novice questions about the Earth's electric field...

[SRH]

Does the Earth's electric field extend beyond the ionosphere, or does it just stop there?

If it does extend beyond, in which direction does it point (towards the Earth or away from the Earth)?
And just to make sure that I understand correctly, would an electron in space (above the ionosphere) move towards the Earth or away from the Earth?

Thank you very much.

[tusenfem]

If you are talking about the "fair weather electric field" then this a field like a capacitor. From Mission Instruments site

On a clear day, when the atmosphere is clear of storm clouds, the primary source of electric charge creating an electric field on the surface of the earth is the ionosphere. This can be thought of as a large dome-shaped electrode high above the earth, which produces positive charges which contrast to the relatively negatively charged earth. This scenario creates what is termed a "fair weather" electric field due to the positive charge overhead. When this "fair" field is measured by the EFS 1001 field mill, it can be seen to produce an output of from 50 to about 200 Volts per meter ("V/m"). This value varies, depending upon conditions in the atmosphere, and is also altered by "local effects". Such effects are caused by anything which can carry electrical charge, including but not limited to atmospheric space charge, dust, smoke, litter, etc. Usually, though, the field stays between -50 and -200 V/m during fair or non-stormy weather.

As the total charge content overall is zero, there will be no field outside the ionosphere (theoretically in ideal situation), naturally there will be some "leaking" of the field.

[grapes]

Which means your head is a few hundred volts higher than your feet. :)

That doesn't cause a problem, because there's relatively little charge available. However, if you mount a large metal object up in the air, insulated from the ground, it can over time build up enough charge to ... do serious damage.

[ShinAce]

it can over time build up enough charge to ... do serious damage.

Like those unfortunate enough to learn the hard when flying in a kite in a sandstorm.

Basically, the earth turns into a concentric shell capacitor. A fancy name for a ball inside a ball with the electric field being in the gap between them. Interestingly, the electric field is zero outside of this capacitor. The electric field exists 100% in the gap. Which is to say, charges in space should feel no tug as a result of earth's electric field. Whether the earth has a residual electric charge or not is beyond me, but I've been led to believe it is electrically neutral. This also means that a charged capacitor has no effect on electrons outside of it. Likewise, a coaxial cable uses a grounded shell to 'neutralize' the electric field within it.

Now, earth's magnetic field is a different story.

[SRH]

Is "no E field above the ionisphere" just a theory, or has it been experimentally verified?

Given that an E field is perpendicular to the Magnetic field, wouldn't this mean that if the Earth's Mag field extends beyond the ionosphere, then the Earth's E field must as well?

Thanks.

[ShinAce]

A geostationary satellite with a space tether might be able to make conclusive measurements. http://en.wikipedia.org/wiki/Electrodynamic_tether . Notice the generator takes advantage of magnetic fields and speed.

If the earth had even a small charge, say, one extra electron for every million atoms, we would notice the currents between us and positively charged bodies. The residual charge on the earth as a result of interacting with things like the solar wind and cosmic wind is tiny. I was shocked at how terrible of a current reservoir the earth is. Even though we use the soil as a conductor in circuits, it has a relatively small number of mobile electrons. If doing this could deplete them, no grounded circuit would last long.

[quotation]

Is "no E field above the ionisphere" just a theory, or has it been experimentally verified?

I recently read one paper where they utilized six different devices to measure the effects of the solar wind on the magnetosphere. They noted periodic "erosion" of the magneotsphere, which put it in occasional close proximity to ionospheric currents, from whence one could deduce some leakage (as noted above), but which I think would quickly be accomodated by the magnetosphere, so I'd say, yeah, it's been experimentally verified.

[korjik]

Is "no E field above the ionisphere" just a theory, or has it been experimentally verified?

Given that an E field is perpendicular to the Magnetic field, wouldn't this mean that if the Earth's Mag field extends beyond the ionosphere, then the Earth's E field must as well?

Thanks.

Electric and magnetic fields are perpendicular to one another in an electromagnetic wave in space. When talking about other fields, there is no requirement that they be perpendicular.

You can also have one field without the other, and you can have both and they have nothing to do with one another. The last case is what applies in the Earth's atmosphere.

[ShinAce]

The earth, being a good conductor, would have charge evenly distributed on the surface. This would give an E field pointing radially from the center. In other words, an electric compass would point straight up at every point on the surface. Definitely not the same as the magnetic field, which points from one spot on earth to another. The magnetic field is axially symmetric, while an electric field would be radially symmetric. Keep in mind the magnetic field can do weird things, while the electric field would always have the same shape. This is ignoring things like lightning, since currents mess up your electric field mojo.

edit: I was just wondering if rocks could record lightning strikes, and it appears they can: http://www.archaeophysics.com/pubs/LIRM.html

Which is to say, if you know how that rock behaves to a certain current, you could deduce the intensity of the lightning strike. In other words, you could try to map some of the earth's electric fields. It's out there, but if you're lucky, you might even trace which direction the current passed.