HR: 0800h
AN: S41C-1027    [Abstracts]
TI: Rayleigh-Benard Convection in Spherical Shell with Infinite Prandtl Number at High Rayleigh Number
AU: * Yamagishi, Y
EM: yamagisi@jamstec.go.jp
AF: IFREE, JAMSTEC, 2-15 Natsuhima-cho, Yokosuka, 237-0061 Japan
AU: Yanagisawa, T
EM: yanagi@jamstec.go.jp
AF: IFREE, JAMSTEC, 2-15 Natsuhima-cho, Yokosuka, 237-0061 Japan
AU: Hamano, Y
EM: hamano@eps.s.u-tokyo.ac.jp
AF: Dept. of Earth and Planet. Sci., Univ. of Tokyo, 7-3-1 Bunkyo Hongo, Tokyo, 113-0033 Japan
AB: Convective motion in the mantle promotes structural and thermal evolutions of the Earth. Its understanding is based on simple Rayleigh-B__'{e}nard (RB) convection although the Earth's mantle convection is affected by many factors such as internal heating, strong temperature dependence of viscosity, yield strength of the materials and the phase transitions. So far, many researches have been directed towards understanding physics of simple RB convection. However the accurate numerical simulations of RB convection in spherical shell geometry with infinite Prandtl number (Pr) at high Rayleigh number (Ra) like the Earth's mantle (Ra around 10⁷ at present and more for the ancient Earth) is few because of limited computational resources. Here we have investigated systematically simple RB convection in the spherical shell geometry with infinite Pr and a wide Ra range by using a supercomputing system, the Earth Simulator (JAMSTEC), and succeeded in calculating the thermal convection with Ra up to 10⁸. In order to understand the most basic features of the high Ra and Pr convection, the viscosity is assumed to be constant and other complexities of the mantle are not considered here. For all Ra, the convection pattern is illustrated as follows; the sheet-shaped downwelling and upwelling flows originate from the boundary layers and concentrate gradually into cylindrical flows. We have examined the relationship between Ra and the Nusselt number (Nu), and obtained that Nu is proportional to Ra^0.30. The power found in our study is larger than that of the previous studies. We also tried to quantify the convection pattern by the power spectrum of the temperature field at each depth in terms of spherical harmonic degrees. This analysis revealed that the structural scale of convection is different between the boundary region and the isothermal core region. The former is characterized by the cell type structure constructed by the sheet-shaped downwelling and upwelling flows, and the latter by the plume type structure which consists of the cylindrical flows.
DE: 8125 Evolution of the Earth (0325)
DE: 8147 Planetary interiors (5430, 5724, 6024)
SC: Seismology [S]
MN: Fall Meeting 2005