论文标题
地球外部芯底部的浆液f层的政权图
A regime diagram for the slurry F-layer at the base of Earth's outer core
论文作者
论文摘要
在地球外核底部p波速度放缓的地震观察结果表明存在一个被称为F层的稳定区域。这提出了一个重要的问题：驱动Geodynamo的光元素如何通过稳定分层的层而不会干扰它？我们将F层视为含有固体颗粒的浆液，分散在液态铁合金中，将其下雪朝向内核。我们提供了一个制度图，显示了浆液f层的动力学在改变关键参数时如何变化：péclet编号（$ pe $），对流与化学扩散之间的比率； Stefan编号（$ ST $），明智和潜热之间的比率；和刘易斯号（$ le $），热量扩散率之间的比率。我们获得了四个与稳定，部分稳定，不稳定且无浆液相对应的制度。当层的底部的热流超过顶部的热流时，没有发现浆液，而当对流克服热扩散（$ pe \ gtrsim le $）时，就会出现稳定的分层浆液，而这些泥浆在与地球核心相关的广泛参数上存在。我们的结果估计，稳定的f层给出了最大的内部核心边界（ICB）体波密度跳跃的$Δρ_\ textrm {bod} \ leq 534 \ \ \ \ \ \ \ \ \ \ \ mathrm {kg} \ mathrm {m Mathrm {m}文献中报告了Δρ_\ textrm {bod} \ leq 1,100 \ \ mathrm {kg} \ mathrm {m}^{ - 3} $。凭借高热电导率，该模型可以预测内部核心年龄在$ 0.6 $和$ 1.2 \ \ \ \ Mathrm {ga} $之间，这与其他核心进化模型一致。我们的结果表明，具有较高核心电导率的浆液模型可以预测F层和核心的地球物理特性，该特性与独立的地震和地球动力学计算一致。
Seismic observations of a slowdown in P wave velocity at the base of Earth's outer core suggest the presence of a stably-stratified region known as the F-layer. This raises an important question: how can light elements that drive the geodynamo pass through the stably-stratified layer without disturbing it? We consider the F-layer as a slurry containing solid particles dispersed within the liquid iron alloy that snow under gravity towards the inner core. We present a regime diagram showing how the dynamics of the slurry F-layer change upon varying the key parameters: Péclet number ($Pe$), the ratio between advection and chemical diffusion; Stefan number ($St$), the ratio between sensible and latent heat; and Lewis number ($Le$), the ratio between thermal and chemical diffusivity. We obtain four regimes corresponding to stable, partially stable, unstable and no slurries. No slurry is found when the heat flow at the base of the layer exceeds the heat flow at the top, while a stably-stratified slurry arises when advection overcomes thermal diffusion ($Pe \gtrsim Le$) that exists over a wide range of parameters relevant to the Earth's core. Our results estimate that a stably-stratified F-layer gives a maximum inner-core boundary (ICB) body wave density jump of $Δρ_\textrm{bod} \leq 534 \ \mathrm{kg} \mathrm{m}^{-3}$ which is compatible with the lower end of the seismic observations where $280 \leq Δρ_\textrm{bod} \leq 1,100 \ \mathrm{kg} \mathrm{m}^{-3}$ is reported in the literature. With high thermal conductivity the model predicts an inner core age between $0.6$ and $1.2 \ \mathrm{Ga}$, which is consistent with other core evolution models. Our results suggest that a slurry model with high core conductivity predicts geophysical properties of the F-layer and core that are consistent with independent seismic and geodynamic calculations.
