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首页> 外文期刊>Earth and Planetary Science Letters: A Letter Journal Devoted to the Development in Time of the Earth and Planetary System >Conditions for Earth-like geodynamo models
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Conditions for Earth-like geodynamo models

机译：类地线模型的条件

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摘要

For many published dynamo models an Earth-like magnetic field has been claimed. However, it has also been noted that as the Ekman number (viscosity) is lowered to less unrealistic values, the magnetic field tends to become less Earth-like. Here we define quantitative criteria for the degree of semblance of a model field with the geomagnetic field, based on the field morphology at the core-mantle boundary. We consider the ratio of the power in the axial dipole component to that in the rest if the field, the ratios between equatorially symmetric and antisymmetric and between zonal and non-zonal non-dipole components, and a measure for the degree of spatial concentration of magnetic flux at the core surface. We also briefly discuss shortcomings of possible other criteria for an Earth-like model. We test the compliance with our criteria for a large number of dynamo models driven by imposed temperatures at their inner and outer boundaries that cover the accessible parameter space. We order models according to their magnetic Reynolds number Rm (ratio of advection to diffusion of magnetic field) and magnetic Ekman number E_η (ratio between rotation period and magnetic diffusion time). Requirements for an Earth-like field morphology are that E_η<10~(-4) and that Rm falls into a limited range that depends on E_η. Higher values of Rm are required at low values of E_η. Extrapolating the boundaries of compliant dynamos in this parameter space to the Earth's value of E_η suggests that Earth-like dynamos exist all the way between present model values and parameter values of the geodynamo. We also study a more limited set of dynamo models with flux boundary conditions. The nature of the boundary condition and the distribution of sources and sinks of buoyancy have a secondary influence on the field morphology.
机译：对于许多已发布的发电机模型，都要求有类似地球的磁场。然而，还已经注意到，随着埃克曼数（粘度）降低到不太现实的值，磁场倾向于变得不像地球。在此，我们根据岩心-地幔边界处的场形态，为模型场与地磁场的相似度定义了定量标准。如果考虑磁场，我们考虑轴向偶极子分量的功率与其余部分的功率之比，赤道对称和反对称之间以及区域和非区域非偶极子分量之间的比率，以及度量空间集中度的方法。磁芯表面的磁通量。我们还将简要讨论类似地球的模型可能存在的其他标准的缺点。我们测试了由内部和外部边界（覆盖可访问参数空间）施加的温度驱动的许多发电机模型是否符合我们的标准。我们根据模型的磁雷诺数Rm（对流与磁场扩散的比率）和磁埃克曼数E_η（旋转周期与磁扩散时间之间的比率）订购模型。类地场形态的要求是E_η<10〜（-4），Rm落在取决于E_η的有限范围内。在较低的E_η值下需要较高的Rm值。在此参数空间中将顺应性发电机的边界外推到地球的E_η值，表明类地球的发电机始终存在于当前模型值和测地发电机的参数值之间。我们还研究了带有通量边界条件的更有限的发电机模型集。边界条件的性质以及浮力源和汇的分布对场形态具有次要影响。

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