期刊
GEOPHYSICAL JOURNAL INTERNATIONAL
卷 196, 期 2, 页码 724-735出版社
OXFORD UNIV PRESS
DOI: 10.1093/gji/ggt432
关键词
Earth rotation variations; Dynamo: theories and simulations; Rapid time variations
资金
- Natural Environment Research Council [NE/I012052/1]
- NERC [NE/I012052/1] Funding Source: UKRI
- STFC [ST/I00162X/1, ST/K00042X/1, ST/H008802/1] Funding Source: UKRI
- Natural Environment Research Council [NE/I012052/1] Funding Source: researchfish
- Science and Technology Facilities Council [ST/K00042X/1, ST/H008802/1, ST/I00162X/1] Funding Source: researchfish
The predominant force balance in rapidly rotating planetary cores is between Coriolis, pressure, buoyancy and Lorentz forces. This magnetostrophic balance leads to a Taylor state where the spatially averaged azimuthal Lorentz force is compelled to vanish on cylinders aligned with the rotation axis. Any deviation from this state leads to a torsional oscillation, signatures of which have been observed in the Earth's secular variation and are thought to influence length of day variations via angular momentum conservation. In order to investigate the dynamics of torsional oscillations (TOs), we perform several 3-D dynamo simulations in a spherical shell. We find TOs, identified by their propagation at the correct Alfven speed, in many of our simulations. We find that the frequency, location and direction of propagation of the waves are influenced by the choice of parameters. Torsional waves are observed within the tangent cylinder and also have the ability to pass through it. Several of our simulations display waves with core traveltimes of 4-6 yr. We calculate the driving terms for these waves and find that both the Reynolds force and ageostrophic convection acting through the Lorentz force are important in driving TOs.
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