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Science 16 April 1999:
Vol. 284. no. 5413, pp. 461 - 463
DOI: 10.1126/science.284.5413.461
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Reports

Viscosity Near Earth's Solid Inner Core

D. E. Smylie

Anomalous splitting of the two equatorial translational modes of oscillation of Earth's solid inner core is used to estimate the effective viscosity just outside its boundary. Superconducting gravimeter observations give periods of 3.5822 ± 0.0012 (retrograde) and 4.0150 ± 0.0010 (prograde) hours. With the use of Ekman layer theory to estimate viscous drag forces, an inferred single viscosity of 1.22 × 1011 Pascal seconds gives calculated periods of 3.5839 and 4.0167 hours for the two modes, close to the observed values. The large effective viscosity is consistent with a fluid, solid-liquid mixture surrounding the inner core associated with the "compositional convection" that drives Earth's geodynamo.

Department of Earth and Atmospheric Science, York University, Toronto, Ontario M3J 1P3, Canada.

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Science. ISSN 0036-8075 (print), 1095-9203 (online)