| Nonlinear free thermal convection in a spherical shell:A variable viscosity model |
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| 作者姓名： | 朱涛 冯锐 |
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| 作者单位： | Institute of Geophysics，China Earthquake Administration，Beijing100081，China，Lanzhou Institure of Seismology，China Earthquake Administration，Lanzhou730000，China，Institute of Geophysics，China Earthquake Administration，Beijing100081，China |
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| 基金项目： | National Natural Science Foundation of China (49834020). |
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| 摘 要： | Introduction The velocity field of surface plate motion can be split into a poloidal and a toroidal parts.At the Earth′s surface,the toroidal component is manifested by the existence of transform faults,and the poloidal component by the presence of convergence and divergence,i.e.spreading and subduc-tion zones.They have coupled each other and completely depicted the characteristics of plate tec-tonic motions.The mechanism of poloidal field has been studied fairly clearly which is related to …
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| 收稿时间： | 5 December 2003 |
| 修稿时间： | 27 August 2004 |
Nonlinear free thermal convection in a spherical shell: A variable viscosity model |
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| ZHU Tao,FENG Rui.Nonlinear free thermal convection in a spherical shell:A variable viscosity model[J].Acta Seismologica Sinica(English Edition),2005,18(2):206-217. |
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| Authors: | ZHU Tao FENG Rui |
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| Institution: | 1. Institute of Geophysics, China Earthquake Administration, Beijing 100081, China;Lanzhou Institure of Seismology, China Earthquake Administration, Lanzhou 730000, China
2. Institute of Geophysics, China Earthquake Administration, Beijing 100081, China |
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| Abstract: | In mantle convection models, the mantle viscosity is generally assumed constant or dependent on depth. In this paper, a laterally
variable viscosity is introduced into mantle convection model in which the mantle viscosity consists of a constant background
and latitude-dependent viscosity with small fluctuations. The features of toroidal field dependent on depth and Rayleigh number
are discussed under two boundary conditions, i.e., the top rigid and bottom stress-free boundaries (R-F boundary for short) and both rigid ones (R-R boundary for short), respectively.
The results show that the energy of toroidal field mainly concentrates in the middle and upper parts of a spherical shell,
and the ratio of toroidal to total velocities amounts to only a few percents and hardly depends on Rayleigh number, while
the convection patterns of toroidal field have been strongly affected by Rayleigh number. It is found that the convection
patterns and velocities of toroidal field have obvious differences in latitudinal direction, which clearly reflects the effects
of lateral mantle viscosity variations on the convection patterns. These preliminary results give us a possible hint to study
some global tectonic phenomena, e.g. the asymmetry of the southern and northern hemispheres and the Earth’s differential rotation.
Foundation item: National Natural Science Foundation of China (49834020).
Contribution No. 05FE3006, Institute of Geophysics, China Earthquake Administration. |
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| Keywords: | variable viscosity thermal free convection nonlinear the component of toroidal field |
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