Precession in the rotation of the inner core seems to induce a precession of the geomagnetic field with a period of about 3.3X10 10 rad/s. This value corresponds to an elongation of 3.2X10 6 of the prolate spheroid of the inner core. Friction due to the liquid outer core seems compatible with a viscosity of the order of 10 4 Pa.s (10 5 poises).On the other hand, gravitational pulsations could be an adequate mechanism for producing magnetics reversals.
