Precessionally-driven dynamo in a fluid layer

More than a half century ago, Bullard conjectured that the motions necessary to generate the Earth's magnetic field in the Earth's electrically-conducting fluid core might be driven by the luni-solar precession. All that has been unequivocally established in the intervening 55 years is that precession can in principle supply the geodynamo with abundant power. The question of whether the geodynamo can draw on this power is still unanswered, though it seems probable from the work of Tilgner [Physics Fluids 17 (3): Art. No. 034104, 2005] that it can do so. Two types of precession-driven flows may be distinguished: in spherical precession, the mantle transmits motion to the core by viscous coupling; in non-spherical precession, the oblateness of the core-mantle boundary creates core motion through pressure differences. Non-spherical precession is geophysically the more relevant, and has been studied in simple, plane-layer geometry by Mason and Kerswell [Journal of Fluid Mechanics, 471: 71-106, 2002]. We report on further developments of their model, including also the effects of a self-generated magnetic field.