included the atmosphere, not only the solid part. (@CWatters - agreed?) Weather is just part of that system and doesn't change its net charge.

 

[stefan r]

As I understand it Cosmic rays are mostly protons...

Eyes on the OP: I believe the "Earth", as referred to in the OP, included the atmosphere, not only the solid part. (@CWatters - agreed?) Weather is just part of that system and doesn't change its net charge.

Is there any reason to believe more protons hit Earth than electrons hit Earth? Detectors on Earth are usually on the solid part.

 

[Let'sthink]

I had read somewhere most probably in Halliday Resnick book 2nd edition that Earth has residual negative charge which creates an electric field pointing towards the centre of the earth.

I have an hypothesis cosmic rays contain gamma rays which give rise to positron electron annihilation pairs. Positrons have a limited life time and hence will annihilate with electrons in the atmosphere and the fast moving electrons would reach the Earth surface and deposit there.

 

[snorkack]

To anorlunda's point, if the Earth acquired a net charge, whether from a solar flare or cosmic rays, then the solar wind would almost certainly neutralize it: The Earth would attract more of the opposite charge from it, repel more of the like charge, and even (I suppose) expel a few like-charged ionospheric ions into the solar wind. The net result would be to restore neutrality.

No, it shouldn't.

If there is any sort of effect that preferentially gives Earth one charge or other, such as the suggested one of electrons being deflected by magnetic field but protons continuing by their greater inertia, then the charge would not build up indefinitely. A fairly small net Earth charge would cause Earth to attract more of the opposite charge and repel more of the like charge, indeed. But the net effect cannot be to restore neutrality, because as Earth approaches neutrality, this effect should diminish and disappear completely at neutrality, while the effect conferring charge on Earth would remain.
Rather, the net effect should be to stabilize Earth on a small but nonzero electric potential matching the electromotive force applied on Earth.
What is it?

 

[JMz]

I can speculate that more cosmic-ray protons than cosmic-ray electrons might penetrate the magnetosphere for mass reasons -- though both are so highly relativistic that their rest masses are only a small part of the total, so that's probably a very small effect. But again, the solar wind would quickly neutralize any net charge that managed to build up.

 

[snorkack]

But again, the solar wind would quickly neutralize any net charge that managed to build up.

No. The solar wind should create some charge.
Faraday did, in 1832, predict that the flow of conductive salt water of Thames through Earth magnetic fields should set up electric fields. He did not have adequate measuring devices.
Wollaston, in 1851, did measure electric field in telegraph cables caused by currents of English Channel in magnetic field.
Just like conductive seawater flowing in Earth magnetic field causes modest but nonzero electric fields, conductive solar wind flowing in Earth magnetic field should cause nonzero electric fields.

 

[JMz]

No, it shouldn't.

If there is any sort of effect that preferentially gives Earth one charge or other, such as the suggested one of electrons being deflected by magnetic field but protons continuing by their greater inertia, then the charge would not build up indefinitely. A fairly small net Earth charge would cause Earth to attract more of the opposite charge and repel more of the like charge, indeed. But the net effect cannot be to restore neutrality, because as Earth approaches neutrality, this effect should diminish and disappear completely at neutrality, while the effect conferring charge on Earth would remain.
Rather, the net effect should be to stabilize Earth on a small but nonzero electric potential matching the electromotive force applied on Earth.
What is it?

I agree with this point: The charge will not build up indefinitely, but any large effect will be neutralized by the solar wind, and the equilibrium will be reestablished at some level. There is no particular reason to think that that level will be zero.

 

[stefan r]

...Earth on a small but nonzero electric potential matching the electromotive force applied on Earth.
What is it?

NASA says

The field is about 100 volts per meter, meaning that the electric potential increases by about 200 volts from the ground to the top of Michael Jordan's head when he's standing still

A physics factbook says:

Surface Potential Gradient (PG) E 120 V.mE-1

Somewhere in the range of 100 to 120 V/m.

 

[JMz]

That's an atmospheric effect, isn't it?

 

[hutchphd]

The Earth is only negatively charged relative to the Ionosphere.
Lightning does not build up the Earth-Ionosphere charge and gradient, it tends to reduce or discharge it.
The charge build up across the atmosphere is modeled as the “fairweather current”.
https://en.wikipedia.org/wiki/Global_atmospheric_electrical_circuit

The article you quote says exactly the opposite I believe. Please look again

 

[Baluncore]

The Earth is negatively charged. Lightening builds up the potential gradient.

No. Thunderstorms actually build up the potential gradient, lightning reduces it. Do not trust wikipedia.

The article you quote says exactly the opposite I believe. Please look again

I am sorry, I was referring to the fair-weather part of the circuit. Many have edited the article who do not understand the circuit and there is a real tangle of confusion between the “generation by thunderstorm” and the “discharge by lightning” processes. Those processes are clearly working against each other.

The introductory sentences in some of those sections of wikipedia have it backwards.

To clarify;
Thunder storms generate a net positive charge in their head, at the top, opposed by a net negative charge in the mid-lower part.
The bottom of the cloud is charged positive relative to the Earth's surface.
Those two capacitor layers are polarised in the same direction, positive up, as is the Earth-Ionosphere capacitor.
Any lightning discharge of either charged capacitor layer will counter the charge imbalance and reduce the vertical voltage gradient.

 

[JMz]

But either way, it doesn't change the net charge of the Earth (as a planet, not only the solid part), which was the OP's question.

 

[Baluncore]

[Moderator's note: off topic comment deleted.]

But either way, it doesn't change the net charge of the Earth (as a planet, not only the solid part), which was the OP's question.

Correct. There is little influence on the ionosphere from the atmosphere below the cloud base.

 

[davenn]

[Moderator's note: off topic comments deleted.]

References provided:

http://iopscience.iop.org/article/10.1088/0143-0807/24/5/305/pdf
http://users.clas.ufl.edu/hager/papers/Lightning/EsondeNov2008/ChargeTransport.pdf
http://www.atmo.arizona.edu/students/courselinks/fall14/atmo336/lectures/sec2/lightning.html