On the model of equatorial Magnetic-Archimedes-Coriolis waves
propagating at Earth's core surface and the potential implications
Abstract
The purposes of this work are (1) clarifying the specific latitude range
in which the currently physical model of the equatorial trapped
Magnetic-Archimedes-Coriolis (namely eMAC) waves propagating atop the
Earth’s core can own the enough accuracy to describe the hydromagnetic
waves; (2) presenting the systematically analytical expressions to
represent the physical properties (e.g., the equatorial confinement and
latitudinal distribution, damping rate α, eigen-period T) of the eMAC
waves. Here, the new results indicate that: 1) the eMAC wave model can
own the high accuracy (i.e., the relative errors are less than 5%) to
describe the core waves in the regions with latitude below 25 degrees ;
2) the equatorial confinement and latitudinal distribution law is
essentially governed by a specific solution form with the typical
Hermite polynomial term of degree n; 3) the damping rate can be
estimated by α ≈-π^2/(μσH^2) (μ being the vacuum permeability, σ
being the core electrical conductivity; H being the stratified layer
thickness of the core), showing that the magnetic diffusivity η
(=1/(μσ))can cause the ohmic dissipation of the waves; besides, the H
value is predicted to be larger than 20km, when T matches the observed
8.5yr period. This work also presents the analytical models for the
perturbed magnetic fields due to the eMAC waves, presenting that the
azimuthal perturbed magnetic field bφ(with degree n=1) is mainly
confined to the equatorial regions with latitude below
~15 degrees, the profile of which coincides with the
observed core surface azimuthal flows.