Re: Earth's Magnetic Field

[William Beaty <billb@ESKIMO.COM>]

On Sun, 11 Jul 1999, K. Lee Lerner wrote:

> Dear Fellow Scholars & Colleagues,
>
> Perhaps the geomagnetic field is best understood in terms of a self-exciting
> dynamo model?  Topological differences (e.g., the hole), however,  and
> symmetry considerations render it unlikely that the geodynamo is like a
> self-exciting disk dynamo.

Here's a thought-experiment of mine from years ago:

  http://www.amasci.com/freenrg/chevron.gif

I never tried building this one.  It's a self-excited cylindrical
homopolar motor/generator based on the spiral-slots technique used in
self-exciting disk HPGs. It would create a tripolar field rather than the
dipole field associated with disk-shaped generators.  Its flux lines would
be directed radially outwards through the surface of the slotted cylinder.
Cylindrical HPGs have been built, although they do suffer from having
*two* high-speed brushes rather than the disks which have just one
high-speed, high-wear brush at the rim and a second, low-speed brush near
the axis.

In the earth's core, swirling metal might act more like rotating cylinders
than like spinning disks.  It's easier to imagine the electrical contacts
between rotating cylindrical fluid regions (if the Earth's core acts like
an array of spinning disks, how do the "sliding brushes" make contact with
the centers of those disks?  Cylinders make more sense.)  In any case, if
we take a small segment from a disk-type or cylinder-type HPG machine,
then imagine that the Earth's liquid core is composed of an interconnected
array of these moving segments, we can imagine how the swirling iron could
spontaneously generate b-fields and electric current.  There would be no
disks or cylinders as such, but there would be iron "parts" in relative
motion with other iron "parts", with sliding conductive contact between
them and with b-fields extending through their surfaces.


> Regardless, magnetohydrodynamic calculations are exceeding difficult.   A
> fair start on this topic  can be obtained from a review of C.M.R. Fowler's
> excellent text -- The Solid Earth (University of Cambridge Press,
> ISBN0-521-38590-3).

I imagine that the problem would be vaguely similar to the problem of
writing equations for turbulent fluid flow.  Computer simulation would
make inroads, and that was the technique used by the authors of that SciAm
article.  I recall that they mentioned controversy over this.  Some
researchers don't trust that computer simulations aren't introducing major
artifacts.  Also, there was need to "tune" the simulations to bring them
in line with known behaviors of the Earth's core.  If the actual
characteristics of the Earth's core are unknown, then I can see why such
tuning would be necessary.


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William J. Beaty                                  SCIENCE HOBBYIST website
billb@eskimo.com                                  http://www.amasci.com
EE/programmer/sci-exhibits          science projects, tesla, weird science
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