Title: Magnetic shielding properties of the Earth's mantle
Abstract: Estimates of the true geomagnetic spectrum are obtained over a period range of 40 days to 22 years. From various lines of evidence it is deduced that any magnetic signals generated inside the core and introduced at the core-mantle boundary with periods less than approximately 4 years are effectively cut off from observation by the conducting lower mantle. Under simplifying assumptions, the transfer function for a two-layer model of the mantle is obtained, whose absolute value, with geometrical attenuation removed, yields the physical attenuation. By independently varying the mean conductivity and thickness (c - b) of the lower mantle, as well as relating them by , the magnetic shielding properties of the mantle as a function of period are investigated in detail. When one normalizes the conductivity distribution by τ = constant, attenuation is insensitive to large changes in the distribution. A 20% decrease in maximum lower mantle thickness (2000 km) has no appreciable effect on mantle shielding properties; attenuation is primarily determined by the factor . For emu and periods less than 20–40 years, mantle attenuation becomes increasingly nonlinear, and small changes in affect mantle attenuation more strongly than changes in harmonic degree n. It is concluded that refined estimates of lower mantle conductivity are not likely to come from studies based on the mantle's shielding properties.
Publication Year: 1967
Publication Date: 1967-05-15
Language: en
Type: article
Indexed In: ['crossref']
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Cited By Count: 47
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