Re: Earth's Magnetic Field

[brian whatcott <inet@INTELLISYS.NET>]

At 15:38 7/9/99 -0400, you wrote:
> I am looking for information about the origin of
> the earth's magnetic field;
> i.e. what causes it.
>
> Anyone have a good explanation / resource?
>
> TIA,
> bob yeend

Without further research we can call up at least these data
from our general knowledge:
There is iron in the core.
There is conductive fluid material in the core.
There is rotating motion available, and so we can suppose that
the motion of the solid and fluid components in the core are not
necessarily synchronized.
 We can expect that relative movement between a conductor and even
a very small remanent magnetic field from an iron-bearing material
can give rise to a circulating current which opposes that relative
 movement.
That current would increase the size of the magnetic field.

 We can reasonably suppose that the masses and forces involved are huge.
It would not be unreasonable to suppose that the restitutional momentum
mentioned above can provide a mechanism for reversing the field.

We evidently cannot model the effect as a simple oscillation - because
the stratigraphic record shows widely varying intervals of polarity
reversal, and so we arrive at a model that shows non-linear activity -
it may be chaotic - which should be unsurprising; outside the
imaginations of engineers & physicists a vast array of natural
phenomena are non-linear.

Well, that represents quite enough speculation - in fact, far too much,
so it's time to consult some writers who have considered the matter.

Gilbert (in expounding his theory that magnetic variation is due
to the distribution of mountainous asperities which pull the direction
aside from the geographic pole) says this:
"...along the coasts of Spain, France, England, Holland, Germany,
Denmark, Norway, the land on the right and to the east is all
continent...[] on the left, immense seas now we should expect that
[]  magnetic bodies would deflect a little eastward...
[]  Very different is the case on the east coasts of North America for
from the region of Florida through Virginia and Norumbega to Cape Race
and away to the north, the needle turns to the west."

De Magnete... Gilbert 1600

(Examination of declination at the east coast of Greenland would have
 provided a counter example.)

One hundred twenty two years later, G. Graham was examining a compass
needle under a microscope. He noticed changes lasting from less than
a second, to several days. These diurnal and irregular pulsations are
attributed (in part) to atmospheric carriage of charged particles through
 the Earth's field in the E region of the ionosphere at around 100 km
altitude.

Greenwich Observatory on the Thames, was recording changes of declination
 and inclination from 1580 onwards.
 These data plot to an ellipse which to date is three quarters complete.
Inclination 66 to 74 degrees; declination 25 West to 10 East.

When I close by mentioning that the currents thought to be responsible
for the geomagnetic field exist below 2900 km and demand a rather large
 value of resistivity around one ohm-meter, then my survey is almost
complete.
   I should mention that in recent years a model of the geomagnetic
generator has been demonstrated which shows plausible properties.




brian whatcott <inet@intellisys.net>
Altus OK