Rotating thermal convection in a full sphere with heterogeneous temperature boundary conditions
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2025-07
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Journal Article
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yes
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Abstract
The large-scale thermal inhomogeneity at the Earth's core mantle boundary generates lateral thermal winds, which can penetrate the core's interior due to the Coriolis force, and interact with the convecting flow. This boundary driving may provide an additional mechanism for convection in the liquid core, aside from the secular cooling, prior to the nucleation of the inner core. To understand the combined effects of boundary driving and secular cooling on the hydrodynamic process of the core without an inner boundary, we perform direct numerical simulations of a Boussinesq fluid in a rotating and internally heated full sphere. The boundary of the sphere is stress-free, with a fixed-temperature boundary condition imposed proportional to the $Y_{mm}$ spherical harmonic function ($m=1,2,3$), and an inhomogeneity parameter $\epsilon$ quantifying the relative magnitude of the boundary inhomogeneity. At Prandtl number of 1 and Ekman number of $3\times 10<^>{-4}$, the diagnostics, time-dependence and field morphology of the flow are investigated for a range of inhomogeneity parameters $0.02\le \epsilon \le 0.50$ and Rayleigh numbers $0.1\le \mathrm{ Ra}/\mathrm{ Ra}_\mathrm{ c}\le 1.9$, where $\mathrm{ Ra}_\mathrm{ c}$ is the critical Rayleigh number for convection in the homogeneous boundary case. Focusing on the $Y_{22}$ boundary conditions, we find the existence of four distinct flow regimes, that exhibit different flow morphologies. We further differentiate between them through the differences exhibited in the heat transport and dissipation rate as functions of $\mathrm{ Ra}$ and $\epsilon$. In particular, it is observed that the viscous and thermal dissipation of the flow varies as $\epsilon <^>2$, in the range investigated.
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242 (1)
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Oxford University Press
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Subject
Core; Non-linear differential equations; Numerical modelling; Core-mantle boundary
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03734 - Jackson, Andrew / Jackson, Andrew
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Funding
219247 - Dynamics of the Earth's core under the plesio-geostrophy paradigm (SNF)
227702 - 10000683 - Earth’s core dynamics: dynamo action and constraints on the inner core (SNF)
833848 - Unravelling Earth’s magnetic history and processes UEMHP (EC)
227702 - 10000683 - Earth’s core dynamics: dynamo action and constraints on the inner core (SNF)
833848 - Unravelling Earth’s magnetic history and processes UEMHP (EC)