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    Re: Auroras/compass readings
    From: Charles Seitz
    Date: 2004 Oct 17, 21:43 -0400

    This is what the geophysicists at NOAA have to
    5e. What influences the magnetic field measured by my compass?
    The Earth's magnetic field is actually a composite of several magnetic
    fields generated by a variety of sources. These fields are superimposed
    on each other and through inductive processes interact with each other.
    The most important of these geomagnetic sources are:
         a. the Earth's conducting, fluid outer core (~90%);
         b. magnetized rocks in Earth's crust
         c. fields generated outside Earth by electric currents flowing in
    the ionosphere and magnetosphere
         d. electric currents flowing in the Earth's crust (usually induced
    by varying external magnetic fields)
         e. ocean current effects
    These contributions all vary with time on scales ranging from
    milliseconds (micropulsations) to millions of years (magnetic
    reversals). More than 90% of the geomagnetic field is generated by the
    Earth's outer core. It is this portion of the geomagnetic field that is
    represented by the Magnetic Field Models.
                                     ---  CHAS

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