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

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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.