Geomagnetic Westward Drift and Irregularities in the Earth's Rotation

Details Geomagnetic Westward Drift and Irregularities in the Earth's Rotation Geomagnetic Westward Drift and Irregularities in the Earth's Rotation

May 1960

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1960rspta.252..531r&link_type=abstract

Philosophical Transactions for the Royal Society of London. Series A, Mathematical and Physical Sciences, Volume 252, Issue 1018

Physics

47

Scientific paper

Bullard et al.'s (1950) rigid-sphere model for the steady westward drift of the earth's non-dipole magnetic field is extended to include the magnetic coupling provided by the presence of the higher multipole fields at the core-mantle boundary. If the first six harmonics of the observed surface field are taken into account, the retarding couple on the mantle is increased by a factor of 1\cdot 6. Using this result it would follow from Bullard's specialized model of the core that the geomagnetic dynamo mechanism generates a toroidal field of several hundred gauss in the deep interior of the core. Time-dependent perturbations of the mantle-core coupling are investigated rigorously, and it is shown that reasonable fluctuations of the fields at the core-mantle boundary are capable of explaining changes in the length of day at the rate of order 1 ms in 10 yr. The tightness of the coupling is increased by 60% over that afforded by Bullard's model. The argument provides additional evidence that the mean electrical conductivity in the bottom 2000 km of the mantle is at least 10-9 e.m.u. A summary of knowledge of the distribution of electrical conductivity with depth in the earth is given in the Introduction.

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