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A jet-like structure revealed by a numerical simulation of rotating spherical-shell magnetoconvection

Published online by Cambridge University Press:  05 February 2007

ATARU SAKURABA
ATARU SAKURABA*
Affiliation:
Department of Earth and Planetary Science, University of Tokyo, Tokyo, Japan
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Abstract

Numerical results on thermally driven nonlinear magnetoconvection in a rapidly rotating fluid spherical shell are reported. A uniform magnetic field that is parallel to the rotation axis is imposed externally. The Ekman number is 2 × 10−6, representing a state of negligible viscosity, as in the Earth's core. The convection pattern is characterized by a few large-scale vortex columns superimposed on a fast westward (retrograde) zonal flow. In the equatorial region, an anticyclonic vortex is intensified, in which an induced axial magnetic field is stored. Interaction between the magnetized vortex and the zonal flow leads to a thin jet at the western side of the vortex. The jet is also characterized by a thin electric current sheet caused by a steep gradient of the axial magnetic field. Because of this structure, the jet region can be designated as a magnetic front by analogy with fronts in mid-latitude atmospheric cyclones. It can be estimated from an order-of-magnitude analysis that the jet width decreases in inverse proportion to the zonal flow speed, and that the jet speed and the sheet-like electric current are proportional to the square of the zonal flow speed.

Type
Papers
Information
Journal of Fluid Mechanics , Volume 573 , February 2007 , pp. 89 - 104
Copyright
Copyright © Cambridge University Press 2007

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