上端応力無し,下端滑り無し条件を課した回転球殻中に出現する弱磁場ダイナモ(宇宙・惑星(3),一般講演)

概要

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Numerical experiments of MHD dynamo in a rotating spherical shell with stress-free top and no-slip bottom boundaries are performed. The Ekman number, the Prandtl number, and the ratio of inner and outer radii are fixed to 10^<-3>, 1, and 0.35, respectively. The magnetic Prandtl number is varied from 5 to 50, and the modified Rayleigh number is increased from 1.5 to 10 times critical. All the obtained successful solutions are weak field-dynamo, that is, the total magnetic energy is far less than the total kinetic energy. These solutions are characterized by the two-layer spatial structure. The upper layer is governed by prograde strong zonal flows and less-organized prograde propagating spiral convection vortices, while the lower layer is dominated by turbulent retrograde propagating columnar convection vortices. The strong zonal flow in the upper layer prevents the magnetic field generated in the lower layer from penetrating to the outer surface.
2010-09-09