Open AccessInternal waves in the earth's core
Author(s) -
Olsen Peter
Publication year - 1977
Publication title -
geophysical journal of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.302
H-Index - 168
eISSN - 1365-246X
pISSN - 0016-8009
DOI - 10.1111/j.1365-246x.1977.tb04196.x
Subject(s) - outer core , internal wave , stratification (seeds) , inviscid flow , inner core , physics , inertial wave , buoyancy , stratified flows , mechanics , classical mechanics , earth's rotation , amplitude , mantle (geology) , geophysical fluid dynamics , gravity wave , perturbation (astronomy) , geophysics , stratified flow , wave propagation , mechanical wave , longitudinal wave , turbulence , seed dormancy , germination , botany , quantum mechanics , dormancy , biology
This paper investigates possible long‐period oscillations of the earth's fluid outer core. Equations describing free oscillations in a stratified, self‐gravitating, rotating fluid sphere are developed using a regular perturbation on the equations of hydrodynamics. The resulting system is reduced to a finite set of ordinary differential equations by ignoring the local horizontal component of the earth's angular velocity vector, Ω, and retaining only the vertical component. The angular dependence of the eigensolutions is described by Hough functions, which are solutions to Laplace's tidal equation. The model considered here consists of a uniform solid elastic mantle and inner core surrounding a stratified, rotating, inviscid fluid outer core. The quantity which describes the core's stratification is the Brunt—Väisälä frequency N , and for particular distributions of this parameter, analytical solutions are presented. The interaction of buoyancy, and rotation results in two types of wave motion, the amplitudes of which are confined predominantly to the outer core: (1) internal gravity waves which exist when N 2 > 0, and (2) inertial oscillations which exist when N 2 <4Ω 2 . For a model with a stable density stratification similar to that proposed by Higgins & Kennedy (1971), the resulting internal gravity wave eigenperiods are all at least 8 hr, and the fundamental modes have periods of at least 13 hr. A model with an unstable density stratification admits no internal gravity waves but does admit inertial oscillations whose eigenperiods have a lower bound of 12hr.