On the unsteady hydromagnetic perturbations at the earth's core-mantle interface

Abstract

The unsteady hydromagnetic perturbations which may be induced at the core-mantle interface within the Earth are investigated by analyzing the perturbations generated within an incompressible viscous electrically conducting fluid near an impulsively accelerated, rotating infinite flat boundary of variable electrical conductivity. The form of the conductivity distribution is chosen to simplify the analysis as well as to mimic the decrease in conductivity of the mantle with the distance from the core-mantle boundary. Attention is focused upon the strength of the coupling between the fluid and the boundary as a function of time. It is found that the spin-up time for a contained fluid is lengthened by the response time of the mantle to a magnetic perturbation. Also, it is found that, for ranges of parameters modelling conditions within the Earth, Alfvén waves are only weakly excited by an impulsive change in rotation rate of the mantle.