Geodynamo and planetary dynamos
Investigating the dynamo of the Ice Giants
The interior structures and dynamics of Uranus and Neptune remain largely mysterious owing to the lack of data regarding their respective magnetic fields. Nevertheless, current observations of their predominantly multipolar magnetic fields, retrograde equatorial zonal flows, and very low luminosity make them stand out against the better-studied Gas Giants. It is thus important to understand the dynamo regimes that result in such observations - this work investigates the dynamo regions of the Ice Giants based on most recent ab initio interior structure models, conducting a sweep across three main dimensionless control parameters (Ekman, Rayleigh, and magnetic Prandtl numbers) to determine the regimes under which ice giant-like features are obtained. Moreover, this work serves as a basis for future investigations, in which more complex structures related to chemical compositions may be studied.
People involved: Sofya Dobrynina, Stefano Maffei
The precession-driven geodynamo
Precession is one aspect of the variability of Earth's rotation. It has been theorised that it could drive the geodynamo, but past investigations have been hampered by the difficulty of solving the governing equations in the aspherical geometries that are (most likely) the problem's key ingredient.
In this work we show how the governing equations within a variably rotating spheroid may be transformed onto a spherical computational domain. Additional coupling between spherical harmonic degrees is the computational cost of such a transformation, but this coupling is shown to be qualitatively similar to the coupling that is already dealt with routinely within implicit implementations of the Coriolis force. On the other hand, the computational gain of this approach is to permit the use of powerful spectral representations of fields on the unit ball, representations that are not readily available in spheroidal geometries. This approach should allow investigation of the precession-driven dynamo at lower Ekman number than previously possible.
People involved: Matthew Maitra, Andrew Jackson, Jerome Noir