Ba. Buffett et De. Goertz, MAGNETIC DAMPING OF THE TRANSLATIONAL OSCILLATIONS OF THE INNER-CORE, Geophysical journal international, 120(1), 1995, pp. 103-110
We calculate the magnetic perturbation that occurs near the inner core
boundary when the conducting materials on either side of the boundary
are displaced by translational oscillations of the inner core. The as
sociated Lorentz forces and ohmic losses cause changes in the period a
nd damping of the oscillations which may be detectable in gravity meas
urements. Estimates of these changes depend on the average value of th
e radial main field BBAR(r) near the inner core boundary. The value of
BBAR(r) also affets the character of the magnetic disturbance in the
fluid core. For BBAR(r) < 0.002 T, the magnetic perturbation at the in
ner core boundary propagates into the overlying fluid core by diffusio
n, while for BBAR(r)> 0.002 T the perturbation is transmitted by Alfve
n waves. The most observable effects are associated with the damping o
f the oscillations. Typical values of the damping factor Q vary widely
with BBAR(r), but may be as low as 2000. Since Q is extremely sensiti
ve to the main magnetic field we suggest that observations of the inne
r core oscillations might be used to infer the average strength of the
field near the inner core boundary. To facilitate the interpretation
of the gravity measurements, we present analytical expressions for the
effect of a magnetic field on the period and Q of inner core oscillat
ions.