Abstract The dynamo effect is the most popular candidate to explain the non-primordial magnetic fields of astrophysical objects. Although many systematic studies of parameters have already been made to determine the different dynamical regimes explored by direct numerical geodynamo simulations, it is only recently that the regime corresponding to the outer core of the Earth characterized by a balance of forces between the Coriolis and Lorentz forces is accessible numerically. In most previous studies, the Lorentz force played a relatively minor role. For example, they have shown that a purely hydrodynamic parameter (the local Rossby number Rol) determines the stability domain of dynamos dominated by the axial dipole (dipolar dynamos). In this study, we show that this result cannot hold when the Lorentz force becomes dominant. We model turbulent geodynamo simulations with a strong Lorentz force by varying the important parameters over several orders of magnitude. This method enables us to question previous results and to argue on the applications of numerical dynamos in order to better understand the geodynamo problem. Strong dipolar fields considerably affect the kinetic energy distribution of convective motions which enables the maintenance of this field configuration. The relative importance of each force depends on the spatial length scale, whereas Rol is a global output parameter which ignores the spatial dependency. We show that inertia does not induce a dipole collapse as long as the Lorentz and the Coriolis forces remain dominant at large length scales.

中文翻译：

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地球动力学模拟中磁场对场形态和反转的影响

摘要 发电机效应是解释天体非原初磁场最流行的候选方法。尽管已经对参数进行了许多系统的研究，以确定通过直接数值地球发电机模拟探索的不同动力学状态，但直到最近，对应于地球外核的状态才以科里奥利力和洛伦兹力之间的力平衡为特征可通过数字访问。在以前的大多数研究中，洛伦兹力的作用相对较小。例如，他们已经表明，纯流体动力学参数（局部罗斯比数 Rol）决定了由轴向偶极子（偶极发电机）主导的发电机的稳定域。在这项研究中，我们表明当洛伦兹力占主导地位时，这个结果不能成立。我们通过在几个数量级上改变重要参数来模拟具有强洛伦兹力的湍流地球发电机模拟。这种方法使我们能够质疑以前的结果并就数值发电机的应用进行争论，以便更好地理解地球发电机问题。强偶极场会显着影响对流运动的动能分布，这使得维持这种场配置成为可能。每个力的相对重要性取决于空间长度尺度，而 Rol 是忽略空间依赖性的全局输出参数。我们表明，只要洛伦兹力和科里奥利力在大长度尺度上仍然占主导地位，惯性就不会引起偶极子坍缩。