### Bachelor's honours thesis abstract

B.Sc. (Hons.) in Earth Sciences (Geophysics) at Memorial University of Newfoundland (MUN), granted
May 1985, with a thesis on "Geomagnetic Core-Mantle Coupling and the Associated Decade Fluctuations
in the Length of the Day."
This paper extends the work of Rochester (1960) and Roden (1963) on
electromagnetic coupling and its effects on length of day (lod)
variations to include the effects of continuously varying mantle
conductivity. Using the torque formulation of Stix (1982) and
the Backus (1983) conductivity profile, an equilibrium torque
Gamma-acc of 6 x 10^18 N-m and a perturbing time constant tau-c
of 4 years are obtained. The tightness of coupling is increased
by a factor of 7 over Rochester's model and a factor of 2.5 over
Roden's best model. Perturbation torques amounting to 10-15% of
the equilibrium torques now satisfactorily account for the largest
changes in the lod of 3 ms/decade. This level of variability is
likely since as mantle conductivity is concentrated towards the
CMB (core-mantle boundary), higher harmonics become increasingly
important, as is manifested in increasing low order truncation
error in torque calculations. Detailed quantitative modelling must
await further extension of time series and developments in measurement
techniques and theory.