回転球殻MHDダイナモ解に対する上部力学的境界条件の影響(環境・地球・宇宙宇宙・惑星(1),一般講演)

概要

論文の詳細を見る
Numerical experiments of magnetohydrodynamic (MHD) dynamos driven by thermal convection in a rotating spherical shell with a free-slip top boundary and a no-slip bottom boundary 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 Pm is varied from 1 to 50. The modified Rayleigh number Ra is increased up to 15 times the critical value Ra_c. MHD calculations are carried out from non-magnetic thermal convection solutions with a weak dipole magnetic field on top of them, and dynamo solutions are obtained when Ra≥1.87Ra_c and Pm≥4. The strong prograde zonal flows in the non-magnetic solutions disappear in the dynamo solutions as the evolution of magnetic fields, and slow retrograde zonal flows emerge at the top of the spherical shell. As a result, the omega effect which was expected from the strong zonal flows of the non-magnetic solutions does not operate effectively. All of the obtained dynamo solutions are considered to be categorized as the α^2-type dynamo.
2009-09-02