Scale variability in convection-driven MHD dynamos at low Ekman number

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• 作者：Futoshi Takahashi ; Masaki Matsushima ; Yoshimori Honkura
• 关键词：Dynamo ; Core ; Ekman number ; Scale separation
• 刊名：Physics of the Earth and Planetary Interiors
• 出版年：2008
• 期刊代码：73_00319201
• 类别：ear
• 出版时间：April 2008
• 卷：167
• 期：3-4
• 页码：168-178
• 文件大小：2454 K

摘要

We have undertaken a numerical study of convection-driven MHD dynamos in a rapidly rotating spherical shell with the Ekman number, E, down to 2×10⁻⁶ and the magnetic Prandtl number, Pm, down to 0.2. We focus on the characteristic scales of the flow and the magnetic field. Smaller-scale convection vortices responsible for generating the magnetic field appear at lower Ekman numbers, while the scale of the magnetic field shows less variation compared with the flow. As a result, scale separation between the flow and the magnetic field occurs as the Ekman number is decreased. Scale separation helps dynamos to maintain the magnetic field at Pm<1 through increase in the effective value of the magnetic Reynolds number.