Letter

Nature 454, 1106-1109 (28 August 2008) | doi:10.1038/nature07227; Received 2 May 2008; Accepted 27 June 2008

Formation of current coils in geodynamo simulations

Akira Kageyama1, Takehiro Miyagoshi1 & Tetsuya Sato1

  1. Earth Simulator Center, Japan Agency for Marine-Earth Science and Technology, Yokohama, 236-0001, Japan

Correspondence to: Akira Kageyama1 Correspondence and requests for materials should be addressed to A.K. (Email: kage@jamstec.go.jp).

Computer simulations have been playing an important role in the development of our understanding of the geodynamo1, 2, 3, but direct numerical simulation of the geodynamo with a realistic parameter regime is still beyond the power of today's supercomputers. Difficulties in simulating the geodynamo arise from the extreme conditions of the core, which are characterized by very large or very small values of the non-dimensional parameters of the system. Among them, the Ekman number, E, has been adopted as a barometer of the distance of simulations from real core conditions, in which E is of the order of 10-15. Following the initial computer simulations of the geodynamo4, 5, the Ekman number achieved has been steadily decreasing, with recent geodynamo simulations6, 7, 8 performed with E of the order of 10-6. Here we present a geodynamo simulation with an Ekman number of the order of 10-7—the highest-resolution simulation yet achieved, making use of 4,096 processors of the Earth Simulator. We have found that both the convection flow and magnetic field structures are qualitatively different from those found in larger-Ekman-number dynamos. The convection takes the form of sheet plumes or radial sheet jets9, rather than the columnar cell structures10 that are usually found. We have found that this sheet plume convection is an effective dynamo and the generated current is organized as a set of coils in the shape of helical springs or at times as a torus.

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