Abstract
A high-degree (degree l=6 and order m=0, 1, 2, ..., l. High-order model for short) and steady thermal free convective motion of an infinite Prandtl number and Boussinesq fluid in a spherical shell is calculated by a Galerkin method. Convection is driven by an imposed temperature drop across top rigid and bottom stress-free isothermal boundaries only heated from below of the shell. In this paper, the scalar poloidal and fluctuating temperature fields are expanded into associated Legendre polynomials with degree l=6 and order m=0, 1, 2, …, l. Compared with zero-order model (degree l=6 and order m=0), from which 2-D longitudinal (r-θ) profiles can be obtained, high-order model can provide a series of southerly (r-θ), easterly (r-ϕ) and radial (θ-ϕ) velocity profiles, which probably reveal more detail features of mass motion in the mantle. It is found that Rayleigh number has great effects on the patterns and velocities of thermal free convection and controls the relative ratio of hot and cold plume in the shell. Probably, the present results mainly reveal the mass motion in the lower mantle, while the striking differences of convection patterns from velocities at different positions have important geodynamical significances.
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Foundation item: National Natural Science Foundation of China (49834020).
Contribution No. 05FE3005, Institute of Geophysics, China Earthquake Administration.
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Zhu, T., Feng, R. The patterns of high-degree thermal free convection and its features in a spherical shell. Acta Seimol. Sin. 18, 12–26 (2005). https://doi.org/10.1007/s11589-005-0002-3
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DOI: https://doi.org/10.1007/s11589-005-0002-3