Ground is no longer at ground potential

I MEGO on a lot of the optics in Phil's book (entendues and such) but the photon budget stuff is comprehensible, and there's some really good stuff about electronic design.

It's roughly half electronics, which makes sense since the world is half electronics.

Yes, if you know about the theorem about combing a hairy ball the whole thing seems less convincing!

Mike.

Now that it is already April 2nd, some serious comments might be appropriate :-) Depending on sources, those figures vary quite a lot. While this link talks about top layer at 50 km (so below ionosphere), in practice, it appears that the top layer are at about 100 km, i.e in the ionosphere E-layer.

The current from a single storm cell to the ionosphere is on average about 1 A, so no wonder that sprites are observed above thunder clouds, which extends to about 100 km, conforming the top layer height.

Thus the current from the ground under the storm cell (1 A) to the ionosphere and then back down as clear air leakage (about 2-10 pA/square meter depending on source) down to the ground will complete the circuit. Thus, due to ground currents from the surrounding to under the storm cell will cause some ground potential differences.

This is not much of practical concern compared to solar storms, in which huge potential differences are created in the ground and quite huge currents may flow in the ground, with still large potential differences between sites. If there are a good conductor between two sites (such as a gas pipeline grounded at both ends). the majority of this ground current flows through he pipeline, causing electrochemical problems.

So in reality, any two locations is going to have a different ground potential and there is no such thing as a universal ground potential.

You can stick a pair of rods into the ground some distance apart, and measure/listen to the voltage gradient.