THE MAGNETOSTROPHIC RISE OF A BUOYANT PARCEL IN THE EARTHS CORE

The dynamics of a buoyant parcel (or blob) of fluid released from the mushy zone on the inner core boundary (ICB) is considered. Estimates o f the density defect and of the rise velocity are obtained from consid eration of mass conservation and magnetostrophic force balance. When L orentz and Coriolis forces are of comparable orders of magnitude, the disturbance remains localized in a neighbourhood of the blob even in t he absence of viscous effects, and an inviscid analysis is possible. T he instantaneous velocity and magnetic field associated with a given l ocalized buoyancy distribution are then determined, and on the assumpt ion that the velocity is approximately uniform throughout the blob, it s trajectory from ICB to core-mantle boundary (CMB) is deduced. Both w estward drift and poleward migration of erupting field loops are indic ated. The effects of turbulent diffusion on the blob are considered. T he prospects for constructing a dynamo theory based on this 'blob scen ario' are discussed.