Influence of possible inner-core motions on the polar motion and the gravity field

Provided that the figure axis of the inner core coincides with the dipole axis of the geomagnetic field, the relative rotation of the oblate inner core with respect to the outer core and the mantle can be determined. Because of the density difference between the inner and outer core, the assumed precessional motion of the inner core relative to the mantle is accompanied by a mass redistribution causing variations of polar motion. Assuming standard density models, it is found that variations of polar motion caused by variations of relative inner-core rotation due to that of the real dipole axis are similar to the decadal variations derived from observed pole coordinates. Calculations of the gravity potential show that the assumed relative rotation of the inner core causes gravity changes which may be detectable by modern satellite methods during the next decade. (C) 2000 Elsevier Science B.V. All rights reserved.