Investigating the Influence of the Magnetostrophic Magnetorotational Instability on the Dynamo Action in Planetary Interiors and their Exterior Field

原则上，即使存在少量的微分旋转，也可以在地球的外液核中产生一种简单的、改进的磁旋不稳定性（MRI） （Petitdemange, Dormy, Balbus， GRL,35, 2008）。我们将这种不稳定性称为磁转核磁共振成像（MS-MRI）。（“磁转”指的是随着不稳定性的发展，科里奥利力和洛伦兹力之间的主要平衡。）我们发现，当角动量向外传递时，MS-MRI主要通过减小初始剪切剖面的大小来饱和。因此，MS-MRI可能会约束行星剪切剖面。例如，在类木星行星上，磁场可能会破坏并最终调节这颗行星的导电带。我们建议使用恶搞代码（Dormy et al. 1998）将行星内部的非线性模拟扩展到三维空间。我们将通过从我们的计算中提取可观察的特征来将这些模拟置于观测的基础上。这些包括总的发电机特性（例如，在太阳系行星中是否存在发电机活动，地球的磁性历史，以及是小尺度还是大磁场占主导地位），以及等旋转表面的形状。因此，该建议是“行星磁学”优先计划“协同跨学科方法”的重要组成部分，将最近发现的物理效应与新开发的工具相结合，通过计算机模拟行星内部和发电机进行数据采集和分析。

A simple, modified version of the magnetorotational Instability (MRI) can, in principle, develop in the Earth’s outer liquid core if even a small amount of differential rotation is present (Petitdemange, Dormy, Balbus, GRL,35, 2008). We refer to this instability as the Magnetostrophic MRI (MS-MRI). (``Magnetostrophic’’ refers to a dominant balance between the Coriolis and Lorentz forces as the instability develops.) We have found that as angular momentum is transported outward, the MS-MRI saturates primarily by reducing the magnitude of the initial shear profile. It is therefore possible that the MS-MRI may constrain planetary shear profiles. For example, in Jupiter-like planets, the magnetic field may destabilize, and ultimately regulate, the conducting zone of this planet. We propose to extend our non-linear simulations of planetary interiors, using the PARODY code (Dormy et al. 1998), to three dimensions. We will place these simulations on an observational footing by extracting the observable features from our calculations. These include gross dynamo properties (e.g., whether dynamo activity is present in the solar system planets, the magnetic history of the earth, and whether small scale or large fields dominate), and the shapes of isorotational surfaces. Thus, this proposal is an essential part of the “synergistic interdisciplinary approach” of the Priority Program “Planetary Magnetism”, in combining a recently discovered physical effect with newly developed tools for data acquisition and analysis via computer simulations of planetary interiors and dynamos.