I understand that. You didn't respond to the other questions I raised. I don't know whether you're specifically ignoring them, or not.
As I already said, two-fluid (dealing with actual motions of positive and negative charges) or Hall MHD (which slices out magnetic reconnection ["field line breaking"]) both sounded pretty close to what I'd expect of dealing with electrodynamics. If you say that MHD does deal with currents, I say fine (especially in the two cases above, which sound like they may remedy the deficiencies Alfvén pointed out "way back"; IE dealing with the "particle" model rather than the "fluid" model).
In any event, in discussion of the topic with people on various forums (often with learned folks like yourself), I've asked whether currents can flow in space and whether specific formations could be a manifestation of that. The general answer is usually "currents can't flow in space," or "charge can't be separated in space, thus currents can't flow in space," etc. I believe that's not correct.
Do you think that currents can flow in space (over large distances)? If so, do you think that they may be responsible for some of the energetic processes (various synchrotron radiation sources) we see and/or specific structures? If not, why not? If not, how does one explain the ubiquitous magnetic fields that ARE seen in space? There aren't a bunch of permanent ferromagnets floating about...
Again, taking as an example a magnetic field circling a long rope-like stream of plasma (or even a twisted pair of long rope-like streams of plasma). Is it conceivable that the plasma is moving in such a way as to constitute a current that is responsible for the magnetic field? Much like the filaments in your typical plasma globe...
For instance, the "flux ropes" discovered by THEMIS in Dec 2007. I assume you'd agree they constitute currents (field-aligned currents, or Birkeland currents) flowing through the interplanetary plasma? Pretty non-controversial.
(NASA Spacecraft Make New Discoveries About Northern Lights)
http://www.nasa.gov/mission_pages/themis/auroras/northern_lights.html
"The satellites have found evidence of magnetic ropes connecting Earth's upper atmosphere directly to the sun," said David Sibeck, project scientist for the mission at NASA's Goddard Space Flight Center, Greenbelt, Md. "We believe that solar wind particles flow in along these ropes, providing energy for geomagnetic storms and auroras."
A magnetic rope is a twisted bundle of magnetic fields organized much like the twisted hemp of a mariner's rope.
Why is it, do you think, that they call them "magnetic ropes" rather than "electric currents?" And why not credit Birkeland's prediction from the early 1900's (as was already done for Triad's discovery of "Birkeland currents" in 1973)? Just out of curiosity. Are they just dumbing it down for the public?
They quite off-handedly mention an occasional "burst of electrical current within the solar wind," but still talk in terms of "magnetic ropes." That seems a bit odd to me. Would it kill them to say "we observed an electric current, and it did something interesting, though we're still trying to pin down exactly what"?
A later THEMIS article again talks in terms of the magnetic fields themselves "doing things."
(THEMIS Satellites Discover What Triggers Eruptions of the Northern Lights)
http://www.nasa.gov/mission_pages/themis/auroras/themis_power.html
This pattern consists of a period of reconnection, followed by rapid auroral brightening and rapid expansion of the aurora toward the poles. This culminates in a redistribution of the electrical currents flowing in space around Earth.
It's nice that they talk about electric currents, but they seem to talk about only the after-effect changes, as a result of the changing magnetic field line topology "doing something." Is not the magnetic field topology change the result of a change in an underlying current system? Be it a current sheet, double layer, filament (several filaments twined together), etc?
Again, getting back to the simplest case current-in-wire analogy: if you remove the current from the wire (except in the case of permanent magnets), the magnetic field collapses. This seems to me to make the action of current(s) the thing to follow, rather than the magnetic field (which seems to be a product of the net motion of the charged particles). If there's an interesting magnetic field topology change, what's the change to underlying currents that caused it (that's how I'd frame the question anyway)? What's the electrical structure that gives rise to the magnetic structure?
Is not a change in the electric current that which causes the auroral brightening (a more excited "glow mode" discharge in plasma) AND moreover the magnetic field topology change? Be it a rapidly discharging double layer or some other process...
Regards,
~Michael Gmirkin