The magnetic field of the Earth is generated by convection in the liquid
core and energy necessary for this process comes from the cooling of the
core which provide several buoyancy sources. The Energy balance shows that
the heat flow at the CMB is equilibrated by the sum of four energy sources:
secular cooling, latent heat offreezing at the ICB,compositional energy
due to the redistribution of light elements upon freezing and, perhaps,
radiogenic heating. The entropy balance can be used to show that the compositional
energy is most effectively transformed into ohmic dissipation. All these
energy sources, save the radioactivity, are a function of the radius of
the inner core and are proportional to its growth rate. This growth rate
can be computed for any given ohmic dissipation in the core, and this allows
the computation of the heat flow across the CMB. Alternatively, if the
heat flow at the CMB is known, the growth rate of the inner core can be
computed, giving the ohmic dissipation in the core. Unfortunately, neither
the ohmic dissipation nor the heat flow at the CMB is known with precision.
Additional uncertainties come from the imperfectly density difference of
chemical origin between the inner and outer cores. Nevertheless, exploration
of a reasonable parameter space, show that the inner core likely no older
than 2 Ga, and that the magnetic field prior to that time was sustained
by thermal convection alone.
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主催：愛媛大学地球深部ダイナミクス研究センター