Parameterization of the Lorentz to Coriolis Force Ratio in Planetary Dynamos

Thursday, 17 December 2015
Poster Hall (Moscone South)
Krista M Soderlund, University of Texas, Institute for Geophysics, Austin, TX, United States, Andrey Alexandrovich Sheyko, ETH Swiss Federal Institute of Technology Zurich, Institut fur Geophysik, Zurich, Switzerland, Eric M King, U.S. Global Development Lab, Washington, DC, United States and Jonathan M Aurnou, University of California Los Angeles, Los Angeles, CA, United States
The Lorentz to Coriolis force ratio is an important parameter for the dynamics of planetary cores: it is expected that dynamos with dominant Coriolis forces will be driven by fundamentally different archetypes of fluid motions than those with co-dominant Lorentz forces. Using a suite of geodynamo simulations, we have tested several parameterizations of the Lorentz to Coriolis force ratio against direct calculations and developed a scaling estimate to predict this ratio for planetary cores. Our results suggest that the Earth's core is likely to be in magnetostrophic balance where the Lorentz and Coriolis forces are comparable. The Lorentz force may also be significant in Jupiter's core, where it is predicted to be approximately a factor of ten less than the Coriolis force. Magnetic fields become increasingly sub-dominant for the other planets: the Coriolis force is predicted to exceed the Lorentz force by at least two orders of magnitude within the cores of Saturn, Uranus/Neptune, Ganymede, and Mercury.