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arXiv 0709.3333physics.geo-ph
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地球外核的粘度

Viscosity of Earth's Outer Core

D. E. Smylie, Andrew Palmer

摘要:

整个流体外核的粘度分布是通过使用支配压力和温度依赖性的阿克里尼乌斯定律的微分形式在测量的边界值之间进行插值而得到的。逆行和逆行自由核章动都处于自由衰变中的发现(Palmer和Smylie,2005)允许在外核顶部直接测量粘度,而内核两个赤道平移模式的旋转分裂的减少允许在底部测量粘度。我们在顶部发现2,371 ± 1,530 Pa.s,在底部发现1.247 ± 0.035 x 10^11 Pa.s。Brazhkin(1998)和Brazhkin和Lyapin(2000)通过实验室实验的阿克里乌斯外推法得出顶部为10^2 Pa. s,底部为10^11 Pa.s,我们采用阿克里乌斯定律的微分形式沿熔化温度曲线进行内推,以找到整个外核的粘度分布。我们发现,测量的边界值之间的变化是密切的对数线性。由实验室实验的Arabius外推法发现的粘性边界值与从自由堆芯章动和内核平移模式中发现的粘性边界值非常一致,这表明堆芯流是层流,返回的粘性是其分子值的量度。在发电机理论家有时假设的强湍流对流存在的情况下,情况就不是这样了。局部埃克曼数的范围从外核底部的10^-2到顶部的10^-10。除了在外核的非常低的部分,埃克曼数在10^-4到10^-5的范围内,或者更低,在这些部分中出现数值发电机和实验室旋转流体实验的层流。

英文摘要:

A viscosity profile across the entire fluid outer core is found by interpolating between measured boundary values, using a differential form of the Arrhenius law governing pressure and temperature dependence. The discovery that both the retrograde and prograde free core nutations are in free decay (Palmer and Smylie, 2005) allows direct measures of viscosity at the top of the outer core, while the reduction in the rotational splitting of the two equatorial translational modes of the inner core allows it to be measured at the bottom. We find 2,371 plus/minus 1,530 Pa.s at the top and 1.247 plus/minus 0.035 x 10^11 Pa.s at the bottom. Following Brazhkin (1998) and Brazhkin and Lyapin (2000) who get 10^2 Pa.s at the top, 10^11 Pa.s at the bottom, by an Arrhenius extrapolation of laboratory experiments, we use a differential form of the Arrhenius law to interpolate along the melting temperature curve to find a viscosity profile across the outer core. We find the variation to be closely log-linear between the measured boundary values. The close agreement of the boundary values of viscosity, found by Arrhenius extrapolation of laboratory experiments, with those found from the free core nutations, and the inner core translational modes, suggests that core flows are laminar and that the returned viscosities are measures of their molecular values. This would not be the case in the presence of the vigorous turbulent convection sometimes postulated by dynamo theorists. The local Ekman number is found to range from 10^-2 at the bottom of the outer core to 10^-10 at the top. Except in the very lower part of the outer core, Ekman numbers are in the range 10^-4 to 10^-5, or below, in which the laminar flows of numerical dynamos and laboratory rotating fluids experiments occur.

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