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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 >Axial vs. equatorial dipolar dynamo models with implications for planetary magnetic fields
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Axial vs. equatorial dipolar dynamo models with implications for planetary magnetic fields

机译：轴向与赤道偶极发电机模型对行星磁场的影响

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We present several numerical simulations of a self-consistent dynamo model in a rotating spherical shell. The solutions have two different field configurations. Besides magnetic fields dominated by the axial dipole component, we also find configurations where a dipole in the equatorial plane is the dominating component. Both types are stable in a parameter regime of intermediate shell thickness and Rayleigh numbers close to onset of convection. Axial dipole solutions are subcritical in all the simulations explored while the equatorial dipole cases are supercritical at low Rayleigh numbers but become metastable at higher Rayleigh numbers. The magnetic field strength saturates at a much lower amplitude for the equatorial dipole dynamos, and the Elsasser number is significantly smaller than in the axial configuration. The reason is that the mainly horizontal field in the equatorial dipole solution is incompatible with the motion of convective cyclones and anticyclones. The axial dipole field, on the other hand, is predominantly aligned with the axis of anticyclones, only cyclones are disrupted by horizontal field lines passing through. This configuration can therefore accomodate stronger convective flows and, consequently, is the only one remaining stable at higher Rayleigh numbers. These arguments should pertain in all planetary dynamos that are governed by strong rotational constraints. They offer an explanation why the Elsasser numbers inferred for Uranus and Neptune are much lower than the Elsasser numbers of Jupiter, Saturn, and Earth.
机译：我们目前在旋转球壳中的自洽发电机模型的几个数值模拟。解决方案具有两种不同的现场配置。除了由轴向偶极子分量控制的磁场外，我们还发现在赤道平面中偶极子为主要分量的配置。两种类型在中间壳厚度和瑞利数接近对流开始的参数范围内都是稳定的。在所有探索的模拟中，轴向偶极子解决方案都是次临界的，而赤道偶极子情况在低瑞利数下是超临界的，而在较高瑞利数下变为亚稳态的。对于赤道偶极发电机，磁场强度以低得多的幅度饱和，并且Elsasser数明显小于轴向构造。原因是赤道偶极子解中的主要水平场与对流旋风和反旋风的运动不兼容。另一方面，轴向偶极子场主要与反旋风器的轴对齐，只有旋风器被穿过的水平场线打断。因此，该配置可以适应更强的对流，因此，是在较高瑞利数下唯一保持稳定的配置。这些论点应适用于所有受强旋转约束控制的行星动力。他们提供了一个解释，为什么为天王星和海王星推断出的Elsasser数要比木星，土星和地球的Elsasser数低得多。

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