Viscosity Near Earth's Solid Inner Core

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Science  16 Apr 1999:
Vol. 284, Issue 5413, pp. 461-463
DOI: 10.1126/science.284.5413.461

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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.

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