Inertial waves identified in the Earth's fluid outer core

Abstract

Several inertial waves have been identified in the long period gravimetric data of Melchior and Ducarme¹. These hydrodynamical waves which only exist because of the Earth's rotation, must be in the Earth's fluid outer core. Close proximity of the observed periods to those predicted for a homogeneous fluid suggests the waves should be labelled inertial because buoyancy and compressibility effects must be small or self-cancelling. Some of the identified waves have azimuthal wavenumber one, consistent with their occurrence after large, deep earthquakes which probably excite the waves through a small perturbation in the Earth's rotation. Other waves are axially symmetric, consistent with a small change in the magnitude of the fluid core's rotation rate. All the waves decay more rapidly than would be expected for Ekman dissipation which suggests an additional dynamical damping associated with mantle-inner core coupling. The inertial waves identified here will serve as a precise tool for subsequent evaluation of models for core dynamics and the geodynamo.