TY - JOUR
T1 - Effects of boundary layers on magnetic field behavior in an MHD dynamo model
AU - Takahashi, F.
AU - Katayama, J. S.
AU - Matsushima, M.
AU - Honkura, Y.
N1 - Funding Information:
This work was partially supported by the Japan Society for the Promotion of Science, under the grant-in aid for scientific research nos. 10640404 and 11640412. This work was also partially supported by the “Earth Simulator” project of the Ministry of Education, Cuture, Sports, Science and Technology, Japan. The computations were performed on computers powered by Alpha 21164 and Alpha 21264 at the Honkura Laboratory, Tokyo Institute of Technology, and on SGI Origin2000 at the Computer Center, Tokyo Institute of Technology.
PY - 2001
Y1 - 2001
N2 - Numerical simulations of three-dimensional self-consistent MHD dynamos in a rotating spherical shell are performed to examine the structures of the velocity and the magnetic fields and the mechanism of magnetic field generation. Emphasis is put on an important role of the boundary layer which arises for the no-slip boundary condition. The most important is precise computation in the boundary layers, in which the number of grid points must be large enough to ensure spatial resolution there. The result of computation shows that the dipole field is dominant and that the magnetic field is concentrated in the convection columns. Such results are the same as those derived from our previous study for the stress-free boundary condition. A marked difference is the strong toroidal magnetic field generated by strong shear flow inside the boundary layers. Also the effect of magnetic diffusion is strong and more significant than that of magnetic induction near the spherical surfaces. This suggests that the so-called frozen-flux hypothesis, which has usually been used to estimate core surface flows, does not necessarily hold for the cases in which significant boundary layers appear.
AB - Numerical simulations of three-dimensional self-consistent MHD dynamos in a rotating spherical shell are performed to examine the structures of the velocity and the magnetic fields and the mechanism of magnetic field generation. Emphasis is put on an important role of the boundary layer which arises for the no-slip boundary condition. The most important is precise computation in the boundary layers, in which the number of grid points must be large enough to ensure spatial resolution there. The result of computation shows that the dipole field is dominant and that the magnetic field is concentrated in the convection columns. Such results are the same as those derived from our previous study for the stress-free boundary condition. A marked difference is the strong toroidal magnetic field generated by strong shear flow inside the boundary layers. Also the effect of magnetic diffusion is strong and more significant than that of magnetic induction near the spherical surfaces. This suggests that the so-called frozen-flux hypothesis, which has usually been used to estimate core surface flows, does not necessarily hold for the cases in which significant boundary layers appear.
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U2 - 10.1016/S0031-9201(01)00283-7
DO - 10.1016/S0031-9201(01)00283-7
M3 - Article
AN - SCOPUS:0035688107
SN - 0031-9201
VL - 128
SP - 149
EP - 161
JO - Physics of the Earth and Planetary Interiors
JF - Physics of the Earth and Planetary Interiors
IS - 1-4
ER -