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Generation of a strong magnetic field using uniform heat flux at the surface of the core

Nature Geoscience volume 2, pages 802–805 (2009)Cite this article

Abstract

The Earth’s main magnetic field is thought to be generated by motions in the planet’s fluid outer core, which lead to an effect similar to that of a dynamo1,2,3. Recent high-resolution numerical simulations produce only a non-dipolar4 or a dipolar but comparatively weak magnetic field5,6 unlike that of the Earth. Older models that did generate a strong, Earth-like field needed to use unrealistically high viscosities for the core fluid7,8,9,10. Common to most of the models is the assumption of a laterally uniform core-surface temperature. Here we use a low-viscosity geodynamo model to evaluate the effect of a different and more realistic boundary condition—a uniform heat flux at the surface of the core—on the simulation of an Earth-like magnetic field. Our results show that when the surface temperature is laterally uniform, only a weak magnetic field is generated because planetary-scale fluid circulations are suppressed. In contrast, a laterally uniform heat flux at the core’s surface leads to large-scale convective flows, and a comparatively strong dipole-type magnetic field. Contrary to previous work11,12, we suggest that thermal conditions at the core surface have a strong effect on low-viscosity geodynamo models.

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Figure 1: Snapshots of velocity and magnetic field.
Figure 2: Time-averaged structures of velocity and magnetic field.

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Acknowledgements

Numerical simulations were carried out at the Earth Simulator Center, Yokohama, Japan. A.S. was supported by a grant-in-aid from Yamada Science Foundation. P.H.R. thanks NSF for partial support.

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Authors and Affiliations

  1. Department of Earth and Planetary Science, School of Science, University of Tokyo, Tokyo 113–0033, Japan

    Ataru Sakuraba

  2. Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California 90095, USA

    Paul H. Roberts

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  1. Ataru Sakuraba
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  2. Paul H. Roberts
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Contributions

A.S. constructed the model, carried out numerical analyses and prepared the manuscript. P.H.R. helped with the model and the manuscript.

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Correspondence to Ataru Sakuraba.

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Sakuraba, A., Roberts, P. Generation of a strong magnetic field using uniform heat flux at the surface of the core. Nature Geosci 2, 802–805 (2009). https://doi.org/10.1038/ngeo643

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